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If a system expands in volume by an amount V(m3) against a constant restraining pressure P(N/m2), a quantity PV(J) of energy is transferred as expansion work from the system to its surroundings. Suppose that the following four conditions are satisfied for a closed system: (a) the system expands against a constant pressure (so that P=0 ); (b) Ek=0; (c) Ep=0; and (d) the only work done by or on the system is expansion work. Prove that under these conditions, the energy balance simplifies to Q=H. Q2. Steam at 260C and 7.00 bar absolute is expanded through a nozele to 200C and 4.00 bar. Negligible heat is transferred from the nozale to its surroundings. The approach velocity of the steam is negligible. The specific enthalpy of steam is 2974J/kg at 260C and 7 bar and 2860kJ/kg at 200C and 4 bar. Use the open-system energy balance to calculate the exit steam velocity