Topic: Thermodynamics
Air at 100 kPa, 2°C occupies a 10 liter piston-cylinder device that is arranged to maintain constant air pressure. This device is now heated until its volume is 20 liters. The work produced by the air is
- A. 20 kJ
- B. 10 kJ
- C. 2 kJ
- D. 1 kJ
Answer: D. 1 kJ
Explanation: The process is isobaric (constant pressure). The work done by a gas during a constant pressure process is given by $W = P(V_2 - V_1)$. The pressure is $P = 100$ kPa = $100 \times 10^3$ Pa. The initial volume is $V_1 = 10$ liters = $10 \times 10^{-3}$ $m³$, and the final volume is $V_2 = 20$ liters = $20 \times 10^{-3}$ $m³$. Work done $W = 100 \times 10^3 \times (20 \times 10^{-3} - 10 \times 10^{-3}) = 100 \times 10^3 \times 10 \times 10^{-3} = 1000$ J = 1 kJ.