AP Chemistry Institute
Gaseous Equilibrium Problem Set
1.
An equilibrium mixture for the reaction: 2 H2S(gas) <====> 2 H2(gas) + S2(gas)
had 1.0 mole of H2S, 0.20 moles of H2, and 0.80 moles of S2 in a 2.0-liter vessel. Kc equals:
-3
-3
A) 4.0 x 10 M;
B) 8.0 x 10 M;
C) 0.16 M;
D) 0.016 M;
E) 0.032 M
2.
Given: 2 A + B <===> 3 C + D (all gases). If equal numbers of moles of A and B are added to an
empty flask, then the following must be true when equilibrium is attained:
A) [D] = [B];
B) [A] = [B];
C) [A] > [B]; D ) [A] < [B]; E) [A] + [B] > [C] + [D].
3.
KP for the equilibrium, NH3(gas) + H2S(gas) <===> NH4HS(solid), is equal to:
[NH4HS]
A) --------------[NH3][H2S]
D) PNH4HS - PNH3 - PH2S
PNH4HS
B) PNH3 x PH2S
C) ----------------------PNH3 x PH2S
E) none of these.
4.
At a given temperature the equilibrium constant is 5.0 for the following reaction:
CO + H2O <=====> CO2 + H2 (all gases)
Analysis showed that an equilibrium mixture at this temperature contained 0.90 mole of carbon
monoxide, 0.25 mole of water vapor, and 0.50 mole of hydrogen gas in a 5.0-liter container. How many
moles of carbon dioxide were there in the equilibrium mixture?
A) 2.3;
B) 0.010;
C) 0.45;
D) 5.0;
E) 0.90
5.
Under the same conditions as in Question #4, 0.40 moles of H2 and 0.40 moles of carbon dioxide were
placed in a 1.0-liter vessel. What will be the equilibrium concentration of water vapor?
A) 0.28 M;
B) 0.40 M;
C) 0.80 M;
D) 0.12 M;
E) none of these.
6.
Which of the following reactions has the least tendency to go to completion?
+27
A) 2 H2(gas) + O2(gas) <=====> 2 H2O(liquid)
K = 1.7 x 10 ;
-31
B) N2(gas) + O2(gas)
<====> 2 NO(gas)
K = 5.0 x 10 ;
+16
C)
H2(gas) + Cl2(gas) <==> 2 HCl(gas)
K = 3.2 x 10 ;
-13
D) 2 HF(gas)
<=====> H2(gas) + F2(gas)
K = 1.0 x 10 ;
-4
E) 2 NOCl(gas) <====> 2 NO(gas) + Cl2(gas)
K = 4.7 x 10
7.
The system 2 NO(gas) + Cl2(gas) <===> 2 NOCl(gas) at a given T contains at equilibrium 1.000 M
NO, 0.1000 M Cl2, and 1.000 M NOCl, which yields KC = 10.00. How many moles per liter of NO need
to be added to decrease the [Cl2] to 0.0500 M?
A) 0.656;
B) 0.099;
C) 0.328;
D) 0.149;
E) 0.050
8.
At 30 C an equilibrium mixture of N2O4(gas) and NO2(gas) exerted a total pressure of 0.750 atm. The
partial pressure of N2O4 was 0.500 atm.
KP for the reaction N2O4(gas) <===> 2 NO2(gas) is:
A) 1.50;
B) 0.667;
C) 0.125;
D) 0.500;
E) 1.00
o
-2o
9.
What is KP at 25 C for the reaction: N2(gas) + 3 H2(gas) <===> 2 NH3(gas) based on the data from a
thermodynamics table?
2
3
5
-3
-6
A) 7.7 x 10 ;
B) 1. 08 x 10 ;
C) 5.9 x 10 ;
D) 1.3 x 10 ;
E) 1.7 x 10 .
10.
At a temperature of about 425 C, the equilibrium mixture (EQ) given below prevails:
o
H2(gas)
+
I2(gas) <=====> 2 HI(gas)
H = -9.46 kJ
EQ: 0.1000 M
0.1000 M
0.7000 M
o
If suddenly 0.0500 mole/liter of H2, 0.0500 mole/liter of I2, and 0.3500 mole/liter of HI were added, the
result would be that:
A) more HI would form;
B) more H2 and I2 would form;
C) the equilibrium would be shifted to the right;
D) heat would be absorbed by the system ;
E) no net chemical reaction would occur.
11.
o
-5
-4
What is G in kJ for a process at 25 C having K = 1.0 x 10 and Q = 1.0 x 10 ?
A) +5.70;
B)-10.0;
C) -5.70;
D) +10.0;
E) +8.31
The last set of questions deal with the following reversible reaction:
N2O5(gas) <===> 2 NO2(gas) + 1/2 O2(gas) (T = 298.15 K)
12.
13.
o
o
o
Substance
Hf , kcal/mole
Gf , kcal/mole
S , cal/mole-K
N2O5(gas)
NO2(gas)
O2(gas)
3.35
8.09
--
28.18
12.39
--
85.00
57.47
49.00
o
What is G rxn at 298.15K?
A) -15.79 kcal;
B) -11.36 kcal;
C) -3.40 kcal;
D) +16.18 kcal;
What is the approximate value of KP at 298 K?
5
2
-6
A) ~ 2 x 10 ;
B) ~ 3 x 10 ;
C) ~1 x 10 ;
D) ~ 10;
E) +28.18 kcal.
E) ~ 1
14.
According to LeChatelier's principle, an increase in T (temperature) would result in all of the following
EXCEPT:
A) an increase in the value of K;
B) an increase in the value of the specific rate constant, k;
C) an increase in the percent decomposition of N2O5;
D) an increase in the equilibrium partial pressure of oxygen;
E) an increase in the value of EA, the activation energy.
15.
What is the approximate value of KP at 373 K?
4
5
-6
A) ~ 2 x 10 ;
B) ~ 3 x 10 ;
C) ~4 x 10 ;
16.
What are the units of KP?
2
A) atm;
B) atm ;
3/2
C) atm ;
D) ~0.1;
D) atm
-1/2
;
E) ~ 1
E) atm
-1