Enthalpies of reaction - thermochemistry

We know that the reaction enthalpy is identical to the reaction heat at constant pressure. The properties and means of determining these reaction heats make up hermochemistry. 

The development of knowledge of reaction enthalpies is closely linked to that of reaction heats, and therefore to calorimetry and thermochemistry. 

Experimental measurement of a reaction heat at constant pressure at a temperature determined by calorimetry requires the measurement to respect a set of essential precautions  

These conditions mean that direct measurement of the heat of a large number of reactions is still tricky, and therefore a significant amount of data still needs to be improved. 

If we know the enthalpy at a temperature To, it is easy to use a relation such as [4.7] to calculate that enthalpy at any temperature T, provided we know the variations of the molar specific heat capacities of the reaction components between temperatures To and T and the enthalpies of state change of those components within that temperature range. 

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