S = p + dp 1
(i)
Starting from Equation 1, derive an equation for the change in entropy, S, of one mole of an ideal gas when the pressure changes from an initial pressure, pi, to a final pressure, p2, and the temperature changes from an initial temperature of Ti to a final temperature of T2. Explain any assumptions you have made in deriving the equation. [5 marks]
A compressor is used to compress helium gas from an initial pressure of 100 kPa to a final pressure of 450 kPa. The temperature of the helium gas in the feed to the compressor is 300 K. The heat capacity of helium gas at constant pressure may be taken as 20.9 J/mol·K. If the compressor operates adiabatically and perfectly reversibly, what is the final temperature? [3 marks]
(ii)
(iii)
The temperature of the helium gas from the compressor in part (ii) is found to be 650 K. Calculate the efficiency of the compressor. [2 marks]