Choice of pressure in using ideal gas equation

[jasoncurious]

100g of CO are contained in a weighted piston-cylinder device. Initially, the CO is at 1000kPa and 200^oC. It is then heated until 500^oC. Determine the final volume of the CO treating it as an ideal gas.

 

This is what my lecturer gave in his solution:

 

V₂=(mRT₂₎/P=(0.1kg*0.2968kPa.m³/kg.K*(500+273)K)/1000kPA

 

My question is: why is the original pressure (1000kPa) been used instead of the final pressure?

 

Thanks for your help.

 

 

 

[alpha2cen]

100g of CO are contained in a weighted piston-cylinder device. Initially, the CO is at 1000kPa and 200^oC. It is then heated until 500^oC. Determine the final volume of the CO treating it as an ideal gas.

 

This is what my lecturer gave in his solution:

 

V₂=(mRT₂₎/P=(0.1kg*0.2968kPa.m³/kg.K*(500+273)K)/1000kPA

 

My question is: why is the original pressure (1000kPa) been used instead of the final pressure?

 

Thanks for your help.

 

 

 

[jasoncurious]

So, the black one is the piston. Since it is weighted, the pressure produced is lost in pushing the piston upwards?

[alpha2cen]

So, the black one is the piston. Since it is weighted, the pressure produced is lost in pushing the piston upwards?

No, the pressure is always constant. The piston has no friction. The initial pressure is the sum of mg/A and atmospheric pressure.

where, m is mass, g is gravitational constant and A is area. There is no reason to be changed the pressure during the process.