Ch 223 Practice Exam #1 PART I: Multiple Choice

Ch 223
Practice Exam #1
PART I: Multiple Choice - Each question is worth 3 points and there is only one BEST
answer.
1. For the hypothetical reaction A + 3B  2C, the rate of appearance of C given by ([C]/t)
may also be expressed as
A.
[C] [A]

t
t
B.
[C]  [B]

t
2/3 t
C.
[C] 2/3 [B]

t
t
D.
[C] 1/2 [A]

t
t
2. Nitric oxide gas (NO) reacts with chlorine gas according to the equation NO + ½ Cl2 
NOCl. The following initial rates of reaction have been measured for the given reagent
concentrations.
Expt. #
1
2
3
Rate (M/hr)
1.19
4.79
9.59
NO (M)
0.50
1.00
1.00
Cl2(M)
0.50
0.50
1.0
Which of the following is the rate law (rate equation) for this reaction?
(a) rate = k[NO]
(d) rate = k[NO]2[Cl2]
(b) rate = k[NO][Cl2]3
(e) rate = k[NO]2[Cl2]2
(c) rate = k[NO][Cl2]
3. For the reaction X + Y  Z, the reaction rate is found to depend only upon the concentration
of X. A plot of 1/X verses time gives a straight line. What is the rate law for this reaction?
(a) rate = k [X]
(b) rate = k [X]2
(c) rate = k [X][Y]
(d) rate = k [X]2[Y]
Use the following information to answer questions 5 and 6:
4. For the chemical reaction system described by the diagram above, which statement is true?
(a) The forward reaction is endothermic.
(b) The activation energy for the forward reaction is greater than the activation energy for the
reverse reaction.
(c) At equilibrium, the activation energy for the forward reaction is equal to the activation
energy for the reverse reaction.
(d) The activation energy for the reverse reaction is greater than the activation energy for the
forward reaction.
(e) The reverse reaction is exothermic.
5. If the Ea for the forward reaction is 25 kJ/mol, and the enthalpy of reaction is -95 kJ/mol,
what is Ea for the reverse reaction?
(a) 120 kJ/mol
(b) 70 kJ/mol (c) 95 kJ/mol (d) 25 kJ/mol (e) -70 kJ/mol
6. Consider the two gas phase equilibria
SO 2(g) + 1/2O 2(g)
SO 3(g)
2SO3(g)
2SO 2(g) + O2(g)
K1
K2
The values of the equilibrium constants K1 and K2 are related by
(a) K2 = (K1)2
(a) K2 = 1/K2
(b) (K2)2 = K1
(c) K2 = 1/(K1)2
(e) none of the above
7. Calculate Kp for the reaction below at 400C if Kc at 400C for this reaction is 2.1  10–2.
2 NOCl(g)
(a) 2.1  10–2
(b) 1.7  10–3
2 NO(g) + Cl2(g)
(c) 0.70
(d) 1.2
(e) 3.8  10–4
PART III: Calculations And Short Answer (35 pts) - You must show all work and follow
significant figure conventions to receive full credit.
1. For the following reaction the initial concentrations are [H2]o = 0.100 M, [I2]o = 0.100 M, and
[HI]o = 1.00 M:
H2(g) + I2(g) = 2HI(g)
(a) (3 pts) If Kc = 54.3, then predict which direction the equilibrium will shift.
2. (12 pts) At 25 oC, the rate constant for the first-order decomposition of a pesticide solution is
6.40 x 10–3 min–1. If the starting concentration of pesticide is 0.0314 M, what concentration
will remain after 62.0 min at 25 oC?
3. The following questions refer to this plot:
-4
-5
-6
-7
-8
-9
-10
-11
-12
0.0029
0.003
0.0031
0.0032
0.0033
0.0034
(a) (2 pts) If the plot is data made to fit the linearized Arrhenius equation, then the xaxis is
_________ and the yaxis is __________.
(b) (10 pts) What is the activation energy? You must show work.