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xtra_probs_wk2 - Extra Problems for Chapter 6 9.10 13.5 and...

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Unformatted text preview: Extra Problems for Chapter 6, 9.10, 13.5, and 13.9 1. A 1 .0— liter sample of a gas is adiabatically expanded against a constant external pressure of 1.0 atm until the volume has increased to 10.0 liter. ' a) What 1s the work? [-910 J] b) Determine the change in internal energy of the system. , . [-910 J] 0) Calculate the change in internal energy of the surroundings. [910 J] 2. Consider the molecule, ethanol CH3 CH20H(l) a) Write the equation whose enthalpy change defines the enthalpy of combustion of ethanol, AHcomb' b) Write the equation whose enthalpy change defines the standard enthalpy of formation of ethanol, AH 19 c) Write the equation whose enthalpy change defines the enthalpy of vaporization of . ethanol, AHvap. d) Write the equation whose enthalpy change defines the bond enthalpy of ethanol. 3. A styrofoam—cup calorimeter containing 150 g of water is calibrated by generating 1770 J of heat within it. The temperature increases by 1.67°C. c,(H20) = 4.184 J g'1 K—1 a) What is the calorimeter constant (heat capacity of the calorimeter)? [432 J K '1] b) What assumptions(s) are you making in order to do the calculation of part a)? -2- 4. One mole of argon gas is held in a rigid container whose volume is 22.41 L at 273.15 K. 3000 k] of heat is added. cV = 12.47 J mol'1 K”1 a) What is the initial pressure of the gas? [1.000 atm] b) What is qsys? [3.000 kJ] c) What is wsys? _ [0] d) What is the final temperature of the gas? [513.7 K] e) What is the final pressure of the gas? [1.881 atm] D What is AE? [3.000 kJ] g) What is AH ? [5.001 kJ] h) 3 k] of heat was added but AH > 3 kJ. Why does this not violate the Law of Conserva- tion of Energy? -3- 5. 0.1584 g of solid benzoic acid (C6H5COOH) are combusted in a constant volume bomb calorimeter at 25°C. The temperature rises by 254°C. AE for the combustion of benzoic acid is -26.38 kJ g'l. a) Write a balanced chemical equation for the combustion. b) Calculate the heat capacity of the calorimeter. [1.65 k] K'l] c) Give the value of AE for the combustion in kJ mol'l. [—3222 kJ mol‘l] (1) Estimate the value of AH for the combustion in kJ mol'l. [-3223 k] mol‘l] e) Estimate the standard enthalpy of formation of benzoic acid in kJ mol'l. [—389 kJ mol'l] -4- 6. Determine the standard enthalpy of formation of Fe203 (s) from the following data 2 Fe(s) + 3 CO(g) —-9 F6203(S) + 3 C(gr) AH ° = —489.8 kJ 2 CO(g) + 02(g) —> 2 C02(g) -565.1kJ C(gr) + 02(g) —> C02(g) ‘ " , , —393.5'1 kJ [-822.7 M] 7. How much hot iron at 430°C must be added to 50 g of snow at —15°C to bring the final tem- perature of the mixture to 30°C? Assume that there is no heat loss to the surroundings, cs(Fe,s) = 0.449 J g-1 K‘l, cs(H20,s) = 2.09 J g'1 K'l, cs(H20,l) = 4.18 J g'1 K'l, ~ AHqu(H20) = 334 J g‘l. [140 g] 8. The normal melting point of table salt, NaCl(s), is 800°C. How much heat is given off if 100 g of molten salt at 800°C were to solidify and cool to 25°C? For NaCl: AHfi,S = 490 J g‘l, AHvap = 2990 J g‘l, and cs(s) = 0.8506 J g—1 K‘l. {-115 kJ] 9. AH? for CH4(g) is —74.81 kJ mol'l. a) What is AH° for CH4(g) + 202(g) —> C02(g) + 2H20(l) . {-890.36 kJ] b) Is the above reaction exothermic or endothermic? Explain ' 10. For the combustion of ethanol CH3CH20H(l) + 02(g) —> C02(g_) + H200) a) Balance the equation. I b) Calculate the standard enthalpy change. [-1366.28 kJ] 0) Determine AE°. [—1364.34 kJ] (1) Calculate the work done by the reaction. [—2479.0 J] e) At 25°C, AHvap(H20) = 44.01 kJ mol‘1 and AHvap(CH3CH20H) = 42.59 kJ mol"1. What is AH ° for the combustion of ethanol when all reactants and products are gases? [-1277.38 kJ mol‘l] 11. 12. 13. 14. —6— The standard enthalpy of formation of carbon tetrachloride, CC14(g) is -102.9 kJ mol"1. The standard enthalpies of formation of C and Cl, atomization enthalpies, are 716.682 and 121.68 kJ mol’l, respectively. a) Write the chemical reaction whose enthalpy change is AH? of CC14(g). b) Write the reaction from whose enthalpy change the average bond enthalpy of CCl4(g) can be obtained. ' c) Determine the average bond enthalpy of CCl4(g). [326.58 kJ mol‘l]. Write a balanced equation for the conversion of methane (CH4) to ethane (C2116) and hydro— gen, all as gases and use the table of bond enthalpies to estimate the enthalpy change for the above reaction. ‘ [42 kJ] For the reaction 2H2(g) + 02(g) —> 2H20(g) AH ° = —484 kJ. The average bond enthalpies of H2 and ‘02 are 436 and 498 kJ mol’l, respectively. Determine the bond enthalpy of the OH bond in kJ mol‘l. [464 kJ mol‘l] Determine the standard enthalpy of formation of ammonia, NH3 (g). The average bond enthalpy of an N—H bond is 391 kJ mol‘l. The standard enthalpies of formation of N(g) and H(g), atomization enthalpies, are 472.70 and 217.96 1d mol'l, respectively. [-46 kJ mol‘l] -7- Potentially Useful Information PV = nRT ‘_ qV = AE (with only PV work) q = CAT qP = AH (with only PV work) AE = q + w _ w = ~PextAV (PV work) H = E + PV R = 8.314472 J mol'1 K’1 = 0.082057 L atm mol‘l K‘1 P =1atm = 760 mm Hg = 1.01325 bar K = °C + 273.15 SELECTED STANDARD ENTHALPIES OF FORMATION (kJ/mol) CH3CH20H(aq) -288.3 CH3CH20H(l) , -277.0 VCH3CH20H(g) —235.3 H20(l) -285.83 H20(g) —241.83 002(8) -393.509 C(g) 716.67 H(g) 217.965 0(g) 249.170 ...
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