Question

What is mean by enthalpy and entropy

Answer 1

Enthalpy is the sum of internal energy U of a system and the product of the pressure and change in volume of the system at a constant pressure.
H=U+PV
The PV term represents the mechanical work done on or by the system, and is opposite in sign to the PV-work term present within the first law of thermodynamics, ΔU=q+w.

Entropy is a measure of the disorder or randomness of a system.
ΔS equals the heat transferred reversibly between the system and its surroundings divided by T.

ΔS=qrevT=ΔHT

where the relationship qrev=ΔH holds at constant pressure.