EXTRA UNIT 9 PROBLEMS FOR THE WEB
PAGE:Kinetics and Thermodynamics.
1. Find delta G for the following reactions and predict spontaneity at standard conditions.
(delta Gf0 : Mg3N2 = -422 kJ/mol; HNO3(aq) = -110.5 kJ/mol; Cu(NO3)2 = -156.06
kJ/mol; H2O(l) = -236.81 kJ/mol; NO(g) = +86.71 kJ/mol)
a) 3Mg(s) + N2(g) ---> Mg3N2(s)
b) 3Cu(s) + 8HNO3(aq) ---> 3Cu(NO3)2(aq) + 4H2O(l) + 2NO(g)
2. Find delta H for the following reactions. (delta H0f : NO(g) = +90.37 kJ/mol; NO2(g) =
+33.84 kJ/mol; HNO3(aq) = -206.6 kJ/mol; NH3(g) = -46.19 kJ/mol; H2O(l) = -285.85
kJ/mol; Zn(NO3)2(aq) =-568.2 kJ/mol)
a) 2NO(g) + O2(g) ---> 2NO2(g)
b) 4Zn(s) + 9HNO3(aq) ---> 4Zn(NO3)2(aq) + NH3(g) + 3H2O(l)
3. Find delta S for the following reaction. S0 HBr = 198.49 J/K; S0 O2 = 205.0 J/K; S0
H2O (l) = 69.96 J/K; S0 Br2 (l) = 152.3 J/K.
4HBr(g) + O2(g) ---> 2H2O(l) + 2Br2(l)
4. Predict the spontaneity of the following reactions at 298 K using delta G = delta H - T
delta S.
a) I2(s) + Cl2(g) ---> 2ICl(l) (delta H = -47.8 kJ, delta S = -16.45 J/K)
b) Na2O(s) + SiO2(s) ---> Na2SiO3(s) (delta H = -192 kJ, delta S = -0.837 J/K)
5. Calculate the enthalpy of formation of carbon dioxide from its elements.
C(g) + 2O(g) ---> CO2(g)
Use the following data:
2O(g) ---> O2(g) ; delta H = -250 kJ
C(s) ---> C(g) ; delta H = +729 kJ
CO2(g) ---> C(s) + O2(g) ; delta H = -390 kJ
6. If delta H = + 66 kJ for the reaction Ca(OH)2(s) ---> CaO(s) + H2O(l), what is the heat
of formation for CaO(s)? Delta H0f Ca(OH)2 = -986.2 kJ/mol ; Delta H0f H2O (l) = 285.85 kJ/mol
7. Calculate the heat of formation for 1 mole of octane gas, C8H18, from the following
reaction.
C8H18(l) + 25/2 O2(g) ---> 8CO2(g) + 9H2O(g) . Heat of reaction = -5445 kJ; delta
H0f CO2 (g) = -393.3 kJ/mol; delta H0f H2O (g) = -241.6 kJ/mol
8. Calculate the enthalpy of reaction for the equation listed below:
CuCl2(s) + Cu(s) ---> 2CuCl(s)
Use the following data:
Cu(s) + Cl2(g) ---> CuCl2(s) ; delta H = -206 kJ
2Cu(s) + Cl2(g) ---> 2CuCl(s) ; delta H = -136 kJ
Answers: 1a. -422 kJ; spontaneous, 1b. -358 kJ; spontaneous, 2a. -114 kJ, 2b.
-1317 kJ, 3. -555 J/K, 4a. -42.9 kJ; spontaneous, 4b. -192 kJ; spontaneous, 5. 588 kJ, 6. -634 kJ/mol, 7. -125 kJ/mol, 8. +70 kJ.
The following is an example of an Honors test for Unit 9: Kinetics
and Thermodynamics.
Multiple Choice.
1. Changes in reaction rate are explained using (a) collision theory (b) quantum theory (c)
uncertainty theory (d) probability theory.
2. Rates of many reactions are approximately doubled when the temperature (a) is
doubled (b) increases by 10oC (c) increases by 100oC (d) decreases by 10oC.
3. The catalysts in many of the biochemical changes in the human body are (a)
radioactive isotopes (b) suppressants (c) narcotics (d) enzymes.
4. The series of steps in a chemical reaction is called the reaction (a) breakdown (b) order
(c) sequence (d) mechanism.
5. Each of the several steps in a chemical reaction may occur at a different rate. The
slowest step is called the (a) rate-determining step (b) catalyzed step (c) intermediate step
(d) activated step.
6. Unstable, intermediate products that form when particles of the reactants collide with
sufficient energy are called (a) activated complexes (b) catalytic substances (c) threshold
substances (d) reversible products.
7. In the graph for the reaction X + Y ----> W, the activation energy is represented by the
letter (a) A (b) B (c) C (d) D. (Get the diagram from Ms. Fed).
8. A catalyst enables a reaction to speed up by providing a new mechanism with a (a)
lower activation energy (b) higher activation energy (c) lower heat of reaction (d) higher
heat of reaction.
9. In which would you have the fastest reaction at room temperature? (a) C6H12O6(s) +
O2(g) ----> (b) Zn(s) + S8(s) ----> (c) Cl-(aq) + Ag+(aq) ----> (d) KMnO4(s) + Br-(aq) --->
10. The difference between the heat content of the products and the heat content of the
reactants is (a) entropy of reaction (b) heat of reaction (c) free energy (d) activation
energy.
11. Given the reaction: N2(g) + O2(g) + 43.2 kcal ----> 2NO(g) , what is the heat of
formation of nitrogen(II) oxide in kcal/mol? (a) -43.2 (b) -21.6 (c) 21.6 (d) 43.2.
12. In order for an endothermic reaction to occur spontaneously, the entropy must (a)
decrease (b) increase (c) remain the same.
13. In the reaction: A(s) + B(s) ----> C(g) + D(g) + heat, the entropy of the system (a)
increases and the reaction is exothermic (b) increases and the reaction is endothermic (c)
decreases and the reaction is exothermic (d) decreases and the reaction is endothermic.
14. The following list represents compounds and their standard enthalpies of formation,
in kJ/mol. Choose the one that is the most thermodynamically stable. (a) N2O(g) , +82.1
(b) H2O(g) , -242 (c) CO2(g) , -393.5 (d) C2H4(g) , +52.8.
15. Which of the following has an arbitrarily set value of zero? (a) the entropy of a 1
molar solution (b) the free energy of a spontaneous reaction (c) the enthalpy of free
elements (d) the internal energy of a crystal.
16. Which of the following is the definition of thermodynamic equilibrium? (a) TdeltaS =
0 (b) deltaH < 0 (c) PdeltaV > 0 (d) deltaG = 0.
Problems:
17. Given the following potential energy diagrams, (get these from Ms. Fed), which
diagram accurately illustrates each situation listed below?
(i) an explosive reaction (ii) a very slow reaction (iii) a reaction with the smallest positive
delta H value (iv) an exothermic reaction with the smallest delta H value.
18. Given the following mechanism:
(1) FeBr3 + Br2 ----> Br+ + FeBr4(2) C6H6 + Br+ ----> C6H5Br + H+
(3) FeBr4- + H+ ----> HBr + FeBr3
(a) Write the net ionic equation for the overall reaction (b) what substance is the activated
complex? (c) what substance is the catalyst?
19. The standard heat of combustion of liquid ethanol is -327 kcal/mol, and that of acetic
acid is -209 kcal/mol. The equations are:
C2H5OH(l) + 3 O2(g) ----> 2CO2(g) + 3H2O(l) ; delta H = -327 kcal
CH3COOH(aq) + 2 O2(g) ----> 2CO2(g) + 2H2O(l) ; delta H= -209 kcal
What is the heat of reaction for the oxidation of ethanol to acetic acid? (Use the longform of Hess' Law)
C2H5OH(l) + O2(g) ----> CH3COOH(aq) + H2O(l)
20. (a) Given that delta Gof for C6H12O6(s) = -907.9 kJ/mol; delta Gof for CO2(g) = -394.6
kJ/mol; and delta Gof for H2O(l) = -237.2 kJ/mol at 298 K, calculate delta Go for the
oxidation of glucose:
C6H12O6(s) + 6 O2(g) = 6CO2(g) + 6H2O(l)
(b) Is the oxidation of glucose spontaneous at standard conditions? Explain your answer.
Answers: 1 a, 2 b, 3 d, 4 d, 5 a, 6 a, 7 a, 8 a, 9 c, 10 b, 11 c, 12 b, 13 a, 14 c, 15 c, 16 d,
17(a) B, (b) C (c) A (d) D, 18(a) C6H6 + Br2 ---> C6H5Br + HBr (b) FeBr4+ (c) FeBr3 ,
19: reverse reaction #2 and add the two equations; delta H = -118 kcal, 20: delta G =
-2882.9 kJ