If pressure remains constant and volume changes, what is the work?

Question

W=PdV

What is the work if pressure changes and volume remains constant?

Answer 1

Work is defined as a force acting through a displacement. Essentially, if a weight can be raised through a distance, work has been performed. In your example, where the pressure changes but the volume remains constant, no work has been done because nothing in the system can be equated to raising (or lowering) a weight. The internal energy in the system has indeed changed, and that energy could be converted into work if the volume were allowed to change to relieve the change in pressure.

One of the previous answers was quite good except for blurring the lines between internal energy and work. You could look at it that the change in internal energy represents a change in the ABILITY to do work, but until that energy is converted into a force moving through a displacement, the energy remains INTERNAL to the system. It doesn't become work until it changes something outside the system.

Answer 2

If pressure remains constant and volume increases, the volume change must result in pushing something out of the way or work done.

If pressure changes and volume remains constant something is putting heat in or taking it out ( and maybe shaking it all about). You could claim that work is being done to speed up the gas molecules (or that they are doing work on the container by transferring kinetic energy in inelastic 'collisions') but for some reason people seem to prefer to refer to this as 'changing the internal energy'.

If pressure is constant and volume decreases then heat is flowing out of your container, as above you can either treat this as work being done or a change in internal energy - as far as I can tell it is a matter of convenience as the two terms seem interchangeable but what do I know? maybe there is a significant difference if you are not looking at a reversible cycle.

Best of Luck

Answer 3

The thing u are asking about is otto cycle on which most of the petrol engies work.However it is ideal and bit different than actual cycle.While the addition of heat ie injecting fuel in the cylinder, it is assumed that piston is stationary at top dead centre and so volume is constant and then fuelis added to it and pressure of cylinder rises and thus in this case pressure is changing but volume is constant.
If the area of the curve,(taking P on Y axis and V on X axis) is calculated then it gives work done by the engine.(becuase heat energy is being converted to work)

Answer 4

PV = NRT

If pressure is constant and volume changes, then the temperature must change, so work is incurred.

Answer 5

If the pressure goes up, the work increases. If the pressure goes down, the work decreases. You can see from the equation that they are directly proportional.

Answer 6

In this case, Work is synonymous with Temperature. Temperature varies directly with pressure and indirectly with volume

Answer 7

big explosion! or the opposite it depends on the pressure change if it is decreasing or increasing .....

Answer 8

Heat. +-