Hi,

Enthalpy means

h = u + p.v

When,

we give heat dq to a closed system at constant pressure p

then

change in enthalpy dh = dq,

where dq = du + p.dv

but here only du remains in system,

while p.dv is the part which is spended in doing work.

Then "Why do we include p.dv in the enthalpy?"

 

--------------------------------------------------

where---

h is enthalpy, u is Internal energy of the System,

p is pressure of the system,

v is Volume of the system

--and system is of Closed Type.

because that is part of the enthalpy of the system. if you work out the units you will find that pressure times volume gives you an energy.