A steel reaction vessel has a movable piston that is set to allow an enclosed sample of gas expand and contract against a constant external pressure of 1.12 atm. A 2.50-g sample of PCl5 (g) is placed in this vessel at a temperature of 250°C and a pressure of 1.12 atm. The temperature is maintained at 250°C and the PCl5 partially decomposes according to the following balanced equation:
PCl5 (g) → PCl3 (g) + Cl2 (g) The final volume of the gas mixture is measured to be 0.826 L. Determine w, q, and ΔU for this sample of gas during this process.