## Standard residual entropy problem

Joanne Reyes 1L
Posts: 21
Joined: Fri Sep 25, 2015 3:00 am

### Standard residual entropy problem

This question says "Assume COF2 adopted disordered arrangements in its crystal form, what would its residual molar entropy be?" and the answer is W = 3NA, S = k ln 3 NA = R ln 3 = 9.1 J/K. How would I go about solving this problem? Thanks.

Jeannie Huang 3B
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

### Re: Standard residual entropy problem

To answer the question, you need to draw the lewis structure for COF2. You should get a trigonal planar shape with C in the center. You could get 3 different orientations of the molecule since the O can be in one of the three corners. Following the equation,

S = k ln W (refer to pg. 32 of course reader)
and since W = 3^(NA) for the three different orientations, and assuming 1 mole of COF2,

You get S = k x (avogadro's # x 1 mol) x ln(3) = R ln 3 = 9.1 J/K.

Hope this helps! (and someone verify that I've explained correctly).

Chem_Mod
Posts: 19178
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 833 times

### Re: Standard residual entropy problem

k = boltzmann constant is J/(particle*K)

NA= Avogadro's number = 6.022 x 1023 = particles/mole

k*NA= J/(mol*K) = R

If you're given a certain number of moles then

S=nRln(a) for the units to work out J/K, where a is the number of ways the molecule can be positioned (W=aNA)

Return to “Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)”

### Who is online

Users browsing this forum: No registered users and 1 guest