Question

What is the significance of enthalpy in the second law of thermodynamics?

Answer 1

Hint: Second Law of Thermodynamics states that It is impossible to extract an amount of heat ${{Q}_{H}}$ from a hot reservoir and use it all to do work W. Some amount of heat ${{Q}_{C}}$ must be exhausted to a cold reservoir. This precludes a perfect heat engine. This law creates the concept of entropy as a physical property

Complete step-by-step solution:
Enthalpy is the sum of the internal energy and the product of the pressure and volume of a thermodynamic system. Enthalpy is an energy-like property or state function that has the dimensions of energy (and thus is calculated in joules or ergs), and its value is entirely determined by the temperature, strain, and composition of the system, not by its background.
In symbols, the enthalpy, H, equals the sum of the internal energy, E, and the product of the pressure, P, and volume, V, of the system: H = E + PV.
Enthalpy is a state function and with the help of which we can now define the heat interaction between two state points that too without depending upon the path because if it had been defined in any other way it would not signify anything, with this combination it becomes equal to the heat.

Note: The change in enthalpy observed in the constituents of a thermodynamic system as it undergoes a transformation or chemical reaction is referred to as an enthalpy change. It is the difference between the final enthalpy of the system, that is the enthalpy of the products, and the initial enthalpy of the system, that is the reactant's enthalpy.