Chem question

[kuma]

Advertisement - Members don't see this ad

I don't completely understand PV work and how it relates to when you change a bolume of a gas at constant P. So at const P any change in V is work, when you decrease the gas at constant P you will be doing work on the gas and thus increasing its heat? or its Temp or its KE? (Kinetic Engergy)
How do you keep this system at constant P, if you are changing the Volume?
Thanks

 

[researchprof]

I don't completely understand PV work and how it relates to when you change a bolume of a gas at constant P. So at const P any change in V is work, when you decrease the gas at constant P you will be doing work on the gas and thus increasing its heat? or its Temp or its KE? (Kinetic Engergy)
How do you keep this system at constant P, if you are changing the Volume?
Thanks

PV=nRT so P/nR = T/V. so you proportionally vary T and V to get constant P.

The same thing applies to the PdV = dW relation.

 

[inshanesworld]

Yes and the other thing to remember is that the P in Pdv is P external thus if I have a gas in a cylinder and there is a piston in the system. The piston exerts a force on the gas that reduces the volume of the gas in that cylinder...then the piston has done work on that gas that is equal to the pressure applied by the cylinder times the change in volume of the gas. If the piston then is released such that the net force on the gas allows it to expand and raise the piston then the gas has done work equal once again to P external times the change in volume. IT IS NOT THE PRESSURE OF THE GAS WHEN THE SYSTEM CONSISTS AS I HAVE JUST EXPLAINED.