A student dissolves 12.3 g of ammonium nitrate (NH, NO,) in 300. g of water in a well-insulated open cup. She then observes the temperature of the water fall from 22.0 °C to 18.4 °C over the course of 8.1 minutes. Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction: NH,NO, (s) NH (aq) + NO, (aq) You can make any reasonable assumptions about the physical properties of the solution. Be sure answers you calculate using measured data are rounded to 2 significant digits. Note for advanced students: it's possible the student did not do the experiment carefully, and the values you calculate may not be the same as the known and published values for this reaction. O exothermic Is this reaction exothermic, endothermic, or neither? O endothermic O neither If you said the reaction was exothermic or endothermic, calculate the amount of heat that was released or absorbed by the reaction in this case. | kJ kJ Calculate the reaction enthalpy AHvn per mole of NH¼NO3: mol

A student dissolves 12.3 g of ammonium nitrate (NH, NO,) in 300. g of water in a well-insulated open cup. She then observes the temperature of the water fall from 22.0 °C to 18.4 °C over the course of 8.1 minutes. Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction: NH,NO, (s) NH (aq) + NO, (aq) You can make any reasonable assumptions about the physical properties of the solution. Be sure answers you calculate using measured data are rounded to 2 significant digits. Note for advanced students: it's possible the student did not do the experiment carefully, and the values you calculate may not be the same as the known and published values for this reaction. O exothermic Is this reaction exothermic, endothermic, or neither? O endothermic O neither If you said the reaction was exothermic or endothermic, calculate the amount of heat that was released or absorbed by the reaction in this case. | kJ kJ Calculate the reaction enthalpy AHvn per mole of NH¼NO3: mol

Principles of Modern Chemistry

8th Edition

ISBN:9781305079113

Author:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler

Publisher:David W. Oxtoby, H. Pat Gillis, Laurie J. Butler

Chapter12: Thermodynamic Processes And Thermochemistry

Section: Chapter Questions

Problem 42P

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Suppose that you are studying kinetic energy of helium molecules: A helium weather balloon rises to an altitude of 40,000 ft; the temperature of the gas drops to 70 F. (a) Make an appropriate choice of system and surroundings and describe it unambiguously. (b) Explain why you chose the system and surroundings you did. (c) Identify transfers of energy and material into and out of the system that would be important for you to monitor in your study.
A piece of chocolate cake contains about 400 calories. A nutritional calorie is equal to 1000 calories (thermochemical calories), which is equal to 4.184 kJ. How many 8-in-high steps must a 180-lb man climb to expend the 400 Cal from the piece of cake? See Exercise 28 for the formula for potential energy.
Solid ammonium chloride is added to water in a beaker and dissolves. The beaker becomes cold to the touch. Make an appropriate choice of system and surroundings and describe it unambiguously. Explain why you chose the system and surroundings you did. Identify transfers of energy and material into and out of the system that would be important for you to monitor in your study. Is the process of dissolving NH4Cl(s) in water exothermic or endothermic? Explain your answer.
The formation of aluminum oxide from its elements is highly exothermic. If 2.70 g Al metal is burned in pure O2 to give A12O3, calculate how much thermal energy is evolved in the process (at constant pressure).
The temperature of the cooling water as it leaves the hot engine of an automobile is 240 F. After it passes through the radiator it has a temperature of 175 F. Calculate the amount of heat transferred from the engine to the surroundings by one gallon of water with a specific heat of 4.184 J/g oC.
It has been determined that the body can generate 5500 kJ of energy during one hour of strenuous exercise. Perspiration is the body’s mechanism for eliminating this heat. How many grams and how many liters of water would have to be evaporated through perspiration to rid the body of the heat generated during two hours of exercise? (The heat of vaporization of water is 40.6 kJ/mol.)
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?
Magnesium sulfate is often used in first-aid hot packs, giving off heat when dissolved in water. A coffee-cup calorimeter at 25C contains 15.0 mL of water at 25C. A 2.00-g sample of MgSO4 is dissolved in the water and 1.51 kJ of heat are evolved. (You can make the following assumptions about the solution: volume=15.0 mL, density=1.00 g/mL, specific heat=4.18J/gC.) (a) Write a balanced equation for the solution process. (b) Is the process exothermic? (c) What is qH2O? (d) What is the final temperature of the solution? (e) What are the initial and final temperatures in F?
In the 1880s, Frederick Trouton noted that the enthalpy of vaporization of 1 mol pure liquid is approximately 88 times the boiling point, Tb, of the liquid on the Kelvin scale. This relationship is called Troutons rule and is represented by the thermochemical equation liquid gas H = 88 Tb, joules Combined with an empirical formula from chemical analysis, Troutons rule can be used to find the molecular formula of a compound, as illustrated here. A compound that contains only carbon and hydrogen is 85.6% C and 14.4% H. Its enthalpy of vaporization is 389 J/g, and it boils at a temperature of 322 K. (a) What is the empirical formula of this compound? (b) Use Troutons rule to calculate the approximate enthalpy or vaporization or one mole of the compound. Combine the enthalpy of vaporization per mole with that same quantity per gram to obtain an approximate molar mass of the compound. (c) Use the results of parts (a) and (b) to find the molecular formula of this compound. Remember that the molecular mass must be exactly a whole-number multiple of the empirical formula mass, so considerable rounding may be needed.
A piece of lead of mass 121.6 g was heated by an electrical coil. From the resistance of the coil, the current, and the Time the current flowed, it was calculated that 235 J of heat was added to the lead. The temperature of the lead rose from 20.4C to 35.5C. What is the specific heat of the lead?
As the gas trapped in a cylinder with a movable piston cools, 1.34 kJ of work is done on the gas by the surroundings. If the gas is at a constant pressure of 1.33 105 Pa, what is the change of volume (in L) of the gas?
For each of the following processes, predict the algebraic sign of rH, rS, and rG. No calculations are necessary; use your common sense. (a) The decomposition of liquid water to give gaseous oxygen and hydrogen, a process that requires a considerable amount of energy. (b) Dynamite is a mixture of nitroglycerin, C3H5N3O9, and diatomaceous earth. The explosive decomposition of nitroglycerin gives gaseous products such as water, CO2, and others; much heat is evolved. (c) The combustion of gasoline in the engine of your car, as exemplified by the combustion of octane. 2 C8H18(g) + 25 O2(g) 16 CO2(g) + 18 H2O(g)

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