Changes around us, heat, light, catalyst

Chemical reactions can occur through different means such as heat, light, or catalysts. Reactions caused by heat are called thermochemical reactions, such as cooking food or producing quicklime. Reactions triggered by light, like photosynthesis, are called photochemical reactions. Catalysts speed up reactions without being used up themselves, such as yeast in fermentation or iron in the Haber process to produce ammonia. Catalyst-induced reactions are termed catalytic reactions.