The Equilibrium Constant
1.
Given the reaction at equilibrium 2A + B  C + 3D, calculate the value of K if the equilibrium
concentrations are found to be [A] = 10 M, [B] = 15 M, [C] = 5 M and [D] = 25 M. (Ans: 52)
2.
At 773°C a mixture of CO(g), H2(g) and CH3OH(g) was allowed to come to equilibrium. The
following equilibrium concentration were then measured [CO] = 0.105 M, [H2] = 0.250 M,
[CH3OH] = 0.00261 M. Calculate Keq for the reaction CO(g) + 2H2(g)  CH3OH(g) (Ans: 0.398)
3.
In the reaction Fe+2(aq) + Ag+(aq)  Fe+3(aq) + Ag(s) at equilibrium the following concentrations
were found: [Fe+2] = 0.50 M, [Ag+1] = 1.0 M; [Fe+3] = 1.50 M. (a) Calculate the equilibrium
constant for the reaction. (b) If at equilibrium [Fe+2] is found to e 0.20 M and [Ag+] is 0.30 M,
what must be the concentration of Fe+3? (Ans: a) 3.0 b) 0.18 M)
4.
A substance (CD) decomposes into C and D. CD (g)  C (g) + D (g). At equilibrium the
concentration of CD is 0.17 mol/L.
(a) If the initial concentration of CD is 0.2 mol/L, what are the equilibrium concentrations of C
and D? (Ans: 0.03, 0.03)
(b) What is the K for the reaction at this temperature? (Ans: 5.3x10-3)
5.
Fluorine gas F2 reacts with hydrogen gas H2 according to the equation F2(g) + H2(g)  2HF(g)
0.50 mol of each F2 and H2 are placed in a 1.0L vessel and allowed to reach equilibrium at a
given temperature. The equilibrium concentration of HF is found to be 0.025 mol/L. What is the
value of the equilibrium constant, k for the reaction? (Ans: 2.63x10 -3)
6.
When 0.60 mol of gas X and 0.40 mol of gas Y react in a 2.0 L container to produce Z,
equilibrium is reached in which [Z] is found to be 0.080 mol/L. The reaction is
X(g) + 2Y(g)  2Z(g). Calculate the value of Keq. (Ans: 1.71)
7.
Given the equilibrium reaction A(g) + B(g)  C(g) when 1.00 mole of both A and B are placed
in a 4.0L container, the equilibrium constant is 2.5x10-5. What is the equilibrium concentration of
C? (Ans: 1.6x10-6 mol/L)
8.
Two moles of NO2(g) are injected into an evacuated 1.0 L flask. The equilibrium constant is 1.23
for 2 NO2(g)  N2O4(g). What are the equilibrium concentration of NO2 and N2O4?
(Ans: 0.72M, 0.64M)
9.
A reaction may be represented by A2(g) + B2(g)  2AB (g). At a given temperature 1.0 mol of A
and 1.0 mol of B are placed in the 2.0 L vessel. The K value for this reaction is 3.0x10 -2. What
are the equilibrium concentrations of each of the substances? (Ans: 0.46, 0.46, 0.080)
10. For the reaction 2 NH3 (g)  N2 (g) + 3 H2 (g) the K value is 16.6. At equilibrium the concentration
of H2 is 0.36 mol/L. What was the initial concentration of ammonia? (Ans: 0.26)