Chemistry 223
Worksheet 1
Summer 2002
June 25, 2002
Dr. Nafshun
(Same as CH 222 Worksheet 10)
1.
Write the equilibrium law expression for the reaction 2NO(g)  N2(g) + O2(g)
Kc = [N2][O2]/[NO]2
2.
Write the equilibrium law expression for the reaction CO(g) + Br2(g)  COBr2(g)
Kc = [COBr2]/[CO][Br2]
3.
Write the equilibrium law expression for the reaction H2(g) + I2(g)  2HI(g)
Kc = [HI]2/[H2][I2]
4.
The following reaction was allowed to come to equilibrium at 430 K.
SO2(g) + NO2(g)  NO(g) + SO3(g)
The equilibrium concentrations were analyzed and found to be:
[SO2] = 1.31 M
[NO2] = 1.42 M
[NO] = 9.67 M
[SO3] = 12.2 M
What is the value of Kc?
Kc = [NO][SO3]/[SO2][NO2]
Kc = [9.67][12.2]/[1.31][1.42]
Kc = 63.4
5.
The following reaction was allowed to come to equilibrium at 419 K.
2NO(g) + O2(g)  2NO2(g)
The equilibrium concentrations were analyzed and found to be:
[O2] = 0.768 M
[NO2] = 0.865 M
[NO] = 0.871 M.
What is the value of Kc?
Kc = [NO2]2/[NO]2[O2]
Kc = [0.865]2/[0.871]2[0.768]
Kc = 1.28
6.
The equilibrium constant for the reaction below was Kc = 2.72E-6
2NH3(g)  3H2(g) + N2(g)
What is the value of Kc for the REVERSE reaction given below?
3H2(g) + N2(g)  2NH3(g)
Kc for the bottom reaction is the inverse of the Kc for the top reaction (the reactions are
inverses of each other).
Kc = 1 / 2.72E-6 = 3.68E5
7.
For the reaction equation below, Kc = 24.9
2NO(g) + Br2(g)  2NOBr(g)
Which predominate at equilibrium?
(A)
PRODUCTS GREATLY predominate.
(B)
PRODUCTS moderately predominate. (Kc is a bit greater than 1 implying
products predominate—but not greatly).
(C)
REACTANTS moderately predominate.
(D)
REACTANTS GREATLY predominate.
(E)
There are EQUAL amounts of PRODUCTS and REACTANTS.
8.
For the reaction equation below, Kc = 5.05E-13
2HBr(g)  H2(g) + Br2(g)
Which predominate at equilibrium?
(A)
PRODUCTS GREATLY predominate.
(B)
PRODUCTS moderately predominate.
(C)
REACTANTS moderately predominate.
(D)
REACTANTS GREATLY predominate. (Kc is a lot less than 1 implying
reactants predominate—and greatly).
(E)
There are EQUAL amounts of PRODUCTS and REACTANTS.
9.
For the reaction equation below, Kc = 7.35E-24
2SO3(g)  2SO2(g) + O2(g)
Which predominates at equilibrium?
(A)
PRODUCTS GREATLY predominate.
(B)
PRODUCTS moderately predominate.
(C)
REACTANTS moderately predominate.
(D)
REACTANTS GREATLY predominate. (Kc is a lot less than 1 implying
reactants predominate—and greatly).
(E)
There are EQUAL amounts of PRODUCTS and REACTANTS.
10.
For the following reaction
PCl3(g) + Cl2(g)  PCl5(g)
The partial pressures at equilibrium were:
P(PCl3) = 0.821 atm
P(Cl2) = 0.821 atm
What is the value of Kp?
Kp = PPCl5/PPCl3 PCl2
Kp = (73.5)/(0.821)(0.821)
Kp = 109
P(PCl5) = 73.5 atm
11.
For the following reaction
2 NO(g) + Cl2(g)  2 NOCl(g)
The partial pressures at equilibrium were:
P(NO) = 0.630 atm
P(Cl2) = 0.315 atm
What is the value of Kp?
P(NOCl) = 1.41 atm
Kp = [PNOCl]2/[PNO]2 PCl2
Kp = (1.41)2/(0.630)2(0.315)
Kp = 15.9
12.
For the following reaction, the value of Kc = 8.16.
2 NO2(g)  N2O4(g)
What is the value for Kp at 449 K?
Kp = Kc(RT)Δmoles of gas; where R = 0.0821 L·atm/mol·K
Kp = (8.16) (0.0821 L·atm/mol·K x 449 K)-1
Kp = (8.16)(0.0271) = 0.221
13.
Kc for the cis- and trans- isomers of 2-butene is given in Table 14.1:
cis-2-butene  trans-2-butene
Kc = 3.2
Discuss the implications.
Dynamic equalibrium and the trans- isomer is more favorable (possibly due to steric
considerations).
14.
How does a catalyst effect equilibrium? It does not shift equilibrium. It allows the
system to reach equilibrium is less time.
15.
What is meant by dynamic equilibrium? Not static—the concentrations of the
components are constant but the reactants are continually changing into products and the
products are continually changing into reactants at the same rate!
16.
Which of the following reactions would have the same value for Kp and Kc?
2 NO(g)  N2(g) + O2(g) Same moles of gas "before and after."
2 NO + Br2(g)  2 NOBr(g)
2 SO2(g) + O2(g)  2 SO3(g)
PCl3(g) + Cl2(g)  PCl5(g)
2 NH3(g)  N2(g) + 3 H2(g)
17.
Write the equilibrium law expression for the reaction (do pure phases appear in the
expression?) 2N2H6CO2(s)  2NH3(g) + CO2(g)
Kc = [NH3(g)]2[CO2(g)]
18.
Write the equilibrium law expression for the reaction
2PbS(s) + 3O2(g)  2PbO(s) + 2SO2(g)
Kc = [SO2(g)]2[O2(g)]3
19.
Find the value of the equilibrium constant, Kc, for the reaction:
2NH3(g) + CO2(g)  2N2H6CO2(s)
Initially, 3.0 mol of N2H6CO2 was placed in a 1.0-L flask at 437 K.
At equilibrium… [NH3] = 1.0 M and [CO2] = 0.50 M
Kc = 1/[NH3(g)]2[CO2(g)]
Kc = 1/[1.0]2[0.50] = 2.0
20.
The following reaction had Kc = 85.0
SO2(g)+ NO2(g)  NO(g)+ SO3(g)
At equil.: [SO2] = 0.0112 M, [NO] = 0.869 M, and [NO2] = 0.277 M
What is the concentration of SO3 in mol/L?
[______]
Kc = [NO(g)][SO3(g)]/[SO2(g)][NO2(g)]
85.0 = [0.869][SO3(g)]/[0.0112][0.277]
[SO3(g)] = 0.303 M
21.
The equilibrium constant for the following reaction at 825C is 49.5.
SO2(g)+ NO2(g)  NO(g)+ SO3(g)
To start the reaction, 2.0 mol of both SO2 and NO2 are placed in a 2.0 L reactor. What is
the concentration of NO, after the reaction came to equilibrium at 825C?
22.
Which of the following chemical equilibria could be solved by the same simplification
we used in the last problem, that is, by taking the square root of both sides of the
equilibrium constant expression?
2NH3(g)  N2(g) + 3H2(g)
2NO2(g)  N2O4(g)
2H2(g) + O2(g)  2H2O(g)
2HCl(g)  H2(g) + Cl2(g)
NOCl2(g)  NO(g) + Cl2(g)
23.
Assume the following reaction is at equilibrium:
2HBr(g)  H2(g)+ Br2(g)
ΔHo = +72 kJ
How do the FINAL concentrations compare with those of the ORIGINAL equilibrium,
and in which direction does the reaction shift to reach the NEW equilibrium if the
temperature is increased?
[H2]
increase
no change
decrease
[Br2]
increase
no change
decrease
[HBr]
increase
no change
decrease
What is the effect of adding a CATALYST to the reaction? None.
What is the effect of decreasing the volume to one-half? None. Two moles of gas going
to two moles of gas.
What is the effect of adding more H2? Bromine down, HBr up.
24.
The following reactants were combined in a 1.0 L reaction vessel:
2NO(g) + O2(g)  2NO2(g)
Kc = 1.20
After a short period, the concentrations of reactants and products were found to be as
follows:
[NO] = 1.0M, [O2] = 1.0M, [NO2] = 5.1M.
Given these concentrations, what is the value for Q? Comment on equilibrium.
Q = [5.1]2/[1.0]2[1.0] = 26.01 (Greater than Kc so equilibrium will shift toward reactants)
25.
The following reaction has Kc = 7.35E-24 at 400 K.
2SO3(g)  2SO2(g)+ O2(g)
Ho = +197 kJ
What can be said about the value of Kc at 800 K?
Kc is half as great as 7.35E-24
Kc is twice as great as 7.35E-24
Kc is greater than 7.35E-24
Kc remains constant at 7.35E-24
Kc is less than 7.35E-24