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?
1. decreasing the temperature
2. removing the product
3. adding more reactant
4. increasing the pressure
To increase the amount of reactant at equilibrium in this reaction, you can make the following changes:
1. Increasing the temperature: According to Le Chatelier's principle, increasing the temperature will favor the endothermic direction of the reaction. In this case, increasing the temperature will favor the reaction going to the right, resulting in more reactant at equilibrium.
2. Removing the product: By removing the product (Cl2), you are essentially decreasing its concentration, which will shift the equilibrium towards the reactant side in order to restore the equilibrium. This will result in an increase in the amount of reactant.
3. Adding more reactant: By adding more PCl5, you are increasing its concentration, which will shift the equilibrium towards the product side in order to restore the equilibrium. This will result in an increase in the amount of reactant being converted to product.
4. Increasing the pressure: Increasing the pressure of the system will compress the gas molecules, resulting in an increase in the concentration. According to Le Chatelier's principle, increasing the pressure will favor the direction with fewer moles of gas. In this case, the reaction will favor the product side and more reactant will be converted to product.
To increase the amount of reactant at equilibrium in this reaction, you can make the following changes:
1. Decreasing the temperature: According to Le Chatelier's principle, decreasing the temperature of an exothermic reaction (heat-releasing) will shift the equilibrium towards the reactants. So, in this case, decreasing the temperature would increase the amount of reactant at equilibrium.
2. Removing the product: If you remove one of the products (in this case, Cl2), the reaction will try to compensate for the loss by shifting towards the side of the reactants. As a result, the amount of reactant at equilibrium will increase.
3. Adding more reactant: According to Le Chatelier's principle, increasing the concentration of one of the reactants will cause the equilibrium to shift in the direction that consumes that reactant. Thus, adding more PCl5 would result in an increase in the amount of reactant at equilibrium.
4. Increasing the pressure: Increasing the pressure of a reaction that involves gaseous substances will cause the equilibrium to shift in the direction that reduces the number of gas molecules. In this case, increasing the pressure would shift the equilibrium towards the reactants (PCl5 and PCl3), leading to an increase in the amount of reactant at equilibrium.
Therefore, all of the listed options can be used to increase the amount of reactant at equilibrium in this reaction.
To determine how the changes listed would affect the amount of reactant at equilibrium in the reaction, we need to understand Le Chatelier's principle. According to Le Chatelier's principle, a system at equilibrium will respond to changes by shifting in a direction that counters the change. Let's analyze each change listed:
1. Decreasing the temperature: According to Le Chatelier's principle, if the temperature is decreased, the system will shift in the direction that produces heat. Since the forward reaction is exothermic (heat is a product), it will be favored by decreasing the temperature. Therefore, the amount of reactant at equilibrium will increase. In this case, the answer is YES.
2. Removing the product: By removing the product (Cl2), the equilibrium will shift to the right to replace the lost product. As a result, more reactant (PCl5) will be consumed to produce more product to maintain equilibrium. Therefore, the amount of reactant at equilibrium will decrease. In this case, the answer is NO.
3. Adding more reactant: According to Le Chatelier's principle, if more reactant is added, the equilibrium will shift in the direction that consumes the added reactant, trying to re-establish equilibrium. In this case, adding more PCl5 will result in the reaction shifting to the right, producing more PCl3 and Cl2, thus decreasing the amount of reactant at equilibrium. Therefore, the answer is NO.
4. Increasing the pressure: This reaction has a decrease in the number of moles of gas on the product side. According to Le Chatelier's principle, in order to counteract an increase in pressure, the reaction will shift in the direction that produces fewer moles of gas. In this case, increasing the pressure will favor the forward reaction (to the right) to decrease the number of gas molecules, thus consuming more reactant at equilibrium. Therefore, the amount of reactant at equilibrium will decrease. In this case, the answer is NO.
Therefore, the only change that will increase the amount of reactant at equilibrium in this reaction is decreasing the temperature (1).