jasoncurious

If PV ln (V2/V1) were to be used, it doesn't make sense. The gas expands suddenly, not in a quasi-static manner. I don't know what other equation can be used.

A gas is confined in a cylinder by a piston. The initial pressure of the gas is 7 bar(700kPa), and the volume is 0.10m^3. The piston is held in place by latches in the cylinder wall.The whole apparatus is placed in a total vacuum. What is the energy change of the apparatus if the restraining latches are removed so that the gas suddenly expands to double its initial volume, the piston striking other latches at the end of the process? Data known: P(initial) = 700kPa V(initial) = 0.10m^3 V(final) = 0.2m^3 My analysis: Since the gas suddenly expands (not a quasi-equilibrium process), the PV ln (V2/V1) equation cannot be used. But still, my lecturer gave me zero. I want to know the right way to solve this problem. God bless you all.

An air compressor is used to compress air from 100kPa and 30°C to 800kPa at a rate of 120kg/min. By having the inter-cooling feature the compression is done at constant temperature of 30°C. Calculate the power required for the compression. Known data: P(initial)=100kPa P(final)=800kPa Temperature(constant)=30°C Mass flow rate=120kg/min=2kg/s My friends applied the formula of work done for isothermal process(since the compression is done at constant temperature of 30°C): W=RTln(P1/P2) *R used is 0.2870 Their assumption is that Work(in)=Work(out). May I know what happened to the mh1 in the usual energy balance for open system? Under what condition can we make the assumption Work(in)=Work(out)?