Question

Calculate the internal energy and enthalpy of 1kg of air occupying 0.05m

Answer 1

We will assume that gas is ideal. So, the internal energy of air

$$U=\frac{m}{M}C_VT$$

For air $M=28.96 \cdot 10^{-3}kg/mol$ and $C_V=\frac{i}{2}R=\frac{5}{2}\cdot 8.31\approx20.8\frac {J}{mol\cdot K}$

$$U=\frac{m}{M}C_VT=\frac{1}{28.96 \cdot 10^{-3}}\cdot 20.8\cdot 293=210442J$$

The enthalpy of air

$$H=U+pV=210442+2\cdot 10^6\cdot 0.05=310442J$$