What is a catalyst and how does it work?

A catalyst is a substance that increases reaction rate without being consumed in the overall reaction. It works by providing an alternative reaction pathway with lower activation energy. The catalyst participates in intermediate steps but is regenerated. Catalysts do not change equilibrium position - they only help reach equilibrium faster. Types include homogeneous (same phase as reactants) and heterogeneous (different phase, typically solid catalyst with fluid reactants).