## 4F.17

$\Delta S = \frac{q_{rev}}{T}$

Alicia Lin 2F
Posts: 83
Joined: Wed Sep 18, 2019 12:17 am

### 4F.17

Calculate the standard entropy of vaporization of ammonia at 210.0 K, given that the molar heat capacities at constant pressure of liquid ammonia and ammonia vapor are 80.8J⋅K-1⋅mol-1 and 35.1J⋅K-1⋅mol-1, respectively, in this range (see Table 4C.1).

Can anyone give me guidance on how to start this problem? I'm not really understanding how entropy and heat capacity is related.

Nathan Nakaguchi 1G
Posts: 102
Joined: Wed Sep 18, 2019 12:22 am
Been upvoted: 1 time

### Re: 4F.17

Recall that S= Cln(T2/T1) so that's where heat capacities comes into play.

Additionally since S= q/T then S= deltaHvap/T

Those will be the formulas you will use for this question. Also, I think you have misread the question, you're reading 4F.18, 4F.17 uses water (however they both are the same process to solve so if you can do one you can do the other).

To solve this you have to use the fact that S is a state function so:

deltaS(total) = deltaS(heat liquid to boiling point) + deltaS(vaporization) + deltaS (bringing vapor to desired temperature)

Hope this helps!