Download CHM_1220_exam_iv

Department of Chemistry
CHM 1220/1225
Sample Exam IV
1. Consider the reaction: 2 N2O5(g) Æ 4 NO2(g) + O2(g).
Relate the rate expressions in terms of each reactant and product to each other.
2. The following data were determined at 420°C for the gas-phase reaction
PO(g) + Cl2(g) <===> POCl2(g)
Initial Rate
Experiment
[PO]
[Cl2]
M
M • min-1
M
1
0.10
0.10
24
2
0.10
0.20
48
3
0.40
0.40
1536
4
0.20
0.40
384
a.
b.
c.
d.
What is the order in PO?
What is the order in Cl2?
What is the overall order?
What is the value of the rate constant at 420ºC?
e. What is the rate at 420°C if [PO]0 = [Cl2] = 0.30 M?
3. Find the activation energy for a reaction having k = 3.40 x 10–2 at 250 K and k = 6.80 x 10–3 at 214
K.
.
4. What is the half life of a reaction that has [A]0 = 0.15 M and k = 2.7 x 10-6/(M s).
What would the half life be if k = 2.7 x 10-6/s?
5. A proposed mechanism for the reaction: H2 + Br2 –––> 2 HBr is (hν is light energy)
(i)
Br2 + hν –––> 2 Br
rate constant, k1
(ii)
2 Br + 2 H2 –––> 2 HBr + 2 H
rate constant, k2
(iii)
H + Br2 –––> HBr + Br
rate constant, k3
(iv)
H + HBr –––> H2 + Br
rate constant, k4
(v)
Br + Br –––> Br2
rate constant, k5
a. If step (i) is the rate–determining step, what is the rate law expression?
b. Is there a catalyst?
(CIRCLE ONE) YES
NO
If so, what is it?
c. Is there an intermediate?
(CIRCLE ONE) YES
NO
If so, what is it?
6. a. Calculate the concentrations of all substances present in the equilibrium mixture at a given
temperature if 2.35 mol H2 and 2.35 mol I2 are placed in a 10.0 L flask and allowed to come to
equilibrium, at which time 3.76 mol HI is present. The balanced chemical reaction is
H2(g) + I2(g) ' 2 HI(g)
b. What is Kc for the reaction?
c. What is Kc at the same temperature for the following reaction?
2 HI(g) ' H2(g) + I2(g)
7. The following concentrations were found present in a reaction flask: [CS2] = 0.48 M, [H2] = 0.35 M,
[CH4] = 0.42 M, [H2S] = 0.52 M. The relevant reaction follows. Is the reaction at equilibrium? If not,
in which direction is the reaction proceeding? CS2(g) + 4 H2(g) ' CH4(g) + 2 H2S(g); Kc =
0.28.
8. Write the equilibrium constant expression, Kc, for each of the following reactions:
a. 2 Fe(s) + 4 H2O(g) ' Fe2O4(s) + 4 H2(g)
b. 2 NO2(g) + 7 H2(g) ' 2 NH3(g) + 4 H2O(g)
c. 2 CaSO4(s) ' CaO(s) + 2 SO2(g) + O2(g)
9. Calculate the equilibrium concentration of CO in the reaction below, if the initial concentration of
CO2 and H2 is 2.50 M. KC = 0.0667. The reaction is
CO2(g) + H2(g) <===> CO(g) + H2O(g)
10. What is the composition of the equilibrium mixture if you begin with 0.25 mol each of H2 and I2 in a
5.0 L vessel:
H2(g) + I2(g) ' 2 HI(g); Kc = 49.7 at 458°C
11.Given the following equilibrium for the exothermic reaction:
Co(H2O)62+(aq) + 4 Cl–( aq) <==> CoCl42–( aq) + 6 H2O(l)
PINK
BLUE
What would you expect to see in each of the following situations?
a. Adding NaCl? Explain.
b. Lowering the temperature? Explain.
c. Adding water? Explain.
12 Identify each of the following:
a. the conjugate acid of H2PO4—
b. the conjugate base of H2PO4—
c. the conjugate acid of HS–
d. the conjugate base of HS–
13.
a.
b.
c.
d.
Which is the stronger acid:
Which is the stronger acid:
Which is the stronger acid:
Which is the stronger acid:
HOClO3 or HOClF3? Explain.
HOClO3 or HOBrO3? Explain.
HBr or HF? Explain.
H2SO3 or HSO3–? Explain.
14. Given a 2.45 x 10-5M solution of Ba(OH)2
a.
What is the pH of the solution?
b.
What is the pOH of the solution?
c.
What is the [H3O+]?
d.
What is the [OH–]?
e.
Is the solution (CIRCLE ONE)
ACIDIC BASIC NEUTRAL?