- Enthalpy Change is the heat energy transfered in a reaction at constant pressure (kJ mol -1 )
Reactions can be either exothermic or endothermic. Exothermic is reactions that gives out heat (energy). Endothermic is reactions that take in heat (energy)
When a reaction is exothermic, ΔH (enthalpy change) is negative
When a reaction is endothermic, ΔH is positive
Reactions are all about breaking/making bonds -
Energy is required when you break bonds, so making bonds is endothermic
Energy is given out when you make bonds, so making bonds is exothermic
Mean bond enthalpies are not exact
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