Chemistry Unit 2.5 - Exothermic and Endothermic Reactions

Chemistry Unit 2.5 - Exothermic and Endothermic Reactions

1. Chemical reactions involve energy transfers

   • Many chemical reactions involve the release of energy
   • For other chemical reactions, energy must be supplied

2. When chemical reactions occur, energy is transferred to or from the surroundings

3. Exothermic reaction

   • One that transfers energy to the surroundings
   • Examples include combustion, many oxidisation reactions and neutralisation
   • Everyday uses of exothermic reactions include self-heating cans (e.g. for coffee) and hand warmers

4. Endothermic reaction

   • One that takes in energy from the surroundings
   • Examples include thermal decompositions
   • Some sports-injury packs are based on endothermic reactions

5. If a reversible reaction is exothermic in one direction it is endothermic in the opposite direction

   • The same amount of energy is transferred in each case