## Quiz 1 prep #9

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

$\Delta G^{\circ}= -RT\ln K$

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

Angela_Kim_1N
Posts: 21
Joined: Fri Jul 22, 2016 3:00 am

### Quiz 1 prep #9

A sample of 1 mol of gas initially at 1 atm and 298K is heated at constant pressure to 350K, then the gas is compressed isothermally to its initial volume and finally it is cooled to 298K at constant volume. Which of the following values is zero?
-Delta S of surrounding and Delta G
-Delta S of system and Delta S of surrounding
-q and w
-W
-Delta G and Delta S of system

The answer is Delta G and Delta S of system.

Can someone please walk me through the question?
Thank you!

Rishi_Kayathi_1E
Posts: 24
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Quiz 1 prep #9

Gibbs free energy and entropy of a system are both state function. As the process is a cyclic function, the system always returns to the same state. Hence, as it returns to the same state the change is 0 in the aforementioned properties.

NinaSheridan
Posts: 30
Joined: Wed Sep 21, 2016 2:58 pm

### Re: Quiz 1 prep #9

If you're still confused about why entropy of the system and entropy of the surroundings aren't both zero (why option A and B aren't correct if entropy in general is a state function), the situation with isothermal reversible reactions having a net change of zero while irreversible reactions have an entropy above zero makes the first two options incorrect.