AP Chemistry · Topic 7.2
Direction of Reversible Reactions Practice
Part of Equilibrium.(TRA-6.B)
Practice questions
10
Sample questions
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Sample 1difficulty 2/5
For a reaction A(g) <-> B(g) at equilibrium, K = 4.0. A new mixture has [A] = 0.20 M and [B] = 0.10 M.
Which direction will the system shift to reach equilibrium?
- A
Reverse, because Q = 0.5 < K
- Bcheck_circle
Forward, because Q = 0.5 < K
- C
No shift, because Q = K
- D
Forward, because Q > K
Why
Q = [B]/[A] = 0.10/0.20 = 0.5. Since Q < K, the reaction proceeds in the forward direction to make more products.
- A
Sample 2difficulty 2/5
A reaction at equilibrium can be perturbed by all EXCEPT
- Acheck_circle
Adding inert gas at constant V
- B
Adding reactant
- C
Changing T
- D
Removing product
Why
Inert gas at constant V doesn't change partial pressures of reactive species; no shift.
- A
Sample 3difficulty 2/5
For the reaction A(g) <-> B(g), [A] and [B] vs time are shown.
Which statement best describes the system at the dashed line?
- A
[A] = [B]
- B
K = 0
- Ccheck_circle
Forward and reverse rates are equal
- D
All A has been converted to B
Why
Equilibrium is defined by equal forward and reverse rates, after which concentrations stop changing. The two concentrations need not be equal.
- A
Sample 4difficulty 3/5
Which describes the reactions in mixtures A and B?
- A
A: net reverse; B: net forward
- B
Neither shifts
- C
Both go forward
- Dcheck_circle
A: net forward; B: net reverse
Why
A is to the left of K (Q < K), so it shifts forward (toward products). B is to the right (Q > K), so it shifts reverse.
- A
Sample 5difficulty 3/5
If Q < K, the reaction
- A
Is at equilibrium
- Bcheck_circle
Shifts right (toward products)
- C
Shifts left (toward reactants)
- D
Stops
Why
Q < K means too few products → forward direction proceeds.
- A