Exothermic and Endothermic Changes:
An exothermic reaction is one where energy (heat) is given out causing a temperature rise in the surroundings. The temperature of the reaction mixture rises. The container feels hot. Examples of exothermic reactions include:
- Combustion of fuels
- Rusting of iron
- Corrosion of metals
- Respiration
- Neutralization reaction
An endothermic reaction is one where energy (heat) is taken in causing a temperature drop in the surroundings. The temperature of the reaction mixture falls. The container feels cold. Examples of endothermic reactions include:
- Photosynthesis
- Thermal decomposition
The amount of energy involved in a reaction is known as he heat change or the enthalpy change of the reaction. ΔH for an exothermic reaction is negative. This is because chemicals have lost energy to the surrounding. ΔH for an endothermic reaction is positive. This is because the chemicals gain energy from the surroundings.