Chapter 5 Practice Multiple Choice & Free

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1 Name Response 1. A system has an increase in internal energy, E, of 40 kj. If 20 kj of work, w, is done on the system, what is the heat change, q? a) +60 kj d) -20 kj b) +40 kj e) -60 kj c) +20 kj 2. Which equation represents the heat of formation, Hf, for MgCl2? a) Mg 2+ (aq) + 2 Cl MgCl2(s) b) Mg(s) + 2 Cl(g) MgCl2(s) c) MgCl2(s) Mg 2+ (aq) + 2 Cl (aq) d) Mg(s) + Cl2(g) MgCl2(s) 3. The correct units for specific heat capacity: a) J/ C c) J/g C b) J/g d) C/g Chapter 5 Practice Multiple Choice & Free 5. Using the H f given below, calculate the H combustion for propane, C 3 H 8. H f (kj/mol) H 2 O(l) -286 CO 2 (g) -394 C 3 H 8 (g) -104 a) 576 kj c) kj b) -576 kj d) kj 6. The heat of vaporization of methane, CH 4, at its boiling point is 9.20 kj/mol. How much heat energy is required to vaporize 90. g of methane at its boiling point? a) 1380 kj c) 21.6 kj b) 86.3 kj d) 51.8 kj 4. How much heat is required to convert solid sulfur to gaseous sulfur at 298 K and 1 atm pressure? H (kj/mol) S(s) + O2(g) SO2(g) 395 S(g) + O2(g) SO2(g) 618 a) 1013 kj/mol c) +223 kj/mol b) 223 kj/mol d) +618 kj/mol 7. How much energy is required to melt 39.0 g benzene, C 6 H 6 (MM = 78 g/mol)? The heat of fusion of benzene is 2.37 kj/mol. a) 1.19 kj c) 1850 kj b) 23.7 kj d) kj

2 8. If H for a reaction is positive, a) the reaction rate is generally very fast. b) the enthalpy change of the reverse reaction is positive. c) the enthalpy of the products is greater than the enthalpy of the reactants. d) the energy released during bond formation is greater than the energy absorbed during bonding breaking for the reaction. 9. Given the two equations: 13. Calculate the standard enthalpy of the reaction for the process 3NO(g) N 2 O(g) + NO 2 (g) using the standard enthalpies of formation (in kj/mol): NO = 90; N 2 O = 82.1; NO 2 = 34.0 a) kj c) kj b) 206 kj d) 386 kj 2 S(s) + 3 O2(g) 2 SO3(g) H = kj SO2(g) + 1 / 2 O2(g) SO3(g) H = 99.1 kj What is the standard enthalpy of formation for sulfur dioxide, SO2(g)? a) kj c) kj b) kj d) kj 10. When g benzoic acid (HC 6 H 4 CO 2 ) and excess oxygen is ignited in a bomb calorimeter, the temperature of the water changes from C to C. The heat capacity of the calorimeter is 603 J/ C. What is the E for this reaction? a) -597 J c) -136 J b) J d) -149 J 14. How much energy is required to change the temperature of 2.00 g aluminum from 20.0 C to 25.0 C? The specific heat of aluminum is J/g C. a) 2.3 J c) 0.36 J b) 9.0 J d) J 15. Calculate the amount of heat needed to change 20.0 g ice at 0 C to water at 0 C. The heat of fusion of H 2 O = 333 J/g; a)56.5 kj c) 7.06 kj b) 6.66 kj d) 463 kj 11. Under conditions of constant pressure, the heat change that occurs during a chemical reaction is equal to a) H c) T b) E d) P 12. Which one of the following would have an enthalpy of formation value ( H f ) of zero? a) H 2 O(g) c) H 2 O(l) b) O(g) d) O 2 (g) 1. C 2. D 3. C 4. C 5. C 6. D 7. A 8. C 9. B 10. C 11. A 12. D 13. A 14. B 15. B

3 Free Response Practice 1995 B Propane, C 3 H 8, is a hydrocarbon that is commonly used as fuel for cooking. (a) Write a balanced equation for the complete combustion of propane gas, which yields CO 2 (g) and H 2 O(l). (b) Calculate the volume of air at 30 o C and 1.00 atmosphere that is needed to burn completely 10.0 grams of propane. Assume that air is 21.0 percent O 2 by volume. (c) The heat of combustion of propane is -2,220.1 kj/mol. Calculate the heat of formation, ΔH( o f), of propane given that ΔH( o f) of H 2 O(l) = kj/mol and ΔH( o f) of CO 2 (g) = kj/mol. (d) Assuming that all of the heat evolved in burning 30.0 grams of propane is transferred to 8.00 kilograms of water (specific heat = 4.18 J/g. K), calculate the increase in temperature of water. ` 6.90.Z Given the following data, Fe 2 O 3 (s) + 3CO (g) 2Fe (s) + 3CO 2 (g) 3Fe 2 O 3 (s) + CO (g) 2Fe 3 O 4 (s) + CO 2 (g) Fe 3 O 4 (s) + CO (g) 3FeO (s) + CO 2 (g) ΔH o = -23 kj ΔH o = -39 kj ΔHo = +18 kj Calculate ΔH o for the reaction FeO (s) + CO (g) Fe (s) + CO 2 (g)

4 1979 B ΔH f o S o Compound (kilocalories/mole) (calories/mole K) H 2 O(l) CO 2 (g) O 2 (g) C 3 H 8? 64.5 When gram of propane gas, C 3 H 8, is burned at 25 o C and 1.00 atmosphere, H 2 O(l) and CO 2 (g) are formed with the evolution of kilocalories. (a) Write a balanced equation for the combustion reaction. (b) (c) Calculate the molar enthalpy of combustion, ΔH o comb, of propane. Calculate the standard molar enthalpy of formation, ΔH o f, of propane gas. (d) Calculate the entropy change, ΔS o comb, for the reaction and account for the sign ΔS o comb. (2 nd semester) 6.74.Z. The standard enthalpy of combustion of ethane gas, C 2 H 4 (g), is kj/mol at 298 K. Given the following enthalpies of formation, calculate ΔH o f for C 2 H 4 (g). Substance ΔH o f (kj/mol) CO 2 (g) H 2 O (l)

5 1988 B Enthalpy of Absolute Combustion, ΔH o Entropy, S o Substance (kilojoules/mol) (Joules/mol-K) C(s) H 2 (g) C 2 H 5 OH(l) H 2 O(l)?? (a) Write a separate, balanced chemical equation for the combustion of each of the following: C(s), H 2 (g), and C 2 H 5 OH(l). Consider the only products to be CO 2 and/or H 2 O(l). (b) In principle, ethanol can be prepared by the following reaction: 2 C(s) + 2 H 2 (g) + H 2 O(l) C 2 H 5 OH(l) Calculate the standard enthalpy change, ΔH o, for the preparation of ethanol, as shown in the reaction above Z Consider the following reaction: 2H 2 (g) + O 2 (g) 2H 2 O (l) ΔH = -572 kj a) How much heat is evolved for the production of 1.00 mol of H 2 O (l)? b) How much heat is evolved when 186 g of oxygen is reacted with excess hydrogen? c) The total volume of hydrogen gas needed to fill the Hindenburg was 2.0 x 10 8 L at 1.0 atm and 25 o C. How much heat was evolved when the Hindenburg exploded? Assume all the hydrogen reacted.

6 1988 D An experiment is to be performed to determine the standard molar enthalpy of neutralization of a strong acid by a strong base. Standard school laboratory equipment and a supply of standardized 1.00 molar HCl and standardized 1.00 molar NaOH are available. (a) What equipment would be needed? (b) What measurements should be taken? (c) Without performing calculations, describe how the resulting data should be used to obtain the standard molar enthalpy of neutralization. (d) When a class of students performed this experiment, the average of the results was kilojoules per mole. The accepted value for the standard molar enthalpy of neutralization of a strong acid by a strong base is kilojoules per mole. Propose two likely sources of experimental error that could account for the result obtained by the class Z In a coffee-cup calorimeter, 1.60 g of NH 4 NO 3 is mixed with 75.0 g of water at an initial temperature of o C. After dissolution of the salt, the final temperature of the calorimeter is o C. Assuming the solution has a heat capacity of 4.18 J/g o C and assuming no heat loss to the calorimeter, calculate the enthalpy change for the dissolution of NH 4 NO 3 in units of kj/mol.