what is Enthalpy

Enthalpy is the total heat content of a thermodynamic system; it is the sum of the internal energy plus the product of pressure and volume,

mathematically,

H = U + PV...............................................................................................1

where H is the enthalpy

U internal energy

P is the pressure of the gas

V is the volume of the gas.

 the SI unit for enthalpy is joules (J)

DIFFERENTIATING THE ABOVE EQUATION WE GET

δH = δU + δ(PV) .......................................................................................2

δH = δU+ PδV+VδP

but δP =0

thus

δH = δU+ PδV........................................................................................3

from 1^st law of thermodynamics

 but dW=PdV( work done)

this implies that

δQ=δU +PδV..........................................................................................4

δU=δQ – PδV...........................................................................................5

Substituting (5) into (3) we get

δH =δQ

Meaning change in enthalpy is equal to change n internal energy

for a closed system, change in internal energy enthalpy is equal to heat added to the system,