- Reactant
- Inhibitor
- Catalyst
- Solvent
A catalyst is a substance that accelerates a chemical reaction by providing an alternative reaction pathway with lower activation energy, while itself remaining chemically unchanged and unconsumed at the end. This property allows catalysts to be used repeatedly, making them invaluable in industrial processes. Catalysts work by temporarily interacting with reactants, forming intermediate complexes that decompose to yield products and regenerate the catalyst. They do not alter the thermodynamics (equilibrium constant) of reactions—only the kinetics. Catalysis can be homogeneous (same phase as reactants), heterogeneous (different phase, typically solid catalyst with gaseous/liquid reactants), or enzymatic (biological catalysts). Examples include iron in the Haber process (ammonia synthesis), platinum in catalytic converters, and enzymes in living organisms. The term was coined by Jöns Jacob Berzelius in 1835. Inhibitors do the opposite—slow reactions. Understanding catalysis is crucial for chemical manufacturing, environmental protection (emissions control), and biochemistry, where enzymes catalyze virtually all metabolic reactions with remarkable specificity and efficiency.
