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1. Entropy :-  A thermodynamic quantity representing the unavailability of the systems thermal energy for the conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system. it is denoted by S and the natural logarithm of the no. micro states, multiply by Boltzmann constant Kb. its SI unit is joules per kelvin.

2. Enthalpy :- A thermodynamic quantity representing total heat content of the system it is equal to internal energy of the system plus pressure and volume. it is denoted by H, and the formula for the enthalpy is given as

H(s,p)= U+pV

3. Isobar (nuclide)  :- Isobars are the atoms of different element having same no. of nucleons. it means isobars have different atomic no. but have the same mass no.

4. Isobar (thermodynamic ) :- An isobar is curve drawn through the points of equal pressure.

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