Internal energy in thermodynamics
- Inter-molecular potential energy, associated with forces between the molecules.
- Molecular K.E associated with transitional and rotational velocity of each molecules.
- Intra molecular energy within the molecular/atomic structures and related forces.
Definition of Enthalpy
Definition of entropy :Entropy (S.s) represents the disorder of uncertainty of microscopic level, even yet it is used as a property at macroscopic level. Entropy is specified for every equilibrium state of a pure substance. Entropy is also mainly a function of temperature. In 1865 Rudolph Clausius first introduced the term entropy.
I hope understand the difference between enthalpy and entropy. Don't get confused. Try to understand Enthalpy vs. Entropy.
These three properties mentioned are more like mathematical entities having important physical significance. We are more interested in changes of these properties i.e. ds. du etc. rather than individual values which may depend on reference of calculation.