1. Equilibrium Calculations
Lesson 8

2. 1. When moles of SO2 and moles of O a 2.00 L container and allowed to reach equilibrium, the equilibrium [SO3] is M. Calculate the Keq.
are placed into
Implies initial and not equilibrium concentrations
- ICE
2SO2 (g) + O2 (g) ⇋ 2SO3 (g) I
0.400 M
0.400M
x1/2
x 2/2 C M M M E
0.100 M
0.250 M
0.300 M
Equilibrium concentrations go in the equilibrium equation!
[SO3]2
(0.3)2
Keq = =
= 36.0
[SO2]2[O2]
(0.1)2(0.25)

3. 2. 80 moles of H2 and 1. 4 moles of S are initially put in a 4
moles of H2 and 1.4 moles of S are initially put in a 4.0 L flask and allowed to reach equilibrium. Calculate the [H2] at equilibrium.
H2(g) S(s) ⇄ H2S(g) Keq= 14
I 0.20 M 0
C x x
E x x
[H2S] x
Keq = = =
[H2] x

4. x x = 1
1x = 14( x)
1x = x
1x x =
15x =
x = 0.19 M
[H2] = x
[H2] =
-note the lose of one sig fig!
[H2] = 0.01 M

5. 3. If 6. 0 moles of HI are initially put in a 3
3. If 6.0 moles of HI are initially put in a 3.00 L vessel and allowed to reach equilibrium. What is the equilibrium concentration of H2?
2HI(g) ⇄ H2(g) I2(g) Keq = I
2.0 M
0 0 C
-2x x x E
x x x
[H2][I2] x2
Keq = = =
( x)2
[HI]2

6. x2
( x)2 =
take the square root of both sides = 1 x
( x)
cross multiple
1x = x
x =
x = [H2] = 0.21 M

7. 4. The same number of moles of I2 and Cl2 are placed in a 10
4. The same number of moles of I2 and Cl2 are placed in a 10.0 L flask and allowed to reach equilibrium. If the equilibrium concentration of ICl is 0.40 M, calculate the initial number of moles of I2 and Cl2.
I2 (g) + Cl2 (g) ⇄ ICl (g) Keq =
I x x 0
C M M M
E x x M
[ICl]2
Keq =
[I2][Cl2]
0.402 =
= 10.0
(x )2

8. 0.402
(x )2
= 10.0 = x
0.4 = x
= x
x = [I2] = [Cl2] = 0.33 M
10.0 L
x mole
= mol L

9. Calculate the value of the Keq.
5. Sketch the changes in concentrations of [O2] and [N2] as equilibrium is obtained.
Calculate the value of the Keq.
4.00 M
2.80 M
[N2O4]
Time (min) 20 40
1.20 M
2.40 M
[N2][O2]2
Keq =
[N2O4]
[O2]
Keq = [1.20][2.40]2
[N2]
[2.80]
= 2.47
N2O4(g) ⇋ 2O2(g) + N2(g) I C E