Unit 5 - Chemical energetics
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Exothermic reaction
A reaction that gives out energy into the surroundings creating a temperature increase
Endothermic reaction
A reaction that takes in energy from the surroundings causing a temperature decrease
Examples of exothermic reactions
• Freezing water • Combustion • neutralization reactions • Metal displacement reactions • Respiration
Examples of endothermic reactions
• Electrolysis • Melting of ice • Thermal decomposition • Cracking • Photosynthesis
Activation energy
The minimum amount of energy that particles need to have when they collide if they are going to react
Enthalpy change
The overall energy change of a reaction
Unit of enthalpy change
kJ/mol
Bond energy in exothermic reactions
The energy released when bond making is greater than the energy required to form new bonds - the surplus energy is released
Bond energy in endothermic reactions
The energy need to break bonds is greater than the energy released when new bonds form - energy must be absorbed