A catalyst is a substance that increases the rate of a chemical reaction by lowering the activation energy without being consumed in the reaction. However, it is important to note that a catalyst does not affect the equilibrium position of a reaction. It only accelerates the rate at which the reaction reaches equilibrium. This means that the equilibrium constant Kc remains unchanged with the addition of a catalyst.Since the equilibrium constant remains the same, there is no need to calculate the change in equilibrium concentrations of products and reactants after adding a catalyst. The concentrations will still follow the same equilibrium expression as before.For example, let's consider the redox reaction between hydrogen peroxide H2O2 and iodide ions I- to form water H2O and iodine I2 :2 H2O2 aq + 2 I- aq 2 H2O l + I2 aq Suppose the equilibrium constant Kc for this reaction is 100. If a catalyst, such as iron III ions Fe3+ , is added to the reaction, it will increase the rate at which the reaction reaches equilibrium, but the Kc value will still remain 100.To reiterate, a catalyst does not shift the equilibrium position of a reaction. It only speeds up the rate at which the reaction reaches equilibrium. The equilibrium concentrations of products and reactants, as well as the Kc value, remain unchanged with the addition of a catalyst.