AQA Y12 What is the formal definition of a catalyst? Open clue This substance speeds up a reaction without being consumed itself. A A substance that increases the ultimate yield of products in a reversible reaction. B A substance that initiates a chemical reaction that would otherwise be thermodynamically impossible. C A substance that raises the kinetic energy of reactant particles to trigger a reaction. D A substance that increases the rate of a reaction without being chemically changed or used up in the final overall process. Next question Report question