The Chemistry of Cold

You've twisted an instant cold pack after a sports injury, and felt it become icy cold in your hands. No refrigeration needed — just chemistry! Inside, a barrier breaks and ammonium nitrate dissolves in water. But this isn't just mixing — it's a chemical process that ABSORBS energy from its surroundings (your injured ankle). The reaction needs energy to happen, so it steals heat from whatever is nearby. This is endothermic in action — the same principle that allows plants to capture sunlight and convert it into food through photosynthesis.