## Example 8.5 in Textbook

$\Delta U=q+w$

Sonam Sidhu 2J
Posts: 14
Joined: Wed Sep 21, 2016 2:57 pm

### Example 8.5 in Textbook

"CALCULATING THE WORK, HEAT, AND CHANGE IN INTERNAL ENERGY FOR THE EXPANSION OF AN IDEAL GAS

Engineers working to develop new piston engines and turbines need to be familiar with the work and heat that are involved in various compression and expansion cycles that they use to model new engines.
Suppose that 1.00 mol of ideal gas molecules at an initial pressure of 3.00 atm is maintained at 292 K as it expands from 8.00 L to 20.00 L and a final pressure of 1.20 atm by two different paths. (a) Path A is an isothermal, reversible expansion. (b) Path B, a hypothetical alternative to path A, has two steps. In step 1, the gas is cooled at a constant volume until its pressure has fallen to 1.20 atm. In step 2, it is heated and allowed to expand against a constant pressure of 1.20 atm until its volume is 20.00 L and T = 292 K. Determine for each path the work done, the heat transferred and the change in internal energy (w, q, U')."

My question is how do we know that the change in internal energy is equal to 0?

Aishwarya_Natarajan_2F
Posts: 11
Joined: Mon Jul 11, 2016 3:00 am

### Re: Example 8.5 in Textbook

The change in internal energy is equal to 0 because we are told that the gas is an ideal gas.

When an ideal gas expands isothermally, the change in internal energy is equal to 0.