AP Chemistry Review Questions - Chemical Equilibrium

Indicate the mass expression for the following reaction:

3Y₂(g) + X₂(g) ↔ 2XY₃
Determine the equilibrium constant for the system 2XY₃ ↔ 2X + 3Y₂ at 25°C. The concentrations are shown here: [XY₃] = 1.23 x 10^-2 M, [X] = 2.50 x 10^-2 M, [Y₂] = 3.75 x 10^-2 M
1. 2.18 x 10^-4
2. 3.30 x 10^-8
3. 7.19 x 10^-3
4. 9.81 x 10^-6
5. None of these
One mole of gaseous HA is placed in a one liter container. At equilibrium it is 18% dissociated according to the equation shown here:

2HA ↔ 2H + A₂

Determine the equilibrium constant.
1. K = 0.82
2. K = 0.0071
3. K = 0.0043
4. K = 0.0094
5. K = 0.0012
You are given a box containing NH₃, N₂, and H₂ at equilibrium at 1000°C. Analysis of the contents shows that the concentration of NH₃ is 0.102 mole/liter, N₂ is 1.03 moles/liter, and H₂ is 1.62 moles/liter. Calculate K for the reaction:
2NH₃(g) ↔ N₂(g) + 3H₂(g)
1. 2.37 x 10^-3
2. 4.21 x 10²
3. 3.89 x 10^-4
4. 3.89 x 10⁴
5. 9.02 x 10^-6
Consider the following equilibrium:

X₂(g) + Y₂(g) ↔ 2XY(g) + energy

Addition of XY(g) will:
1. Cause [X₂] to increase
2. Drive the reaction toward the right
3. Cause the energy of the system to increase
4. Cause [Y₂] to decrease
5. Two of these occur
Consider the following equilibrium:

X₂(g) + Y₂(g) ↔ 2XY(g) + energy

Heating the system will:
1. Cause [X₂] to decrease
2. Drive the reaction toward the right
3. Cause [Y₂] to decrease
4. Cause [XY] to decrease
5. Two of these occur
Which of the following is always true for a reaction whose value for K is 4.4 x 10⁴?
1. The reaction proceeds far to the right
2. The reaction proceeds far to the left
3. The reaction occurs quickly
4. The reaction occurs slowly
5. Two of these
Imagine a one liter container into which 2.0 mol samples of gaseous substances A, B, and C are introduced. A and B react according to the following equation:

A(g) + B(g) ↔ 2C(g)

If the value of K = 4.2, in what direction does the equilibrium exist?
1. Far to the right
2. Slightly to the right
3. Far to the left
4. Slightly to the left
5. The reaction is at equilibrium
Imagine a one liter container into which 2.0 mol samples of gaseous substances A, B, and C are introduced. A and B react according to the following equation:

A(g) + B(g) ↔ 2C(g)

If K = 2.68 for this reaction, what is the equilibrium concentration of C?
1. 2.02 M
2. 1.3 M
3. 2.7 M
4. 0.7 M
5. None of these
Imagine a one liter container into which 2.0 mol samples of gaseous substances A, B, and C are introduced. A and B react according to the following equation:

A(g) + B(g) ↔ 2C(g)

An increase in the temperature of the system would:
1. Drive the reaction to the right
2. Drive the reaction to the left
3. Have no effect on the reaction
4. The effect cannot be determined
For the reaction forming ammonia,

3H₂(g) + N₂(g) ↔ 2NH₃(g)

What effect will increasing the pressure by decreasing the volume of the system have on this system at equilibrium?
1. It will favor the formation of more ammonia
2. It will shift the equilibrium to the left
3. The [H₂] will increase
4. The [N₂] will increase
5. It will have no effect on the equilibrium concentrations
If the formation of ammonia, shown below, is exothermic at 25°C, what will be the effect of increasing the temperature of the system?

3H₂(g) + N₂(g) ↔ 2NH₃(g)
1. The equilibrium will shift to the right
2. The value of K will increase
3. The [H₂] will decrease
4. The value of K will decrease
5. Equilibrium is dependent on initial concentrations and equation stoichiometry, not on temperature. There will be no change.