Which of the following changes would increase the molar concentration of the products in any chemical reaction at equilibrium?
Increase the molar concentration of the reactants
decrease the temperature
add a catalyst
decrease the pressure
Increase the temperature
The correct answer and explanation is:
The correct answer is Increase the molar concentration of the reactants.
In a chemical reaction at equilibrium, the concentrations of reactants and products remain constant. However, when changes occur, the system adjusts to restore equilibrium. This adjustment is described by Le Chatelier’s Principle, which states that if a system at equilibrium is disturbed, it will shift to counteract that disturbance.
When the molar concentration of the reactants is increased, the system will shift toward the products to consume some of the added reactants. This shift increases the concentration of the products. This happens because the forward reaction is favored when more reactants are available, resulting in more product formation.
Other factors:
- Decrease the temperature: The effect of this depends on whether the reaction is exothermic or endothermic. For exothermic reactions, decreasing the temperature would shift the equilibrium toward the products (because heat is a product), increasing the concentration of products. For endothermic reactions, decreasing the temperature would shift the equilibrium toward the reactants, decreasing the product concentration.
- Add a catalyst: A catalyst speeds up both the forward and reverse reactions equally, but it does not change the equilibrium position. Therefore, adding a catalyst does not affect the molar concentration of products.
- Decrease the pressure: This mainly applies to reactions involving gases. If the number of gas molecules on the reactant side is greater than on the product side, decreasing the pressure will shift the equilibrium toward the product side. However, if the number of gas molecules is the same on both sides, pressure changes will have little effect.
- Increase the temperature: For endothermic reactions, increasing the temperature shifts the equilibrium toward the products, increasing product concentration. For exothermic reactions, increasing the temperature shifts the equilibrium toward the reactants, decreasing product concentration.