JNTU B.Tech III THERMODYNAMICS FOR PETROLEUM ENGINEERS Previous Question Paper (March - 2021 - R16)

The First Law of Thermodynamics states that energy can neither be created nor destroyed, only transformed from one form to another. For a closed system undergoing a process, it is expressed as the conservation of energy principle:

A thermodynamic state function is a property whose value depends only on the current state of the system (e.g., pressure, temperature, volume, internal energy, enthalpy) and is independent of the path taken to reach that state. In contrast, a path function depends on the specific process or path taken to change the system from one state to another; heat (Q) and work (W) are classic examples of path functions.

Given: m = 1 kg, T1 = 300 K, P = 1 bar = 10^5 Pa. Since the process is at constant pressure, V2 = 3V1 and T2 = 3T1 = 900 K. Assuming air behaves as an ideal gas with M = 28.97 g/mol, the number of moles n = 1000 / 28.97 = 34.52 mol.

1. Work (W): For a constant pressure process, W = P(V2 - V1) = nR(T2 - T1). Using R = 8.314 J/mol·K, W = 34.52 * 8.314 * (900 - 300) = 172,175 J = 172.18 kJ.
2. Enthalpy Change (ΔH): ΔH = n * Cp * (T2 - T1). Given Cp = 29 J/mol·K, ΔH = 34.52 * 29 * (900 - 300) = 600,648 J = 600.65 kJ.
3. Internal Energy Change (ΔU): Using Cv = Cp - R = 29 - 8.314 = 20.686 J/mol·K, ΔU = n * Cv * (T2 - T1) = 34.52 * 20.686 * 600 = 428,473 J = 428.47 kJ.
4. Heat (Q): For constant pressure, Q = ΔH = 600.65 kJ.