Enthalpies

In chemical reactions, if products have a different energy content compare to reactants then energy will be exchanged with surrounding. If the products have lower enthalpy than the reactants, the reaction is exothermic (Energy is given out). On the other hand, if the products have higher enthalpy than the reactants, the reaction is endothermic (Energy is absorbed).

Standard enthalpy changes

There are various factors that affect the enthalpy change in a reaction. Thus by setting Standard enthalpy (enthalpy of a reaction measured under standard condition: 25oC (298K); 1 atmosphere pressure; and 1mol of concentration) valid comparison can be made between different experiments.

There are various standard enthalpy changes you have to memorise.
Standard enthalpy of Formation
Standard enthalpy of Combustion
Standard enthalpy of Atomization
Standard enthalpy of Neutralization
Standard enthalpy of Solution
Standard enthalpy of Fusion (or Melting)
Standard enthalpy of Vaporization
Standard enthalpy of Hydrogenation

For definition of each Standard enthalpy click here

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