Q.• Which parameter, equilibrium constant or activation energy, decides the rate of a chemical reaction?
• What is the influence of a catalyst on activation energy?

An enzyme is a biological catalyst, usually a protein, that increases the rate of a specific reaction by lowering its activation energy, while remaining chemically unchanged itself.

Living cells carry out thousands of chemical reactions that, left uncatalysed, would proceed far too slowly to sustain life. Enzymes solve this problem: each enzyme is a large, three-dimensionally folded molecule — the overwhelming majority are proteins, though a small class of catalytic RNA molecules called ribozymes also exists — with a specific region called the active site. The active site binds a particular substrate (or substrates) with high specificity, forming an enzyme-substrate complex that stabilises the transition state of the reaction. This lowers the activation energy (the energy barrier) that must be overcome for the reaction to proceed, so the reaction happens many orders of magnitude faster than it would without the enzyme. Crucially, the enzyme itself is not consumed or permanently altered by the reaction — once the product is released, the same enzyme molecule is free to catalyse the reaction again with a new substr …