Brooklyn College. Chemistry 2. Kinetics and equilibrium.
Name________________________
_____1 2 SO2 + O2 = 2 SO3 + heat. Which would increase the value of the equilibrium
constant? 1) addition of SO3 to the system 2) addition of oxygen to the system 3)an increase in
pressure 4) an increase in temperature 5)a decrease in temperature
_____2. 2 A + B = 2 C + D (all gases)
The initial pressure of gas A is 6.0 atm, and that of B is 3.0 atm. When the reaction has reached
equilibrium, the pressure of gas D is 1.0. Find the equilibrium constant.
1) 8 2) 0.125 3) 1/27 4) 27 5) 0.20
_____3. C(s) + CO2 (g) = 2 CO (g)
Suppose that at a certain temperature the Keq was
-10
1.0x10 for this reaction. If excess carbon is introduced into a vessel with CO2 gas at an
initial pressure of 1.0 atm, find the equilibrium partial pressure of CO .
1) 1.0x10-5 M 2) 1.4x10-5 M 3) 7.0x10-6 M 4) 5.0x10-6M 5) 1.5x105 M
_____4. 2 NO + O2 = 2 NO2 + heat (all gases)
If at equilibrium the pressure of all three gases in this system is 2.0 atm, what is the
equilibrium constant for the reaction? 1)1.0
2) 2.0 3) 0.50 4) 36 5) 6.73
_____5. 2 A + B = 2 C (all gases). When the concentration of B in this reaction is doubled, all
other factors being held constant, it is found that the rate of the reaction remains unchanged.
The most probable explanation for this observation is that
1) the rate order with respect to substance B is 1
2) Substance B is not involved in any of the steps in the mechanism of the reaction.
3) substance B is not involved in the rate determining step of the mechanism, but is
involved in subsequent steps.
4) Substance B is probably a catalyst, and thus its effect on the rate does not depend
upon its concentration.
5) The reactant with the smallest coefficient in the balanced equation generally has
little or no effect on the rate of the reaction.
_____6. A reaction 2A + 2 B ➞ A2B2 proceeds by the following steps:
1) A + B ➞ AB (fast) 2) AB + A ➞ A2B (slow)
3) A2B + B ➞ A2B2 (fast)
The rate expression would be: Rate =
1) k[A][B]
2) k[A]2[B]2
3) k[A]2[B]
4) k[A][B]2
5) k[A]2
_____7 The reaction 2 NO(g) + O2(g) ➞ 2 NO2(g) is found to obey the rate law:
Rate = k[NO]2[O2]. What would be the effect on the rate of this reaction, of tripling the volume
of the reaction vessel? 1)rate would triple 2) rate would be 1/3 of original 3)rate would be
1/9 of original 4) rate would be 1/27 of original 5) rate would be 1/81 of original
Questions 8 to 11 are based on the following data for A + B + C ➞ D
Initial concentrations.
[A]
2M
2M
1M
1M
[B]
2M
1M
1M
2M
Initial rate of appearance of D
[C]
(in M/sec)
8x10 -3
2x10 -3
2x10 -3
4x10 -3
2M
2M
2M
1M
_____8. The total reaction order is 1)first 2)second 3)third 4)fourth 5)fifth
_____9. The rate expression is rate = 1) k[A][B][C] 2) k[B]2[C] 3) k[A][B]2[C]
4) k[B][C]2 5) k[A][B]2[C]2
_____10. The value of the rate constant is 1) 1x10-3 2) 6.4x10-2 3) 1x103
2x10-3
4) 1.6x10-4
5)
_____11. What would the initial rate be, in M/sec, if the initial concentrations of the three
components were all 4.0 M? 1) 6.4x10-2 2) 3.2x10-2 3) 0.016 4) 0.13
5) 0.0010
_____12.What is the rate constant for a first order reaction whose half life is 1.38 seconds?
1)0.50 2) 2.0 3) 2.76 4) 0.69 5) 1.38 (sec-1)
______13. If the value of the equilibrium constant for the reaction 4 C (g) = A (g) + 2 B (liq.)
is 0.123 atm-3, the value of the equilibrium constant for the reaction
A (g) + 2 B (liq)= 4 C (g) is 1) 0.123 2) 6.47 3) 8.13 4) (1/.123)4 5) (1/.123)3
______14. What is the [OH–] in a solution with a pH of 3.00 ?
2) 3.0 x 10–3 M
3) 1.0 x 10–11 M
4) 11.00 M
1) 1.0 x 10–3 M
5) 3.00 M
______15. Which of the following is a Lewis acid, but NOT a Bronsted acid?
1) HCl
2) NH4+
3) Fe3+
4) O2–
______16.
The conjugate base of H2PO4– is
4) OH–
5) H3O+
For the reaction 2 PCl3(g)
+ O2(g)
⇄
1) H3PO4
2) HPO42–
3) PO43–
2 POCl3(g) , ΔH̊ = –508 kJ.
Predict how the equilibrium quantity of O2 would be affected, (increased, decreased, or
unchanged) by each of the following adjustments to the system:
_____________17. The temperature is increased
_____________18.
The volume of the system is decreased
_____________19.
Additional PCl3 is added to the system.
For the reaction
N2 + O2 ⇄ 2 NO (all gases) ΔH̊ is + 181 kJ.
Predict how the equilibrium quantity of O2 would be affected by each of the following adjustments
to the system:
_______________20. Nitrogen is removed from the system
_______________21.
The temperature is decreased
_______________22.
The volume of the system is increased
________23. A 0.200 molar NaOH solution is titrated with a 0.200 molar HCl solution. What
is the molarity of Cl– ion in the solution at the equivalence point?
1) 0.100 M
2) 0.200 M
3) 0.300 M
4) 0.400 M
_____________24. Given that the Kb of CN– ion is 2.4 x 10–5 , find the Ka of HCN.
_________25. In qualitative analysis, Pb2+ , Ag+, and Hg22+ are initially precipitated as
1) nitrates 2) chlorides
3) sulfides
4) chromates
_________26. AgCl is dissolved through the addition of concentrated NH3 solution:
AgCl(s) + 2NH3(aq) ➞ Ag(NH3)2+(aq) + Cl–(aq)
In this reaction, the NH3 is acting as a 1)Bronsted acid
3) Lewis acid
4) Lewis base
2) Bronsted base
Essay questions.
I. Given: The Ka of HC2H3O2 is 1.8 x 10–5 , and the Kb of CH3NH2 is 4.4 x 10–4 .
A. Find the pH of each of the following solutions: (2 pts each)
1. 0.0250 M HCl ___________
3. 0.30 M NaOH __________
2. 0.40 M
4. 0.50 M
HC2H3O2 _________
CH3NH3+ __________
B. Write the balanced equation for the ionization of CH3NH2 in water, and label all acids
and bases according to Bronsted-Lowry theory. (4 pts)
II.
For a certain acid, HA, the pH of a 0.200 molar solution is 3.20.
A. Find the % ionization of the acid when it is 0.200 molar
B. Find the Ka of the acid, HA.
(10)
C.
Find the pH, and the % ionization of a 0.500 molar solution of HA.
( If you are unable to complete part B, above, use a Ka of 2.0 x 10–4 to complete part
C. )
III. For a hypothetical chemical reaction that has the stoichiometry 2 X + Y ➞ Z
the following initial rate data were obtained. (All measurements were made at the same
temperature.)
Initial rate of
formation of Z. M sec-1
7.0x10-4
1.4x10-3
2.8x10-3
4.2x10-3
Initial [X]
M
0.20
0.40
0.40
0.60
a) give the rate law for the data above.
Initial [Y]
M
0.10
0.20
0.40
0.60
(3)
b) Calculate the specific rate constant for this reaction, and specify its units (3)
c)When the initial [X] is 0.20 M, and [Y] is 0.10 M, what is the initial rate of disappearance of X?
(2)
d) (extra credit, 4 pts) How long must the reaction proceed to produce a conc. of Z equal to 0.20M
if the initial reaction concentrations are [X]=0.80 M, [Y]=0.60 M and [Z] = 0 M ?
e) Select from the mechanisms below the one most consistent with the
observed data, and explain your choice. M and N are intermediates. (3)
1) X + Y ➞ M (slow) 2) X + X ➞ M (fast) 3) Y ➞ M (slow)
X + M➞ Z (fast)
Y + M ➞ Z (slow)
M + X ➞N (fast)
N + X ➞ Z (fast)
IV. A buffer solution contains 0.13 mol of sodium acetate and 0.10 mole of acetic acid in
B. What is the pH of this buffer after the addition of 0.040 mol of KOH? (3)
C. What is the pH of the original buffer after the addition of 0.080 mol of HNO3? (3)
D. What is the pH of the original buffer after the addition of 500. mL of water? (2)
500.mL.
A.
V.
40.0 mL of 0.20 molar HCl is titrated with 0.40 molar NaOH.
A. What is the initial pH of the HCl solution?
VI.
(2)
B.
What is the total volume of the solution at the equivalence point? (2)
C.
What is the pH after the addition of 15. mL of the 0.40 M NaOH? (3)
D.
What is the pH after the addition of 20. mL of the NaOH ? (2)
40.0 mL of 0.20 molar lactic acid, (HC3H5O3, Ka = 1.4 x 10–4) is titrated with 0.20 M
NaOH.
A. What is the initial pH of the lactic acid solution? (3)
B.
What is the pH after the addition of 20.0 mL the base? (3)
C.
What is the pH after the addition of 40.0 mL of the base? (3)
D. What is the pH after the addition of 50.0 mL of the base?
(3)