Quiz 1 prep #9

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Quiz 1 prep #9

Postby Angela_Kim_1N » Mon Jan 30, 2017 12:57 pm

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
-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!

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Re: Quiz 1 prep #9

Postby Rishi_Kayathi_1E » Mon Jan 30, 2017 2:38 pm

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.

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Re: Quiz 1 prep #9

Postby NinaSheridan » Fri Feb 03, 2017 5:28 am

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.

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