Question

Derive the following statement.

"Enthalpy change = heat capacity change"

Answer 1

At constant pressure, the system is either kept open to the atmosphere or confined within a container on which a constant external pressure is exerted and under these conditions the volume of the system changes. The thermal change at a constant pressure not only involves the change in the internal energy of the system but also the work performed either in expansion or contraction of the system.

(work)

If ‘W’ is only pressure-volume work, then

As enthalpy or heat content is defined by .

So we have,

At constant pressure, the heat of the reaction is exactly equal to the enthalpy change, , of the reacting system