Ideal gas undergoes cycle process

b_andries · Mar 28, 2011

Hi,

An amount of ideal gas undergoes the folowing cycle process in the following graph:

P-T graph of a closed cycle for an ideal gas: pressure p on the vertical axis (marks 12, 24, 36) against temperature T in K on the horizontal axis (marks 400, 800, 1200), with arrows showing the direction of the process.

This process can be presented by the following PV-graph :

Two P-V diagrams with axes p and V from origin O: the upper one shows a closed rectangle, the lower one shows a quadrilateral with dashed lines back to the origin, and a small loop labelled O between them.

The answer has to be the upper graph but why can't it be the lower graph ?
Thank you!

I like Serena · Mar 28, 2011

An ideal gas has: p V = n R T

That is: V = n R T / p

As you can see in the upper graph there are linear relations between T and p, meaning V must be constant, resulting in vertical lines in the p-V-graph.
Note that the diagonal lines in the upper graph can be extended to intersect the axes at the origin.

Ideal gas undergoes cycle process

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