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Energy changes AS chemistry revision notes
Exothermic and endothermic reactions:
A reaction that gives out energy and warms the surroundings is exothermic.
A reaction that takes in energy and cools the surroundings in endothermic.
This can be plotted on an enthalpy level diagram:
Standard enthalpy change of combustion:
Standard enthalpy change of combustion is the enthalpy change when one mole of reactants is
burnt in oxygen in it's natural state.
The amount of energy
taken in or
given out when reactants
in the form of how they
are naturally found are burnt in one mole of oxygen.Measuring standard enthalpy change of
Standard enthalpy change of formation
Standard enthalpy change of formation is one mole of a compound is formed from it's elements.
The amount of energy given out or taken in when you alter the molecular numbers of the
reactants to make them combine to make 1 mole of the compound.