An endothermic reaction is a type of chemical reaction in which the system absorbs energy (usually in the form of heat) from the surroundings. Because energy is taken in, the surroundings become colder during the reaction.
Key Features:
- Energy of the products is higher than the reactants.
- Heat is absorbed to make the reaction occur.
- Often feels cold to touch.
Examples of Endothermic Reactions:
- Photosynthesis – Plants absorb sunlight to convert carbon dioxide and water into glucose.
- Dissolving salts like NH₄Cl or KCl in water – the solution becomes cold.
- Electrolysis of water – energy is absorbed to split water into hydrogen and oxygen gases.
- Cooking an egg – heat is absorbed to change its structure.
Comparison with Exothermic Reactions:
- Exothermic: Release heat, surroundings warm up (e.g., combustion).
- Endothermic: Absorb heat, surroundings cool down (e.g., photosynthesis).
In short: An endothermic reaction requires energy input to proceed, so it absorbs heat from its surroundings.