Which of the following changes would decrease the rate of a reaction? addition of a catalyst increasing the concentration of reactants decreasing the concentration of products additional heat to an exothermic reaction

additional heat to an exothermic reaction

Explanation: Any change in the equilibrium is studied on the basis of Le-Chatelier's principle.

This principle states that if there is any change in the variables of the reaction, the equilibrium will shift in the direction to minimize the effect.

1. Addition of  a catalyst

Role of catalyst is to attain the equilibrium quickly without disturbing the state of equilibrium. Hence, addition of catalyst will not change the equilibrium of the reaction.  

2. increasing the concentration of reactants

If the concentration of reactants is increased so according to the Le-Chatelier's principle, the equilibrium will shift in the direction where decrease of concentration of reactants take place. Therefore, the equilibrium will shift in the forward direction and rate will increase.

3.  decreasing the concentration of products

If the concentration of products is decreased, so according to the Le-Chatelier's principle, the equilibrium will shift in the direction where increase of concentration of products take place. Therefore, the equilibrium will shift n the forward direction   and rate will increase.

4. additional heat to an exothermic reaction

If the temperature in the exothermic reaction is increased, according to the Le-Chatlier's principle, the equilibrium will shift in the direction where the extra heat gets consumed that is in the direction of endothermic recation. Thus the equilibrium will shift in backward direction and rate will decrease.Therefore, the equilibrium will shift in the left direction and thus the rate will decrease.