Question

The system $$ 3 Z(g)+\mathrm{Q}(g) \rightleftharpoons 2 \mathrm{R}(g) $$ is at equilibrium when the partial pressure of \(\mathrm{Q}\) is \(0.44 \mathrm{~atm}\). Sufficient \(\mathrm{R}\) is added to increase the partial pressure of \(\mathrm{Q}\) temporarily to 1.5 atm. When equilibrium is reestablished, the partial pressure of \(\mathrm{Q}\) could be which of the following? (a) 1.5 atm (b) 1.2 atm (c) 0.80 atm (d) \(0.44 \mathrm{~atm}\) (e) \(0.40 \mathrm{~atm}\)

Short answer

Answer: The possible new partial pressure of Q when the system reaches equilibrium again could be 1.2 atm, 0.80 atm, or 0.44 atm.

Step-by-step solution

Understand Le Châtelier's Principle

Le Châtelier's Principle states that when a chemical system at equilibrium is disturbed, the system will shift its position to counteract the change and reestablish a new equilibrium. In this case, the system's equilibrium will be disturbed by adding more R.

Determine the direction of the equilibrium shift

Due to the addition of R, the chemical system will shift to counteract the added concentration. The system will shift to the left, i.e. the reverse reaction will be favored as it consumes R to produce Q and Z: $$3 Z(g) + Q(g) \leftarrow 2 R(g)$$

Determine the change in partial pressure of Q

Since the reverse reaction is favored, it is expected that the partial pressure of Q (which was increased temporarily to 1.5 atm) should decrease as the system moves towards the new equilibrium.

Choose the correct option

Based on the direction of the equilibrium shift and understanding the change expected in the partial pressure of Q, we should choose an option that represents a decreased partial pressure. Among the provided options: (a) 1.5 atm (no change in partial pressure, not feasible) (b) 1.2 atm (partial pressure has decreased, feasible) (c) 0.80 atm (partial pressure has decreased, feasible) (d) \(0.44 \mathrm{~atm}\) (initial partial pressure, feasible) (e) \(0.40 \mathrm{~atm}\) (partial pressure has decreased and is now less than the initial pressure, not feasible) Thus, the possible new partial pressure of Q when the system reaches equilibrium again could be (b) 1.2 atm, (c) 0.80 atm, or (d) \(0.44 \mathrm{~atm}\).