Understanding Entropy: Drawing Temperature Entropy Graphs

[Delzac]

Homework Statement

Hi all,

Is there anyway, meaning by use of equation to determine how we should draw a temperature entropy graph?

I understand that is the equation for entropy for ideal gas transformation:

$$\del S = nC_vln(\frac{T_f}{T_i}) + nRln(\frac{V_f}{V_i})$$

But i don't seem to be able to apply it very well.

For example, in a adiabatic compression, the entropy doesn't change but temperature does (appears as straight line on graph). Yet, the equation tells me that there should be change in entropy. That is, if i understanding is not wrong.

So it there any generally guidelines to drawing the graph, and whether the curve is concave or convex.

 

[madmike159]

I’m not familiar with this, but if Cv was small and Rl was large then entropy wouldn't change (much) if T did. You are taking the natural log of T so a change would have little effect, and if the right side of the + was a large number then a small change on the left side of the + would not make much difference to entropy.

 

[Delzac]

How about, say a isobaric heating, how would one then determine the curvature of its temperature entropy curve?

Any help from anyone will be greatly appreciated.