Air at 140 kPa and 27 °C is contained in the cylinder of a piston-cylinder devic

Question

Air at 140 kPa and 27 °C is contained in the cylinder of a piston-cylinder device. At this initial position, the piston is resting on a set of stops, and the volume that the air occupies is 0.4 m^3. The mass of the piston is such that a pressure of 233 kPa is required to move it, and when it does move, the pressure inside the cylinder remains constant. Energy is added as heat to the air until the volume occupied by the air doubles. Determine (a) the temperature, (b) the work done by the air on the piston, and (c) the total amount of energy transferred to the air when the piston is in this new position.

Explanation / Answer

P1 = 140 kPa P2 = 233 kPa V1 = 0.4 m^3 V2 = 0.8 m^3 T1 =300 K (a) P1V1/T1 = P2V2/T2 T2 = 998.57 K or 725.57 °C b) P(dv) = 140 x 10^3 *(.4) = 56 kJ c) the total amount of energy transferred to the air when the piston is in this new position = ncp*dT n = P1V1/RT1 n = (140 * 10^3 * 0.4)/(8.314 * 300) = 22.45 moles n * Cp* dT = 22.45 * 0.029 * (998.57-300) = 454.80 kJ

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