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**[SOLVED] Internal Energy of an ideal gas**

## Homework Statement

The temperature of 0.158 mol of an ideal gas is held constant at 67.0 degrees Celsius while its volume is reduced to a fraction of 20.0 % of its initial volume. The initial pressure of the gas is 1.19 atm.

What is the change in its internal energy?

## Homework Equations

[tex] U = \frac{1}{2}nRT [/tex] (Per degrees of Freedom)

## The Attempt at a Solution

I tried putting in the values to get U, but it doesn't say how many deggress of Freedom, so I triued using three (Monatomic) But this is wrong. Is there another Formula for the Internal Energy, becasue there are several similar questions, but none seem to be used with the

**releveant formula**above?

So any help/idea will be very greatly appreciated,

TFM