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## Homework Statement

There is a pressure volume graph with the gas changes shown, forming a rectangle. The corners are labled A to D starting from the upper left corner heading on to the right until it returns to point A again.

The question is at what point, or line is the internal energy of the gas greatest?

Like this, except the numbers are different.

## Homework Equations

ΔU = Q-W

## The Attempt at a Solution

**The prior question asked to find the temperatures at each point provided A was at 300K.**

So I thought that the internal energy of the gas would be maximum when it's at low volume and high pressure, therefore at point A. But at B & C it is hotter meaning it must have gained energy from an external source. So going to B it has expanded and gained energy. But by expanding it does work loosing internal energy right? So how come its temperature got higher? Honestly these graphs just confuse me a lot, I'd really appreciate any help.

So I thought that the internal energy of the gas would be maximum when it's at low volume and high pressure, therefore at point A. But at B & C it is hotter meaning it must have gained energy from an external source. So going to B it has expanded and gained energy. But by expanding it does work loosing internal energy right? So how come its temperature got higher? Honestly these graphs just confuse me a lot, I'd really appreciate any help.

**Thanks is advance:)**