# PV diagrams for ideal gas

1. Aug 22, 2014

### slaw155

1. The problem statement, all variables and given/known data
Imagine a graph of pressure in kPa (y-axis) against volume in L (x-axis). There is a straight line moving from point A at 300kPa, 0.5L to point B at 500kPa, 1L. The false origin on this graph is 200kPa, 0L. What is the work done by the gas?

2. Relevant equations

W=pV

3. The attempt at a solution
I know that work is area under graph so its basically the area of a triangle plus area of trapezium. But this gives work = 100J but textbook says 200J. Where have I gone wrong?

2. Aug 22, 2014

### ehild

See the picture . You need the blue area from the really zero pressure.

ehild

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• ###### PVW.JPG
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3. Aug 22, 2014

### Andrew Mason

Use the formula for area of a trapezoid: (L1 + L2)/2 x W

AM

Last edited: Aug 22, 2014
4. Aug 22, 2014

### ehild

You meant trapezoid, I think

ehild

5. Aug 22, 2014

### Andrew Mason

Right. A trapezoid.

AM