When heat energy of 1500 Joules, is supplied to a gas at constant pressure $2.1\times {10}^5\mathrm{N}\text{}/\text{}{\mathrm{m}}^2$ , there was an increase in its volume equal to $2.5\times {10}^{-3}{\mathrm{m}}^3$ . The increase in internal energy of the gas in Joules is