## 9.13

Volume: $\Delta S = nR\ln \frac{V_{2}}{V_{1}}$
Temperature: $\Delta S = nC\ln \frac{T_{2}}{T_{1}}$

Abigail Urbina 1K
Posts: 102
Joined: Thu Jul 27, 2017 3:01 am

### 9.13

Whenever a question states that we should assume ideal gas behavior, are we always supposed to plug in 1.00 mol of gas into an equation when the amount of moles is not given? Are there certain circumstances (other than when they actually give us the amount in moles of gas) where we should not automatically utilize 1.00 mol in our calculations?

Sabrina Dunbar 1I
Posts: 57
Joined: Fri Sep 29, 2017 7:07 am
Been upvoted: 1 time

### Re: 9.13

For this question in particular, you are given all of the information necessary to calculate the number of moles using the ideal gas law, PV=nRT. n turns out to not be 1.00 mol, so here the solution would be incorrect if 1.00 mol was assumed to be the value of n. I think a general rule would be that if you have enough information to solve for n any other way, then use that operation. Assuming 1.00 may be necessary in some calculations, but in 9.13 it is not because you are given enough information to find it on your own. Hopefully this helps!

Amy Zheng 2l
Posts: 57
Joined: Fri Sep 29, 2017 7:04 am

### Re: 9.13

In the solution manual it said to assume ideal behavior and 1 mol of N2 gas

Payton Schwesinger 1J
Posts: 45
Joined: Fri Sep 29, 2017 7:04 am

### Re: 9.13

You need to have a value in moles so that the units will cancel-- multiplying "n (mol)" times "R (J/ mol K) allows the moles to cancel so you get the correct units. If it is given, you use that, but sometimes you must solve for "n" using the ideal gas law.