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All Textbook Solutions for Chemistry for Engineering Students

8.56PAE 8.57PAE 8.58PAE 8.59PAE 8.60PAE 8.61 Distinguish between a block copolymer and a graft copolymer.8.62PAE 8.63PAE 8.64PAE 8.65PAE 8.66 What structural characteristics are needed for additives such as plasticizers?8.67PAE 8.68PAE 8.69PAE 8.70PAE 8.71PAE 8.72PAE 8.73PAE 8.74PAE 8.75 Using pentagons, draw arrangements that demonstrate low packing efficiency and higher packing efficiency.8.76 Using circles, draw regular two-dimensional arrangements that demonstrate low packing efficiency and high packing efficieny.8.77 What is the difference between a bonding orbital and an antibonding orbital?8.78PAE 8.79 Most gaseous compounds consist of small molecules, while polymers are never gaseous at room temperature. Explain this observation based on intermolecular forces.8.80 Why are dipole—dipole forces typically stronger than dispersion forces?8.81 Carbon tetrachloride (CCl4) is a liquid at room temperature and pressure, whereas ammonia (NH3) is a gas. How can these observations be rationalized in terms of intermolecular forces?8.82PAE 8.83PAE 8.84PAE 8.85PAE 8.86PAE 8.87 Use the vapor pressure curves illustrated here to answer the questions that follow. (a) What is the vapor pressure of ethanol (C2H5OH) at 60°C? (b) Considering only carbon disulfide (CS2) and ethanol, which has the stranger intermolecular forces in the liquid state? (c) At what temperature does heptane (C7H16) have a vapor pressure of 500 mm Hg? (d) What are the approximate normal boiling pains of each of the three substances? (e) At a pressure of 400 mm Hg and a temperature of 70°C, is each substance a liquid, a gas, or a mixture of liquid and gas?8.88PAE 8.89 The following data show the vapor pressure of liquid propane as a function of temperature (a) Plot a vapor pressure curve for propane and use it to estimate the normal boiling point. (b) Use your curve to estimate the pressure (in atm) in the propane rank supplying fuel for a gas barbecue grill on a hot summer day when the temperature is 95°F (c) What implications might your answer to part (b) have for an engineer designing propane storage tanks? T (°C) -100 -80 -60 -40 -20 0 20 P (torr) 22.4 100.6 328.8 856.9 1888.6 3665.6 6445.9 8.90PAE 8.91PAE 8.92PAE 8.93PAE 8.94PAE 8.95PAE 8.96 A business manager wants to provide a wider range of p- and n-type semiconductors as a strategy to enhance sales. You are the lead materials engineer assigned to communicate with this manager. How would you explain why there are more ways to build a p-type semiconductor from silicon than there are ways to build an n-type semiconductor from silicon?8.97 The doping of semiconductors can be done with enough precision to tune the size of the band gap in the material. Generally, in order to have a larger band gap, the dopant should be smaller than the main material. If you are a materials engineer and need a semiconductor that has lower conductivity thin pure silicon, what clement or elements could you use as your dopant? (You do not want either an n- or a p- type material) Explain your reasoning.8.98 If you know the density of material and the length of the edge of its cubic Iattice, how would you determine if it is face-centered cubic, body-centered cubic, or simple cubic Would you have to look up any information?8.99PAE 8.100PAE 8.101PAE 8.102PAE 8.103 Cryolite (Na3AlF6) is used in refining aluminum. Use the web to look up what this addition does for the process, and relate it to the concepts of intermolecular forces from this chapter.8.104PAE 8.105PAE Explain the economic importance of conversions between different forms of energy and the inevitability of losses in this process.• define work and beat using the standard sign conventions.• define state functions and explain their importance.• state the first law of thermodynamics in words and as an equation.• use calorimetric data to obtain values for E and H for chemical reactions.• define Hfo and write formation reactions for compounds.• explain Hess’s law in your own words.• calculate H for chemical reactions from tabulated heats of formation.9.1PAE 9.2PAE 9.3PAE 9.4PAE 9.5PAE 9.6PAE Define the term internal energy.How fast (in meters per second) must an iron ball with a mass of 56.6 g be traveling in order to have a kinetic energy of 15.75 J?What is the kinetic energy of a single molecule of oxygen if it is traveling at 1.5103m/s ?9.10 The kinetic energy of molecules is often used to induce chemical reactions. The bond energy in an O1 molecule is 8.221019J . Can an O2 molecule traveling at 780 m/s provide enough energy to break the O = O bond? What is the minimum velocity of an O2 molecule that would give a kinetic energy capable of breaking the bond if it is converted with 100% efficiency?9.11 Analyze the units of the quantity (pressurevolume) and show that they are energy units, consistent with the idea of PV-work.9.12 How many kilojoules are equal to 3.27 L atm of work?9.13PAE 9.14PAE 9.15 Carry out the following conversions of energy units: (a) 14.3 Btu Into calories, (b) 1.4105 cal into joules, (c) 31.6 mJ into Btu 9.16 According to Figure 9.2, the total energy supply in the United States in 2016 was 111.261015 Btu. Express this value in joules and in calories. FIGURE 9.2 Energy production and consumption (in quadrillion Btu) in the United States during the year 2016. The discussion in the text explains how to read this complex figure, which contains an enormous amount of information about the energy economy. Data come from the Department of Energy and do not always add up exactly as expected due to rounding and other issues.9.17 If a machine does 4.8103kJ of work after an input of 7.31104kJ of heat, what is the change in internal energy for the machine?9.18 Calculate (a) q when a system does 54J of work and its energy decreases by 72 J and (b) E for a gas that releases 38 J of heat and has 102 J of work done on it.9.19 If the algebraic sign of E is negative, in which direction has energy flowed?9.20 State the first law of thermodynamics briefly in your own words.9.21 Which type of energy heat or work, is valued more by society? What evidence supports your judgment?9.12 PV-work occurs when volume changes and pressure remains constant. If volume is held constant, can PV-work be done? What happens to Equation 9.2 when volume is held constant? E=q+w (9.2)9.23 Which system does not work: (a) E=436J , q=400J ; or E=317J , q=347J ?9.29 In which case is heat added to the system: (a) E=43J , w=40J ; or (b) E=31J , w=34J ?9.25PAE 9.26 Gas furnaces have achieved impressive efficiency levels largely through the addition of a second heat exchanger that condenses water vapor that would otherwise escape out the exhaust system attached to the furnace. How does this process improve efficiency?9.27PAE 9.28 When an electrical appliance whose power usage is X watts is run for Y seconds, it uses joules of energy. The energy unit used by electrical utilities in their monthly bills is the kilowatt-hour (kWh, that is, 1 kilowatt used for 1 hour). How many joules are there in a kilowatt-hour? If electricity costs $0.09 per kilowatt-hour, how much does it cost per mega joule?9.29PAE 9.30 For the example of shallow water and sandy beaches, which material has a larger heat capacity or specific heat? How does a hot day at the beach provide evidence for your answer?9.31 A metal radiator is made from 26.0 kg of iron. The specific heat of iron is 0.449Jg1C1 . How much heat must be supplied to the radiator to raise its temperature from 25.0 to 5 5.0°C?9.32 The material typically used to heat metal radiators is water. If a boiler generates water at 79.5°C, what mass of water was needed to provide the heat required in the previous problem? Water has a specific heat of 4.184Jg1 C1 .9.33 Copper wires used to transport electrical current heat up because of the resistance of the wire. If a 140-g wire gains 280 J of heat, what is the change in temperature in the wire? Copper has a specific heat of 0.384Jg1C1 .9.34 A copper nail and an iron nail of the same mass and initially at the same room temperature are both put into a vessel containing boiling water. Which one would you expect to reach 100°C first? Why?9.35 A piece of titanium metal with a mass of 20.8 g is heated in boiling water to 99.5°C and then dropped into a coffee cup calorimeter containing 75.0 g of water at 2 1.7°C. When thermal equilibrium is reached, the final temperature is 24.3°C. Calculate the specific heat capacity of titanium.9.36 Define the term calibration.9.37 A calorimeter contained 75.0 g of water at 16.95°C. A 93.3-g sample of iron at 65.58°C was placed in it, giving a final temperature of 19.68°C for the system. Calculate the heat capacity of the calorimeter. Specific heats are 4.184Jg1C1 for H2O and 0.444Jg1C1 for Fe.9.38 The energy densities of various types of coal are listed below: Anthracite 35 kJ/g Subbituminous 31 kJ/g Bituminous 28 kJ/g Lignite 26 kJ/g An unknown sample of one of these coals is burned in an apparatus with a calorimeter constant of 1.3 kJ/°C. When a 0.367-g sample is used, the temperature change is 8.75°C. Which type of coal is the sample?9.39 How much thermal energy is required to heat all of the water in a swimming pool by 1°C if the dimensions are 4 ft deep by 20 ft wide by 75 ft long? Report your result in megajoules.9.40PAE 9.41 Under what conditions does the enthalpy change equal the heat of a process?9.42 Why is enthalpy generally more useful than internal energy in the thermodynamics of real world systems?9.43PAE 9.44PAE 9.45 What happens to the temperature of a material as it undergoes an endothermic phase change? If heat is added, how can the temperature behave in this manner?9.46 The heat of fusion of pure silicon is 43.4 kJ/mol. How much energy would be needed to melt a 5.24-g sample of silicon at its melting point of 1693 K?9.47 If 14.8 kJ of heat is given off when 1.6 g of HCl condenses from vapor to liquid, what is Hcond for this substance?9.48 Calculate the energy required to convert 1.70 g of ice originally at 12.0 C into steam at 105 C.9.49 Hvap=31.3 kJ/mol for acetone. If 1.40 kg of water were vaporized to steam in a boiler, how much acetone (in kg) would need to be vaporized to use the same amount of heat?9.50 When a 13.0-g sample of NaOH(s) dissolves in 400.0 mL of water in a coffee cup calorimeter, the temperature of the water changes from 22.6°C to 30.7C Assuming that the specific heat capacity of the solution is the same as for water, calculate (a) the heat transfer from system to surroundings and (b) H for the reaction NaOH(s)Na+(aq)+OH(aq)9.51PAE 9.52 Write the formation reaction for each of the following substances. (a) CH4(g) , (b) C3H(l) , (c) HCI(g), (d) C6H12O6(s) , (e) NaF(s)9.53 Using these reactions, find the standard enthalpy change for the formation of 1 mol of PhO(s) from lead metal and oxygen gas. PbO(s)+C(graphite)Pb(s)+CO(g) H = 106.8 kJ 2C(graphite)+O2(g)2CO(g) H= -221.0 kJ If 250 g of lead reacts with oxygen to form lead(II) oxide, what quantity of thermal energy (in kJ) is ahsorhed or evolved?9.54 The phase change between graphite and diamond is difficult to observe directly. Both substances can be hurned, however. From these equations, calculate H for the conversion of diamond into graphite. C(s,graphite)+O2(g)CO2(g) H= -393.51 kJ C(s,diamond)+O2(g)CO2(g) H= -395.94 kJ 9.55 Hydrogen gas will react with either acetylene or ethylene gas. The thermochemical equations for these reactions are provided below. Write the thermochemical equation for the conversion of acetylene into ethylene by hydrogen gas. C2H2(g)+2H2(g)C2H6 H= -311 kJ C2H4(g)+H2(g)C2H6 H = -136 kJ 9.56 Using heats of formation tabulated in Appendix E, calculate the heats of reaction for the following. (a) C2H2(g)+52O2(g)2CO2(g)+H2O(l) (b) PCl3(g)+Cl2(g)PCl5(g) (c) C2H4(g)+H2O(g)C2H5OH(g) (d) Fe2O3(s)+2Al(s)Al2O3(s)+2Fe(l)9.57 The heat of combustion of butane is —2877 kJ/mol. Use this value to find the heat of formation of butane. (You may also need to use additional thermochemical data found in Appendix E.)9.58 For the reaction C2H2(g)+2H2(g)C2H6,H=136 kJ. What are the ratios that can be defined between moles of substances and energy?9.59 For the reaction N2(g)+O2(g)2NO(g),H=180.5kJ . How much energy is needed to generate 35 moles of NO(g)?9.60 Nitroglycenne, C3H5(NO3)3( l ), is an explosive most often used in mine or quarry blasting. It is a powerful explosive because four gases (N2, O2, CO2), and steam) are formed when nitroglycerine is detonated. In addition, 6.26 kJ of heat is given off per gram of nitroglycerine detonated, (a) Write a balanced thermochemical equation for the reaction, (b) What is H when 4.65 mol of products is formed?9.61 Silane, SiH4, burns according to the reaction, SiH4+2O2SiO2+2H2O , with H=1429 kJ. How much energy is released if 15.7 g of silane is burned?9.62 Sulfur trioxide can be removed from the exhaust gases of power plants hy reaction with lime. The relevant reaction is CaO(s)+SO4(g)CaSO4(s) , with H= -886 kJ. If 240 kg of SO3 is to be removed, how much heat is released?9.63 Reactions of hydrocarhons are often studied in the petroleum industry. One example is 2C3H8(g)C6H6(l)+5H2(g) , with H = 698 kJ. If 35 L of propane at 25C and 0.97 atm is to be reacted, how much heat must he supplied?9.64PAE 9.65 When 0.0157 g of a compound with a heat of combustion of —37.6 kJ/mol is burned in a calorimeter, 18.5 j of heat is released. What is the molar mass of the compound?9.66PAE 9.67PAE 9.68 What are some features of petroleum that make it such an attractive fuel?9.69 How are the roles of transmission substations and distribution substations in the electrical grid similar? How are they different?9.70 Residential electric service in the United States generally operates at 120 V, but transmission substations feed power onto the grid at 110 kV or higher. What advantage is realized by transmitting electricity at such a high voltage?9.71 In recent years, the notion of a “smart grid” has emerged. Do a web search and research the smart grid concept. How would the smart grid differ from the traditional grid?9.72 Although it can be a nuisance when a laptop computer freezes up and needs to be rebooted, we accept that as somewhat inevitable. But clearly the need to occasionally reboot the control system for the power grid would not be acceptable. Use the web to research ways that engineers ensure the reliability of crucial systems like the control infrastructure of the grid, and write a paragraph summarizing the main strategies employed.9.73 Without looking up any numerical data or doing calculations, predict whether the enthalpy change for each of the following reactions should he positive, negative, or zero. (a) H2O(l)H2O(s) (b) N2(g)2N(g) (c) CH4(g)+2O2(g)CO2(g)+2H2O(l) (d) CO2(s)CO2(g)9.74 Without looking up any numerical data or doing calculations, predict whether the following enthalpy changes should he positive, negative, or zero. (a) Hf for H2(g) (b) Hf for O(g) (c) Hfusion for H2O (d) Hcombusion for C3H8(g)9.75 Explain why each of the following chemical equations is not a correct formation reaction. (a) 4Al(s)+3O2(g)2Al2O3(s) (b) N2(g)+32H2(g)NH3(g) (c) 2Na(s)+O(g)Na2O(s)9.76 Which of the following are state functions? (a) the volume of a balloon, (b) the time it takes to drive from your home to your college or university, (c) the temperature of the water in a coffee cup, (d) the potential energy of a ball held in your hand 9.77 When a reaction is exothermic, is the sum of bond energies of products or of reactants greater?9.78PAE 9.79PAE 9.80PAE 9.81 A substance has the following properties: Hfusion = 10.0 kJ/mol Hvaporiztion = 20.0 kJ/mol Cp(solid) = 30 J/mol/K Cp(liquid) = 60 J/mol/K Cp(gas) = 30 J/mol/K Which of the four graphs below would he most consistent with these data? Explain how you are able to identify the correct graph.9.82 The specific heat of gold is 0.13 J g-1 K-1 and that of copper is 0.39 J g-1 K-1. Suppose that we heat both a 25-g sample of gold and a 25-g sample of copper to 80C and then drop them into identical beakers containing 100 mL of cold water at 10°C. When each beaker reaches thermal equilibrium, which of the following will be true, and why? (You should not need to calculate the actual temperatures here.) (a) Both beakers will be at the same temperature. (b) The beaker with the copper sample in it will be at a higher temperature. (c) The beaker with the gold sample in it will be at a higher temperature 9.83 A student performing a calorimetry experiment combined 100.0 mL of 0.50 M HCl and 100.0 mL of 0.50 M NaOH in a coffee cup calorimeter. Both solutions were initially at 20.0°C, but when the two were mixed, the temperature rose to 23.2°C. (a) Suppose the experiment is repeated in the same calorimeter but this time using 200 mL of 0.50 M HCl and 200.0 mL of 0.50 M NaOH. Will the T observed he greater than, less than, or equal to that in the first experiment, and why? (b) Suppose that the experiment is repeated once again in the same calorimeter, this time using 100 mL of 1.00 M HCl and 100.0 mL of 1.00 M NaOH. Will the T observed he greater than, less than, or equal to that in the first experiment, and why?9.84 Some claim it would be more logical to use heats of atomization, the energy required to convert any molecule to its separated atoms, rather than heats of formation for doing calculations with Hess's law. If you had a table of heats of atomization and calculated the combustion energy of a fuel, would you get the same answer as you would get using heats of formation? Explain your answer.9.85 The figure below shows a "self-cooling" beverage can. The can is equipped with an outer jacket containing sodium carbonate (Na2CO3), which dissolves in water rapidly and endothermically: Na2CO3(s)2Na+(aq)+CO32(aq) H= 67.7 kJ The user adds water to the outer jacket, and the heat absorbed in the chemical reaction chills the drink. The can contains 200 g of drink, the jacket contains 55 g of Na2CO3, and 100 g of water is to be added. If the initial temperatures of the can and the water are both 32°C on a summer day, what is the coldest temperature that the drink can reach? The can itself has a heat capacity of 40 J/C Assume that the Na2CO3 solution and the drink both have the same heat capacity as pure water, 4.184 J g-l C-l, (HINT: Treat this like a calorimetry problem.)9.86 You make some iced tea by dropping 134 g of ice into 500.0 mL of warm tea in an insulated pitcher. If the tea is initially at 20.0°C and the ice cubes are initially at 0.0°C, how many grams of ice will still be present when the contents of the pitcher reach a final temperature? The tea is mostly water, so assume that it has the same density (1.0 g/mL), molar mass, heat capacity (75.3 J K-1 mol-1), and heat of fusion (6.0 kJ/mol) as pure water. The heat capacity of ice is 37.7 J K-l mol-l.9.87 What will be the final temperature of a mixture made from equal masses of the following: water at 25.0 C, ethanol at 35.5 C, and iron at 95.0 C?9.88PAE 9.89 A sample of gas is 80.0% CH4 and 20.0% C2H6 by mass. What is the heat from the combustion of 1.00 g of this mixture? Assume the products are CO2 (g) and H2O (l).9.90 Many engineering designs must incorporate ways to dissipate energy in the form of heat. Water evaporators are common for this task. (a) What property of water makes it a good material for evaporators? {b} If an application could not use water, hut instead was forced to use a material with a value for the property in part (a) that was one half that of water, what changes would need to be made in the design?9.91 You want to heat the air in your house with natural gas (CH4). Assume your house has 275 m2(ahout 2800 ft2) of floor area and that the ceilings are 2.50 m from the floors. The air in the house has a molar heat capacity of 29.1 J mol-l K-l. (The number of moles of air in the house may he found by assuming that the average molar mass of air is 28.9 g/mol and that the density of air at these temperatures is 1.22 g/L.) What mass of methane do you have to burn to heat the air from 15.0 to 22.0°C?9.92PAE 9.93PAE 9.94PAE 9.95 How much heat is required to convert 250 g of water from liquid at 23°C: into steam at 107°C? (The necessary heat capacities and enthalpy changes can be found in the chapter or online.)9.96 Most first aid "cold packs" are based on the endothermic dissolution of ammonium nitrate in water: NH4NO3(s)NH4+(aq)+NO3(aq) H= 25.69 kJ A particular cold pack contains 50.0 g of NH4NO3 and 125.0 g of water. When the pack is squeezed, the NH4NO3dissolves in the water. If the pack and its contents are initially at 24.0°C, what is the lowest temperature that this bag could reach? (Assume that the ammonium nitrate solution has a specific heat of 4.25J g-l K-l, and that the heat capacity of the bag itself is small enough to be neglected.)9.97 Suppose that the working fluid inside an industrial refrigerator absorbs 680 J of energy for every gram of material that vaporizes in the evaporator. The refrigerator unit uses this energy flow as part of a cyclic system to keep foods cold. A new pallet of fruit with a mass of 500 kg is placed in the refrigerator. Assume that the specific heat of the fruit is the same as that of pure water because the fruit is mostly water. Describe how you would determine the mass of the working fluid that would have to be evaporated to lower the temperature of the fruit by 15C. List any information you would have to measure or look up.9.98 Hydrogen combines with oxygen in fuel cells according to the thermochemical equation 2H2(g)+O2(g)2H2O(g) H= -571.7 kJ Suppose that you are working with a firm that is using hydrogen fuel cells to power satellites. The satellite requires 4.0105 kJ of energy during its useful lifetime to stabilize its orbit. Describe how you would determine the mass of hydrogen you would need in your fuel cells for this particular satellite.9.99 The chemical reaction BBr3(g)+BCl3(g)BBr2Cl(g)+BCl2Br(g) , has an enthalpy change very close to zero. Using Lewis structures of the molecules, all of which have a central boron atom, provide a molecular-level description of why H for this reaction might be very small.9.100 Two baking sheets are made of different metals. You purchase both and bake a dozen cookies on each sheet at the same time in your oven. You observe that after 9 minutes, the cookies on one sheet are slightly burned on the bottom, whereas those on the other sheet are fine. (You are curious and you vary the conditions so you know the result is not caused by the oven.) (a) How can you use this observation to infer something about the specific heat of the materials in the baking sheets? (b) What is themathematical reasoning (equation) that you need to support your conclusion?9.101PAE 9.102 A runner generates 418 kJ of energy per kilometer from the cellular oxidation of food. The runner's body must dissipate this heat or the body will overheat. Suppose that sweat evaporation is the only important cooling mechanism. If you estimate the enthalpy of evaporation of water as 44 kJ/mol and assume that sweat can he treated as water, describe how you would estimate the volume of sweat that would have to be evaporated if the runner runs a 10-km race.9.103 One reason why the energy density of a fuel is important is that to move a vehicle one must also move its unburned fuel. Octane is a major component of gasoline. It burns according to the reaction 2C8H18(l)+25O2(g)16CO2(g)+18H2O(g) H = 1.10104 kJ Starting from this thermochemical equation, describe how you would determine the energy density, in kJ/g, for octane. Be sure to indicate what you would need to calculate or look up to complete this problem.9.104 An engineer is using sodium metal as a cooling agent in a design because it has useful thermal properties. Looting up the heat capacity, the engineer finds a value of 28.2 J mol-l °C-l. Carelessly, he wrote this number down without units. As a result, it was later taken as specific heat. (a) What would he the difference between these two values? (b) Would the engineer overestimate the ability of sodium to remove heat from the system or underestimate it because of this error? Be sure to explain your reasoning.9.105PAE 9.106PAE 9.107PAE 9.108PAE 9.109PAE 9.110PAE 1CO . explain the concept of entropy in your own words.3CO . state the second law of thermodynamics in words and equations and use it to predict spontaneity.5CO 6CO 7CO 8CO 9CO 10CO 10.1PAE 10.2PAE 10.3PAE 10.4PAE 10.5PAE Use the web to learn how many pounds of plastics are re cycled in your area each year. How has this value changed during the past decade?On the basis of your experience, predict which of the following reactions are spontaneous. (a) CO2(s)CO2(g) at 25°C (b) NaCl(s)NaCl(l) at 25°C (c) 2NaCl(s)2Na(s)+Cl2(g) (d) CO2(g)C(s)+O2(g)In the thermodynamic definition of a spontaneous process, why is it important that the phrase “continuous intervention” be used rather than just “intervention?”1f the combustion of butane is spontaneous, how can you carry a butane lighter safely in your pocket or purse?Identify each of the processes listed as spontaneous or nons-pontaneous. For each nonspontaneous process, describe the corresponding spontaneous process in the opposite direction. (a) A group of cheerleaders builds a human pyramid. (b) Table salt dissolves in water. (c) A cup of cold coffee in a room becomes steaming hot. (d) Water molecules in the air are converted to hydrogen and oxygen gases. (e) A person peels an orange, and you smell it from across the room.Identify each of the processes listed as spontaneous or non-spontaneous. For each non spontaneous process, describe the corresponding spontaneous process in the opposite direction. (a) Oxygen molecules dissociate to form oxygen atoms. (b) A tray of water is placed in the sun on a warm day and freezes. (c) A solution of salt water forms a layer of acid on top of a layer of base. (d) Silver nitrate is added to a solution of sodium chloride and a precipitate forms. (e) Sulfuric acid sitting in a beaker turns into water by giving off gaseous SO3.Athletic trainers use instant ice packs that can be cooled quickly on demand. Squeezing the pact breaks an inner container, allowing two components to mix and react. This reaction makes the pack become cold. Describe the heat flow for this spontaneous process.Are any of the following exothermic processes not spontaneous under any circumstances? (a) Snow forms from Liquid water. (b) Liquid water condenses from water vapor. (c) Fossil fuels burn to form carbon dioxide and water. (d) Monomers react to form a polymer.Enthalpy changes often help predict whether or not a process will be spontaneous. What type of reaction is more likely to be spontaneous: an exothermic or an endothermic one? Provide two examples that support your assertion and one counterexample.When a fossil fuel burns, is that fossil fuel the system? Explain your answer.Murphy's law is a whimsical rule that says that anything that can go wrong will go wrong. But in an article in the Journal of Chemical Education, Frank Lambert writes, "Murphy's law is a fraud." He also writes, "The second law of thermodynamics is time's arrow, but chemical kinetics is its clock." Read Lambert's article (J. Chem. Ed., 74(8), 1997, p. 947), and write an essay explaining, in the context of the latter quotation, why Lambert claims that Murphy's law is a fraud.10.17PAE Some games include dice with more than six sides. If you roll two eight-sided dice, with faces numbered one through eight, what is the probability of rolling two eights? What is the most probable roll?How does probability relate to spontaneity?10.20PAE For each pair of items, tell which has the higher entropy and explain why. (a) Item 1, a sample of solid CO2 at -78°C, or item 2, CO2 vapor at 0°C (b) Item I, solid sugar, or item 2, the same sugar dissolved in a cup of tea (c) Item 1, a 100-mL sample of pure water and a 100-mL sample of pure alcohol, or item 2, the same samples of water and alcohol after they have been poured together and stirred For each process, tell whether the entropy change of the system is positive or negative, (a) A glassblower heats glass (the system) to its softening temperature, (b) A teaspoon of sugar dissolves in a cup of coffee. (The system consists of both sugar and coffee.) (c) Calcium carbonate precipitates out of water in a cave to form stalactites and stalagmites. (Consider only the calcium carbonate to be the system.)Without doing a calculation, predict whether the entropy change will be positive or negative when each of the following reactions occurs in the direction it is written. (a) CH3OH(l)+3/2O2(g)CO2(g)+2H2O(g) (b) Br2(l)+H2(g)2HBr(g) (c) Na(s)+l/2F2(g)NaF(s) (d)CO(g)+2H2(g)CH3OH(l) (e) 2NH3(g)N2(g)+3H2(g)For the following chemical reactions, predict the sign of S for the system. (Note that this should not require any detailed calculations.) (a) Fe(s)+2HCl(g)FeCl2(s)+H2(g) (b) 3NO2(g)+H2O(l)2HNO3(l)+NO(g) (c)2K(s)+Cl2(g)2KCl(s) (d) Cl2(g)+2NO(g)2NOCl(g) (e) SiCl4(g)Si(s)+2Cl2(g)What happens to the entropy of the universe during a spontaneous process?10.26PAE One statement of the second law of thermodynamics is that heat cannot be turned completely into work. Another is that the entropy of the universe always increases. How are these two statements related?10.28PAE 10.29PAE Which reaction occurs with the greater increase in entropy? Explain your reasoning. (a) 2H2O(l)2H2(g)+O2(g) (b) C(s)+O2(g)CO2(g)Which reaction occurs with the greater increase in entropy? Explain your reasoning. (a) 2NO(g)N2(g)+O2(g) (b) Br2(g)+Cl2(g)2BrCl(g)Methanol is burned as fuel in some race cars. This makes it clear that the reaction is spontaneous once methanol is ignited. Yet the entropy change for the reaction 2CH3OH(l)+3O2(g)2CO2(g)+4H2O(l) is negative. Why doesn't this violate the second law of thermodynamics?Limestone is predominantly CaCO3, which can undergo the reaction CaCO3(s)CaO(s)+CO2(g). We know from experience that this reaction is not spontaneous, yet S for the reaction is positive. How can the second law of thermodynamics explain that this reaction is not spontaneous?Suppose that you find out that a system has an absolute entropy of zero. What else can you conclude about that system?Use tabulated thermodynamic data to calculate the standard entropy change of each of the reactions listed below. (a) Fe(s)+2HCl(g)FeCl2(s)+H2(g) (b)3NO2(g)+H2O(l)2HNO3(l)+NO(g) (c) 2K(s)+Cl2(g)2KCl(s) (d) Cl2(g)+2NO(g)2NOCl(g) (e) SiCl4(g)Si(s)+2Cl2(g)10.36PAE Calculate S for the dissolution of magnesium chloride: MgCl2(s)Mg2+(aq)+2Cl(aq) . Use your understanding of the solvation of ions at the molecular level to explain the sign of S .Calculate the standard entropy change for the reaction CO2(g)+2H2O(l)CH4(g)+2O2(g) . What does the sign of S say about the spontaneity of this reaction?Through photosynthesis, plants build molecules of sugar containing several carbon atoms from carbon dioxide. In the process, entropy is decreased. The reaction of CO2with formic acid to form oxalic acid provides a simple example of a reaction in which the number of carbon atoms in a compound increases: CO2(aq)+HCOOH(aq)H2C2O4(aq) (a) Calculate the standard entropy change for this reaction and discuss the sign of S . (b) How do plants carry out reactions that increase the number of carbon atoms in a sugar, given the changes in entropy for reactions like this?Find websites describing two different attempts to reach the coldest temperature on record. What features do these experiments have in common?10.41PAE 10.42PAE Under what conditions does G allow us to predict whether a process is spontaneous?There is another free energy state function, the Helmholtz free energy (A), defined as A = E — TS. Comparing this to the definition of G, we see that internal energy has replaced enthalpy in the definition. Under what conditions would this free energy tell us whether or not a process is spontaneous?10.45 Calculate G at 45°C for reactions for which (a) H = 293 kJ; S= -695 J/K (b) H= -1137 kJ; S = 0.496 kJ/K (c) H = -86.6 kJ; S = -382 J/K 10.46 Discuss the effect of temperature change on the spontaneity of the following reactions at 1 atm. (a) Al2O3(s)+2Fe(s)2Al(s)+Fe2O3(s) H = 851.5kJ; S =38.5 J/K (b) N2H4(l)N2(g)+2H2(g) H =-50.6 kJ; S= 0.3315 kJ/K (c) SO3(g)SO2(g)+12O2(g) H = 98.9 kJ; S= 0.0939 kJ/K The reaction CO2(g)+H2(g)CO(g)+H2O(g) is not spontaneous at room temperature but becomes spontaneous at a much higher temperature. What can you conclude from this about the signs of H and S , assuming that the enthalpy and entropy changes are not greatly affected by the temperature change? Explain your reasoning.10.48PAE 10.49PAE For the reaction NO(g)+NO2(g)N2O3(g) , use tabulated thermodynamic data to calculate H and S. Then use those values to answer the following questions. (a) Is this reaction spontaneous at 25°C? Explain your answer. (b) If the reaction is not spontaneous at 25°C, will it become spontaneous at higher temperatures or lower temperatures? (c) To show that your prediction is accurate, choose a temperature that corresponds to your prediction in part (b) and calculate G . (Assume that both enthalpy and entropy are independent of temperature.)10.51 The combustion of acetylene was used in welder's torches for many years because it produces a very hot flame: C2H2(g)+52O2(g)2CO2(g)+H2O(g) H= -1255.5 kJ (a) Use data in Appendix E to calculate S for this reaction, (b) Calculate G and show that the reaction is spontaneous at 25°C. (c) Ls there any temperature range in which this reaction is not spontaneous? (d) Do you think you could use Equation 10.4 to calculate such a temperature range reliably? Explain your answer.Natural gas (methane) is being used in experimental vehicles as a clean-burning fuel. (a) Write the equation for the combustion of CH4(g), assuming that all reactants and products are in the gas phase. (b) Use data from Appendix E to calculate S for this reaction. (c) Calculate G and show that the reaction is spontaneous at 25°C.Silicon forms a series of compounds analogous to the al-kanes and having the general formula SinH2n+2. The first of these compounds is silane, SiH4, which is used in the electronics industry to produce thin ultrapure silicon films. SiH4(g) is somewhat difficult to work with because it is py-ropboric at room temperature—meaning that it bursts into flame spontaneously when exposed to air. (a) Write an equation for the combustion of SiH4(g). (The reaction is analogous to hydrocarbon combustion, and SiO2 is a solid under standard conditions. Assume the water produced will be a gas.) (b) Use the data from Appendix E to calculate ? for this reaction. (c) Calculate G and show that the reaction is spontaneous at 25°C. (d) Compare G for this reaction to the combustion of methane. (See the previous problem.) Are the reactions in these two exercises enthalpy or entropy driven? Explain.Explain why Gf of O2 (g) is zero.Using tabulated thermodynamic data, calculate G for these reactions. (a) Fe(s)+2HCl(g)FeCl2(s)+H2(g) (b) 3NO2(g)+H2O(l)2HNO3(l)+NO(g) (c) 2K(s)+Cl2(g)2KCl(s) (d) Cl2(g)+2NO(g)2NOCl(g) (e) SiCl4(g)Si(s)+2Cl2(g)Using tabulated thermodynamic data, calculate G for these reactions. (a) Mg3N2(s)+6H2O(l)2NH3(g)+3Mg(OH)2(s) (b) 4CH3NH2(g)+9O2(g)4CO2(g)+10H2O(l)+2N2(g) (c) Fe3O(s)+4CO(g)3Fe(s)+4CO2(g) (d) P4O10(s)+6H2O(l)4H3PO4(aq)Calculate G for the dissolution of both sodium chloride and silver chloride using data from Appendix E. Explain how the values you obtain relate to the solubility rules for these substances.Phosphorus exists in multiple solid phases, including two known as red phosphorus and white phosphorus. (a) Based on their respective heats of formation, which form of phosphorus is defined as the standard state? (b) Now consider the phase transition between white and red phosphorous: P4(s, white4 P(s, red). Use data from Appendix E to determine which form of phosphorous is actually more stable at 25C. (Your result should reveal that phosphorus is an exception to the usual convention for defining the standard state.) (c) Is the same form of the solid more stable at all temperatures? If not, what temperatures are needed to make the other form more stable?10.59 The normal melting point of benzene, C6H6, is 5.5°C. For the process of melting solid benzene, what is the sign of each of the following? (a) H, (b) S, (c) Gat 5.5°C, (d) Gat 0.0°C, (e) Gat 25.0°C.10.60PAE Estimate the temperature range over which each of the following reactions is spontaneous. (a) 2Al(s)+3Cl2(g)2AlCl3(s) (b) 2NOCl(g)2NO(g)+Cl2(g) (c) 4NO(g)+6H2O(g)4NH3(g)+5O2(g) (d) 2PH3(g)3H2(g)+2P(g)Recall that incomplete combustion of fossil fuels occurs when too little oxygen is present and results in the production of carbon monoxide rather than carbon dioxide. Water is the other product in each case. (a) Write balanced chemical equations for the complete and incomplete combustion of propane. (b) Using these equations, predict which will have the larger change in entropy. (c) Use tabulated thermodynamic data to calculate G for each reaction. (d) Based on these results, predict the sign and value of G for the combustion of carbon monoxide to form carbon dioxide.During polymerization, the system usually becomes more ordered as monomers link together. Could an endothermic polymerization reaction ever occur spontaneously? Explain.10.64PAE 10.65PAE The recycling of polymers represents only one industrial process that allows creating order in one location by creating greater disorder at some other location, often at a power plant. List three other industrial processes that must create disorder in the surroundings to generate the desired material.10.67PAE When ice melts, its volume decreases. Despite this fact, the entropy of the system increases. Explain (a) why the entropy increases and (b) why under most circumstances, a decrease in volume results in an entropy decrease.10.69 If a sample of air were separated into nitrogen and oxygen molecules (ignoring other gases present), what would be the sign of for this process? Explain your answer. The next four questions relate to the following paragraph [Frank L. Lambert, Journal of Chemical Education, 76(10), 1999, 1385]. "The movement of macro objects from one location to another by an external agent involves no change in the objects' physical (thermodynamic) entropy. The agent of movement undergoes a thermodynamic entropy increase in the process."10.70PAE An explosion brings down an old building, leaving behind a pile of rubble. Does this cause a thermodynamic entropy increase? If so, where? Write a paragraph explaining your reasoning.10.72PAE 10.73PAE 10.74PAE 10.75PAE Some say that the job of an engineer is to fight nature and the tendencies of entropy. (a) Does this statement seem accurate in any way? (b) How can any engineering design create order without violating the second law of thermodynamics?A beaker of water at 40C (on the left in the drawing) and a beaker of ice water at 0°C are placed side by side in an insulated container. After some time has passed, the temperature of the water in the beaker on the left is 30°C and the temperature of the ice water is still 0°C. Describe what is happening in each beaker (a) on the molecular level and (b) in terms of the second law of thermodynamics Why is it usually easier to use G to determine the spontaneity of a process rather than Su ?The molecular scale pictures below show snapshots of a strong acid at three different instants after it is added to water. Place the three pictures in the correct order so that they show the progress of the spontaneous process that takes place as the acid dissolves in the water. Explain your answer in terms of entropy 10.80PAE Diethyl ether is a liquid at normal temperature and pressure, and it boils at 35 C. Given that H is 26.0 kJ/mol for the vaporization of diethyl ether, find its molar entropy change for vaporization.Calculate the entropy change, S , for the vaporization of ethanol, C2H5OH, at the boiling point of 78.3C. The heat of vaporization of the alcohol is 39.3 kJ/mol. C2H5OH(l)C2H5OH(g) S= ?Gallium metal has a melting point of 29.8°C. Use the information below to estimate the boiling point of gallium in °C. For a metal, gallium has a very low melting point. Substance Hf (kJ mol-1) Gf (kJ mol-1) S (J mol-1 K-1) Ga(s) 0 0 40.83 Ga( l ) 5.578 0.0888 59.25 Ga(g) 271.96 233.76 169.03 Methane can be produced from CO and H2.The process might be done in two steps, as shown below, with each step carried out in a separate reaction vessel within the production plant. Reaction 1 CO(g)+2H2(g)CH3OH(l) S = -532 J/K Reaction 2 CH3OH(l)CH4(g)+12O2(g) S= +162 J/K NOTE: You should be able to work this problem without using any additional tabulated data. (a) Calculate H for reaction 1. (b) Calculate Gf for CO(g). (c) Calculate S° for O2(g). (d) At what temperatures is reaction 1 spontaneous? (e) Suggest a reason why these two steps would need to be carried out separately. Substance Hf (kJ mol-1) Gf (kJ mol-1) S (J mol-1 K-1) CO(s) -110.5 197.674 CH3OH( l ) -238.7 -166.4 126.8 CH4(g) -74.8 186.2 10.85 Iodine is not very soluble in water, but it dissolves readily in a solution containing iodide ions by the following reaction: I2(aq)+I(aq)I3(aq) The following graph shows the results of a study of the temperature dependence of G for this reaction. (The solid line is a best fit to the actual data points.) Notice that the quantity on the y axis is G/T , not just G. Additional data relevant to this reaction are also given in the table that follows the graph. (a) Calculate G for this reaction at 298 K. (DO NOT read this value off the graph. Use the data given to calculate a more accurate value.) (b) Determine H for this reaction. Assume that H is independent of T. (HINT: You will need to use the graph provided to find H . It may help if you realize that the graph is a straight line and then try to write an equation for that line The enthalpy of vaporization for water is 40.65 kJ mol-1. As a design engineer for a project in a desert climate, you are exploring the option of using evaporative cooling. (a) If the air has an average volumetric heat capacity of 0.00130 J cm-3 K-1, what is the minimum mass of water that would need to evaporate in order to cool a 5 m? 5 m room with a 3 m ceiling by 5°F using this method? (b) Is this a spontaneous or nonspontaneous process?Determine whether each of the following statements is true or false. If false, modify to make the statement true. (a) An exothermic reaction is spontaneous. (b) When G is positive, the reaction cannot occur under any conditions. (c) S is positive for a reaction in which there is an increase in the number of moles. (d) If H and S are both negative, G will he negative.Nickel metal reacts with carbon monoxide to form tetra-carbonyl nickel, Ni(CO)4: Ni(s)+4CO(g)Ni(CO)4(g) This reaction is exploited in the Mond process in order to separate pure nickel from other metals. The reaction above separates nickel from impurities by dissolving it into the gas phase. Conditions are then changed so that the reaction runs in the opposite direction to recover the purified metal. (a) Predict the sign of S for the reaction as written above. (b) Use tabulated thermodynamic data to calculate H, S , and G for the reaction. (c) Find the range of temperatures at which this reaction is spontaneous in the forward direction.Polyethylene has a heat capacity of 2,3027 J g-1 °C-1. You need to decide if 1.0 ounce of polyethylene can be used to package a material that will be releasing heat when in use. Consumer safety specifications indicate that the maximum allowable temperature for the polyethylene is 45C. It can be assumed that the plastic is initially at room temperature. (a) What temperature will the polyethylene reach if the product generates 1500 J of heat and all of this energy is absorbed by the plastic package? (b) Is this a realistic estimate of the temperature that the polyethylene packaging would reach? Explain your answer. (c) What is the enthalpy change of the polyethylene? (d) Estimate the entropy change of the polyethylene. (You will need to assume that the temperature of the plastic is constant.)A key component in many chemical engineering designs is the separation of mixtures of chemicals. (a) What happens to the entropy of the system when a chemical mixture is separated? (b) Are designs for chemical separation more likely to rely on spontaneous or nonspontaneous processes?The reaction shown below is involved in the refining of iron. (The table that follows provides all of the thermodynamic data you should need for this problem.) 2Fe2O3(s)+3C(s,graphite)4Fe(s)+3CO2(g) (a) Find H for the reaction. (b) S for the reaction above is 557.98 J/K. Find S° for Fe2O3(s). (c) Calculate G for the reaction at the standard temperature of 298 K. (There are two ways that you could do this.) (d) At what temperatures would this reaction be spontaneous? Compound Hf (kJ mol-1) S° (kJ mol-1) Gf (J mol-1 K-1) Fe2O3(s) -824.2 ? -742.2 C(s, graphite) 0 5.740 0 Fe(s) 0 27.3 0 CO2(g) -393.5 213.6 -394.4.83 Using only the data given below, determine G for the following reaction: NO(g)+O(g)NO2(g) (Remember that G is a state function, just like H .) 2O3(g)3O2(g)G = -326 kJ O2(g)2O(g)G = 463.6 kJ NO(g)+O3(g)NO2(g)+O2(g)G = -198.3 kJ The graph below shows G as a function of temperature for the synthesis of ammonia from nitrogen and hydrogen. N2(g)+3H2(g)2NH3(g) a) Use the graph to estimate S for the ammonia synthesis reaction. (b) Given that the standard free energy change of formation for ammonia ( Gf ) is -16.50 kJ/mol, estimate H for the ammonia synthesis reaction.10.94PAE 10.95PAE 10.96PAE 10.97PAE 10.98PAE Thermodynamics provides a way to interpret everyday occurrences. If you live in northern climates, one common experience is that during early winter, snow falls but then melts when it hits the ground. Both the formation and the melting happen spontaneously. How can thermodynamics explain both of these seemingly opposed events?10.100PAE 10.101 Fluorine reacts with liquid water to form gaseous hydrogen fluoride and oxygen. (a) Write a balanced chemical equation for this reaction. (b) Use tabulated data to determine the free energy change for the reaction and comment on its spontaneity. (c) Use tabulated data to calculate the enthalpy change of the reaction. (d) Determine how much heat flows and in what direction when 34.5 g of fluorine gas is bubbled through excess water.10.102 Ammonia can react with oxygen gas to form nitrogen dioxide and water. (a) Write a balanced chemical equation for this reaction. (b) Use tabulated data to determine the free energy change for the reaction and comment on its spontaneity. (c) Use tabulated data to calculate the enthalpy change of the reaction, (d) Determine how much heat flows and in what direction when 11.4 g of ammonia gas is burned in excess oxygen.10.103PAE 10.104 (a) When a chemical bond forms, what happens to the entropy of the system? (b) Thermodynamically, what allows any bond formation to occur? (c) What do your answers to parts (a) and (b) suggest must be true about the formation of chemical bonds for the octet rule to hold?1CO . define the rate of a chemical reaction and express the rate in terms of the concentrations of individual reactants or products.3CO 4CO . explain the difference between elementary reactions and multistep reactions.. find the rate law predicted for a particular reaction mechanism.. use a molecular perspective to explain the significance of the terms in the Arrhenius equation.8CO . explain the role of a catalyst in the design of practical chemical reactions.11.1PAE List two types of chemical compounds that must be present in the air for photochemical smog to form. What are the most common sources of these compounds?11.3PAE 11.4PAE 11.5PAE 11.6PAE Asphalt is composed of a mixture of organic chemicals. Does an asphalt parking lot contribute directly to the formation of photochemical smog? Explain your answer.11.8PAE 11.9PAE

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