A sample of air has volume of 400 dm3 and a pressure of 1.2 bar. What additional pressure is needed to reduce the volume to  150  dm3at 27°C?

Final pressure,P2=?Volume =150 dm3. At constant temperature,27°C:P1V1=P2V2 (Boyle's law)1.2bar×400dm3=P2×150 dm3;P2=1.2bar×400dm3150dm3or P2=3.2 bar∴ Additional pressure required = 3.2 bar - 1.2 = 2 bar