Question

Classify each chemical or physical change as an endothermic or exothermic process.

Burning a candle


Cooking an egg


Rain changing to snow


Boiling water



Combustion reaction:
CH4 + 2O2 es002-1.jpg CO2 + 2H2O + heat

Answer 1

- Burning a candle — chemical change, exothermic. (Combustion of wax releases heat and light.)
- Cooking an egg — chemical change, endothermic. (Heat is absorbed to denature proteins and drive the chemical changes.)
- Rain changing to snow — physical change (phase change), exothermic. (Freezing/releases latent heat of fusion to the surroundings.)
- Boiling water — physical change (phase change), endothermic. (Vaporization requires input of latent heat.)
- CH4 + 2 O2 → CO2 + 2 H2O + heat — chemical change, exothermic. (The reaction releases heat as shown.)