Finding the energy of a system using the partition function

[dacruick]

Homework Statement

In part a) to this question I calculated the partition function which is Z = 1 + 3/e + 5/e^2

Homework Equations

I can't find an equation relating U to Z.

The Attempt at a Solution

If someone has an explanation or a link to an equation that would be great. Thanks.

 

[zhermes]

What's your situation, what type of particles are you considering?

 

[dacruick]

it does not specify but we deal mostly with ideal gases.

 

[vela]

Wikipedia has a brief summary.

http://en.wikipedia.org/wiki/Partition_function_(statistical_mechanics )