Homework
Chapter 17


17.1

1. Determine the specific heat of a material if a 35 g sample absorbed 48 J as it was heated from 293 K to 313 K. ( 0.069 J/g.K ) soln

2. If 980 kJ of energy are added to 6.2 L of water at 291 K, what will the final temperature of the water be? (329 K) soln

3. How much heat energy is needed to raise the temperature of a 55 g sample of aluminum from 22.4 degrees Celsius to 94.6 degrees Celsius. See text for specific heat of aluminum. (3.6 x 103 J) soln

4. 3.5 kJ of heat are added to a 28.2 g sample of iron at 20 degrblackees Celsius. What is the final temperature of theiron in Kelvin. See text for specific heat of iron. (569 K) soln




17.2

1. Calculate the heat of reaction for the combustion of methane gas, CH4, to form CO2(g) + H2O(l). Write all equations involved.

2. Carbon occurs in two distinct forms. It can be the soft, black material found in pencils and lock lubricants, called graphite, or it can be the hard, brilliant gem we know as diamond. Calculate delta H0 for the conversion of graphite to diamond which is the following reaction:

C graphite (s) ---> C diamond (s)

You should use the following reactions to solve this problem:

C graphite (s) + O2(g) ---> CO2(g) delta H0c = -394 kJ/mol

C diamond (s) + O2(g) ---> CO2(g) delta H0c = -396 kJ/mol

3. How does the energy of the products of a reaciton system compare with the energy of the reactatns when the reaction is a) endothermic; b) exothermic.

4. a) Distinguish between heats of reaction, formation, and combustion.

b) On what basis are heats of formation and combustion defined?

5. What factors affect the value of delta H is a reaction system?


17.3

1. Calculate the heat of formation of butane, C4H10, using the balanced chemical equation and information in Appendis Table A-5 of your text and Table A-14 of your text. Write out the solution according to Hess' Law

Final equation: 4 C + 5H2 ----> C4H10

Use equations:

C4H10 + 13/2 O2 ----> 4 CO2 + 5 H2O deltal Hc = -2877.6 kJ

C + O2 ----> CO2 delta Hf = -393.5 kJ

H2 + 1/2 O2 ---> H2O delta Hf = -241.8 kJ

2. Calculate the heat of combustion of 1 mol of nitrogen, N2, to form NO2 using the balanced chemical equation and Appendis Table A-14. (+66.36 kJ/mol)

3. Calculate the heat of formation for sulfur dioxide, SO2, from its elements, sulfur and oxygen. Use the balanced chemical equation and the following information:

S(s) + 3/2 O2(g) -----> SO3(g) delta Hoc = -395.2 kJ/mol

2 SO2(g) + O2(g) -----> 2 SO3(g) delta Ho = -198.2 kJ/mol



17.4

1. What is meant by enthalphy change?

2. Describe the relationship between a compound's stability and its heat of formation.

3. For the vaporization reaction Br2(l) ---> Br2(g), delta H0 = 31.0 kJ/mol and delta S0 = 93.0 kJ / (mol.K). At what

temperature will this process be spontaneous? (above 333 K)

4. What kind of enthalpy change favors a spontaneous reaction?

5. Define entropy, and how does it relate to spontaneity of reactions?

6. List several changes that result in an entropy increase.

7. Define free energy and give the equation used to find it.

8. Explain the relationship between free energy change and spontaneity of reactions.

9. In the reaction in Sample Problem 17-4, why does the entropy increase?

10. How should increasing temerpature affect the value of delta G for the reaction in Sample Problem 17-4?

11. Predict the sign of delta S0 for each of the following reactions:

a) CaCO3(s) ---> CaO(s) + CO2(g)

b) 2 SO2(g) + O2(g) ---> 2 SO3(g)

17.5

1. What is meant by reaction mechanism?

2. What factors determine whether a molecular collision produces a reaction?

3.What is activation energy?

4. What is an activated complex?

5. How is activation energy related to the energy of reaction?


17.6
1. The rate of a reaction involving L, M, and N is found to double if the concentration of L is doubled if the concentration of L is doubled, to increase eightfold if the concentration of M is doubled and to double if the concentration of N is doubled. Write the rate law for this reaction.

2. At temperatures below 498 K, the following reaction takes place:

NO2(g) + CO(g) -----> CO2(g) + NO(g)

Doubling the concentration of NO2 quadruples the rate of CO2 being formed if the CO concentration is held constant. However, doubling the concentration of CO has no effect on the rate of CO2 formation. Write a rate-law expression for this reaction.

3. What is studied in the branch of chemistry that is known as chemical kinetics?

4. List the five important factors that influence the rate of chemical reactions.

5. a) What is a catalyst?
b) Explain the effect of a catalyst on the rate of chemical reactions.
c) W=How does a catalyst influence the activation energy required by a particular reaction?

6. a) What is meany by a rate law for a chemical reaction?
b) Explain the conditions under which a rate law can be written from a chemical equation.
c) When can a rate law not be written from a single step?