Energy Equations

ENERGY EQUATIONS

Mainly, the energy equations are internal energy, enthalpy and entropy.

1. Internal Energy

We know that the internal energy

du = Tds - pdv

Let the entropy (s) is the function of temperature (T) and specific volume (v).

From equation (5.66), the internal energy in terms of measurable properties such as p, v, T and Cv can be determined.

2. Enthalpy Relations

We know that from first law of thermodynamics

Enthalpy, dh = Tds + vdp [from equation (5.57)]

Let the entropy (s) is the function of temperature (T) and specific volume (v).

i.e. s = f(T, p)

Substituting ds value in dh equation,

The above equation (5.68) appears in the form of dh = CpdT + Constant

So, Cp can be written as

From Maxwell equations,

From equation (5.70), the enthalpy in terms of measurable properties such as p, v, T and Cp can be calculated.