Which of the following statements is not true? (A)- The action of a catalyst is not specific. (B)- The catalyst does not alter the equilibrium. (C)- A small amount of catalyst is sufficient to catalyse large amounts of reactants. (D)- The catalyst initiates the reaction.
Hint: Catalyst is a substance that accelerates the rate of a reaction without undergoing any change in its amount or chemical composition at the end of the reaction. The phenomenon of increase in the rate of a reaction with the addition of a catalyst is called catalysis.
Complete answer: Rate of a reaction generally increases by many folds after the addition of a catalyst. Catalyst remains unchanged in quantity and chemical composition after the completion of a reaction. Let us have a look at some of the characteristics of a catalyst: Catalysts are generally specific in action. Some biological catalysts like enzymes are highly specific in nature. However, the specificity of catalysts is not fixed. Some catalysts may catalyse a range of reactions. The catalyst does not change the position of equilibrium in a reaction. The equilibrium of a reaction remains unaltered in the presence of the catalyst. Generally, only a small quantity of a catalyst is required to catalyze a reaction. Just a little amount of catalyst is capable of taking a large amount of reactants to completion within a small interval of time. However, it has been observed that the rate of some homogeneous catalytic reactions, where the reactant and catalyst are in the same phase, depends on the concentration of the catalyst. Rate of the reactions catalyzed by solid catalysts depends on the surface area of the catalyst. The catalyst only speeds up the reaction which is already occurring however slowly. The catalyst does not initiate it. The reaction in the presence of a catalyst proceeds through the path which needs lesser activation energy.
Based on the above discussion, we can say that the most appropriate answer is option (D).
Note: We are likely to get confused between options (A) and (D). Note that not all catalysts are specific in their action and catalysts never initiate a reaction. So, out of the two options, the most acceptable answer will be option (D).