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Selected Solutions Manual for Chemistry: Structure and Properties
- The standard molar enthalpy of formation of diborane, B2H6(g), cannot be determined directly because the compound cannot be prepared by the reaction of boron and hydrogen. It can be calculated from other enthalpy changes, however. The following enthalpy changes can be measured. 4 B(s) + 3 O2(g) 2 B2O3(s) rH = 2543.8 kJ/mol-rxn H2(g) + O2(g) H2O(g) rH = 241.8 kl/mol-rxn B2H6(g) + 3 O2(g) B2O3(s) + 3 H2O(g) rH = 2032.9 kJ/mol-rxn (a) Show how these equations can be added together to give the equation for the formation of B2H6(g) from B(s) and H2(g) in their standard states. Assign enthalpy changes to each reaction. (b) Calculate fH for B2H6(g). (c) Draw an energy level diagram that shows how the various enthalpies in this problem are related. (d) Is the formation of B2H6(g) from its elements exo- or endothermic?arrow_forwardThe 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.arrow_forwardNatural gas companies in the United States use the therm as a unit of energy. One therm is 1105 BTU. (a) How many joules are in one therm? (1J=9.48104BTU) (b) When propane gas, C3H8, is burned in oxygen, CO2 and steam are produced. How many therms of energy are given off by 1.00 mol of propane gas?arrow_forward
- The initial temperature of a 344-g sample of iron is 18.2 C. If the sample absorbs 2.25 kJ of energy as heat, what is its final temperature?arrow_forwardWhich of the following substances have an enthalpy of formation equal to zero? a. Cl2(g) b. H2(g) c. N2(l) d. Cl(g)arrow_forwardThe complete combustion of acetylene, C2H2(g), produces 1300. kJ of energy per mole of acetylene consumed. How many grams of acetylene must be burned to produce enough heat to raise the temperature of 1.00 gal water by 10.0c if the process is 80.0% efficient? Assume the density of water is 1.00 g/cm3arrow_forward
- Insoluble PbBr2(s) precipitates when solutions of Pb(NO3)2(aq) and NaBr(aq) are mixed. Pb(NO3)2(aq) + 2 NaBr(aq) PbBr2(s) + 2 NaNO3(aq) rH = ? To measure the enthalpy change, 200. mL. of 0.75 M Pb(NO3)2(aq) and 200. mL of 1.5 M NaBr(aq) are mixed in a coffee-cup calorimeter. The temperature of the mixture rises by 2.44 C. Calculate the enthalpy change for the precipitation of PbBr2(s), in kJ/mol. (Assume the density of the solution is 1.0 g/mL., and its specific heat capacity is 4.2 J/g K.)arrow_forwardThe “Chemistry in Focus” segment Nature Has Hot Plants discusses thermogenic, or heat-producing, plants. For some plants, enough heat is generated to increase the temperature of the blossom by 15 °C. About how much heat is required to increase the temperature of 1 L of water by 15 °C?arrow_forwardSalicylic acid, C7H6O3, is one of the starting materials in the manufacture of aspirin. When 1.00 g of salicylic acid burns in a bomb calorimeter, the temperature of the bomb and water goes from 23.11C to 28.91C. The calorimeter and water absorb 21.9 kJ of heat. How much heat is given off when one mole of salicylic acid burns?arrow_forward
- Quinone is an important type of molecule that is involved in photosynthesis. The transport of electrons mediated by quinone in certain enzymes allows plants to take water, carbondioxide, and the energy of sunlight to create glucose. A 0.1964-g sample of quinone (C6H4O2) is burned in a bomb calorimeter with a heat capacity of 1.56 kJ/C. The temperature of the calorimeter increases by 3.2C. Calculate the energy of combustion of quinone per gram and per mole.arrow_forwardClassify each process as exothermic or endothermic. (a) ice melts (b) gasoline burns (c) steam condenses (d) reactants products, H = 50 kJarrow_forwardYou have two samples of different metals, metal A and metal B, each having the same mass. You heat both metals to 95C and then place each one into separate beakers containing the same quantity of water at 25C. a You measure the temperatures of the water in the two beakers when each metal has cooled by 10C and find that the temperature of the water with metal A is higher than the temperature of the water with metal B. Which metal has the greater specific heat? Explain. b After waiting a period of time, the temperature of the water in each beaker rises to a maximum value. In which beaker does the water temperature rise to the higher value, the one with metal A or the one with metal B? Explain.arrow_forward
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