Name ______
EXAM #1 CHEMICAL KINETICS AND CHEMICAL EQUILIBRIUM
VERSION A
Multiple choice questions 1 point each, long questions 10 points each. There are 20 multiple choice and 2 long questions making 40 points total, there is additional extra credit worth 4 points
Assume that R = 8.314Jmol-1K-1 except in problems where P is in atmospheres, then use R = 0.08206 L atm/(mol K)
Answer multiple choice on a scantron
1. For the reaction which of the following below is a correct expression for the rate?
2. Assuming that the reaction is first-order in H2 and first-order in I2, which of the following statements is true
3. The reaction is first-order in N2O5. The rate constant is found to be 0.053/s at a certain temperature. If initially the concentration of N2O5 is 1M and the concentrations of NO3 and NO2 are zero. What would you predict the concentration of the N2O5 to be after 3 seconds?
4. What is the integrated rate law for the concentration of a reactant A when the reaction is second order in A for the reaction A products?
5. A plot of ln(Rate Constant) versus 1/Temperature for the following first-order reaction:
gives a straight line graph of slope = -30189K and an intercept of 29.967. Which of the following answers is correct?
(a) Ea = 30.189 kJ/mol and A=29.967 s-1: (b) Ea = 3631 J/mol and A = 1.03x10-13 s-1
(c) Ea = 3.631 kJ/mol and A = 1.03x1013 s-1 (d) Ea = 251 kJ/mol and A = 1.03x10-13 s-1
(e) Ea = 251 kJ/mol and A = 1.03x1013 s-1
6. Consider the following 3-step mechanism for a reaction
What is the predicted rate law?
7. What is the overall order for the above reaction?
(a) 3/2;
(b) 1;
(c) 2;
(d) 0;
(e) none of these?
8. In the reaction in question (6) what would happen to the rate of reaction if I double the concentration of Cl2 and double the concentration of CHCl3?
(a) rate remains the same:
(b) rate quadruples:
(c) rate increases by a factor of 2.83:
(d) the rate doubles:
(e) none of these?
9. Consider the two 1-step elementary reactions, (i) H + I HI and (ii) NOCl + NOCl 2NO + Cl2. Let us assume that both reactions have the same activation barrier height, and the same collision frequency factor z. Which reaction would have the fastest rate?
(a) reaction (i)
(b) reaction (ii)
(c) they would have the same rate
10. Consider the reaction , where the reaction is found to be first order in A and 0 order in B. What would happen to the rate of reaction if I double the concentration of A and double the concentration of B?
(a) rate remains the same: (b) rate quadruples: (c) rate increases by a factor of 2.83: (d) the rate doubles: (e) none of these?
Chemical Equilibrium
11. For the general reaction what is the equilibrium constant Kc?
12. What is the equilibrium constant for the following reaction,
13. For which of the following reactions will Kp = Kc?
14. Consider the following reaction:
A reaction mixture at 780oC initially contains [CO]=0.5M and [H2]=1M. At equilibrium the CO concentration is found to be 0.15M. What is the equilibrium constant for the reaction?
(a) 26 (b) 0.385 (c) 3.59 (d) 0.278 (e) 6.67
15. Consider the following reaction . A reaction mixture contains , is the reaction mixture at equilibrium and if not in which direction will it proceed?
(a) yes, will not change
(b) no, will move toward the right
(c) no, will move toward the left.
16. Consider the following reaction of nitrogen and hydrogen to make ammonia occurring inside a piston, equilibrium is established and the concentrations of the reactants and product measured. You then push the piston down to increase the pressure of the gases and decrease the volume, what happens to the equilibrium?
(a) the equilibrium shifts right toward product
(b) the equilibrium shifts left toward reactants
(c) there is no change in the concentration of reactants or products
17. Consider the reaction
the reaction is known to be exothermic. The equilibrium concentrations of the H2, and I2 and HI are measured at 1000K. The temperature of the reaction vessel is changed to 800K. What happens to the reaction equilibrium, does it
(a) shift left
(b) shift right
(c) remain unaffected?
18. Consider the following observations about the reaction
Is this reaction
(a) exothermic, (b) endothermic, (c) neither?
The reaction 2 SO2(g) + O2(g) 2 SO3(g) with ΔH° = -198 kJ at equilibrium. How will each of the following changes affect the equilibrium concentrations of each gas once equilibrium is re-established?
19. Adding more O2 to the container
(a) Equilibrium shifts left
(b) Equilibrium shifts right
(c) Equilibrium remains unchanged
20. Cooling the container
(a) Equilibrium shifts left
(b) Equilibrium shifts right
(c) Equilibrium remains unchanged
LONG QUESTIONS (10 POINTS EACH) (attach sheets showing working)
21. For the following two-step reaction mechanism,
(a) write out the overall reaction (2 points)
(b) what is the reactive intermediate? (1 points)
(c) is the first step or the second step rate determining? (1 point)
(c) What is the rate law for this reaction in terms of [O3] and [O2] (6 points)
22. Consider again the reaction . At 25oC the mixture initially contains .
(a) Find the equilibrium partial pressures of I2, Cl2 and ICl at this temperature. (6 points)
(b) what will Kc be at this temperature? (4 point)
Extra-Credit (worth 4 points)
During the kinetic study of the reaction, 2A + B → C + D, following results were obtained:
Run / [A]/mol L–1 / [B]/mol L–1 / Initial rate of formation of D in mol L–1s–1I / 0.1 / 0.1 / 6.0 × 10–3
II / 0.3 / 0.2 / 7.2 × 10–2
III / 0.3 / 0.4 / 2.88 × 10–1
IV / 0.4 / 0.1 / 2.40 × 10–2
If the general rate law is written
Rate = k [A]x.[B]y
Find x, y and k (show all working for full credit)
x = ___
y = ___
k = ______(don’t forget the units)
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