[UPSC CSE 2026] Thermodynamics (Q1, 10M)

What are the limitations of the first law of thermodynamics? One mole of a gas, assumed to be perfect, at 0\text{ }^\circ\text{C} is heated at constant pressure till its volume is twice its initial value. Calculate the amount of heat absorbed. Given, C_v = 20\cdot 9\text{ J}\cdot\text{mol}^{-1}\cdot\text{K}^{-1} and R = 8\cdot 3\text{ J}\cdot\text{mol}^{-1}\cdot\text{K}^{-1}.