Types of Chemical Reactions Chemical reactions involve the breaking and forming of new chemical bonds between atoms or molecules. Based on the energy changes in...
Chemical reactions involve the breaking and forming of new chemical bonds between atoms or molecules. Based on the energy changes involved, reactions can be classified as:
Exothermic reactions release energy to the surroundings, usually as heat. The products have lower overall energy than the reactants. For example, combustion reactions like burning fuels are exothermic.
Endothermic reactions absorb energy from the surroundings. The products have higher energy than the reactants. Examples include photosynthesis and melting of solid substances.
The energy changes in a chemical reaction can be represented by a reaction profile, which shows the relative energies of reactants, products, and the activation energy barrier.
The activation energy (Ea) is the minimum energy required to initiate the reaction by breaking bonds in the reactants. Once this barrier is overcome, the reaction proceeds, and energy is either released (exothermic) or absorbed (endothermic).
Bond breaking in reactants requires an energy input, while bond formation in products releases energy. The overall energy change depends on the balance between energy absorbed for bond breaking and energy released for bond forming.
Chemical reactions can be harnessed to generate electricity in devices like chemical cells (batteries) and fuel cells. In a fuel cell, hydrogen and oxygen react to produce water, generating an electrical current in the process.
For more details on chemical reactions and energy changes, refer to the BBC Bitesize resources and official exam board specifications from OCR, AQA, Edexcel, and WJEC.