Use the reaction to answer the question.
heat + PCl^5(g) ⟷ PCl^3(g) + Cl^2(g)
What changes can you make to increase the amount of reactant at equilibrium in this reaction? There is only one correct answer.
1. decreasing the temperature
2. removing the product
3. adding more reactant
4. increasing the pressure
1. decreasing the temperature
To increase the amount of reactant at equilibrium in this reaction, you should add more reactant. Therefore, option 3, which states "adding more reactant," is the correct answer.
To determine which change can increase the amount of reactant at equilibrium in this reaction, we can examine Le Chatelier's principle. This principle states that a system at equilibrium will respond to any stress or change in conditions by shifting its equilibrium position in a way that reduces the effect of that stress.
In this reaction, the reactant (PCl5) is on the left side of the equation. To increase the amount of reactant at equilibrium, we need to shift the equilibrium position to the left. Let's examine each option to see which one achieves this goal.
1. Decreasing the temperature: According to Le Chatelier's principle, when the temperature is decreased, the equilibrium position will shift in the direction that produces more heat. In this case, heat is a product of the reaction (on the right side of the equation), so decreasing the temperature would actually shift the equilibrium to the right, reducing the reactant amount. Therefore, this option does not increase the amount of reactant.
2. Removing the product: Since removing the product (Cl2) decreases its concentration, the reaction would try to replenish the product by shifting the equilibrium to the right. Therefore, this option also does not increase the amount of reactant.
3. Adding more reactant: According to Le Chatelier's principle, if more reactant is added, the reaction will shift in the direction that reduces the excess reactant. This means the equilibrium position will shift to the right, increasing the product amount. However, in this case, we want to increase the reactant amount. Therefore, this option is also not correct.
4. Increasing the pressure: When the pressure is increased, the reaction will shift in the direction that reduces the total number of gas molecules. In this reaction, there are two moles of gas on the left side and two moles of gas on the right side. Therefore, increasing the pressure does not impact the equilibrium position. Hence, this option does not increase the amount of reactant.
Considering the analysis above, the correct answer is 2. Removing the product does not increase the amount of reactant at equilibrium in this reaction.