Question

Use the Joback method to estimate the Tc and Pc of each of the following compounds:

A. Butane

B. 1- Hexanol

C. 2-chloropentance

D. 3-Hexane

E. 1,3 butadiene

Answer 1

To do this, I need the chart of relations for each group in the molecules. Honestly I don't have that, try to check your text book if you have it, and with them, you can have an idea of how to solve this. I manage to find some values, but not all of them, however, I'll do an example calculation for Butane, so you can have an idea.

First the Butane is CH3 - CH2 - CH2 - CH3. It has 2 CH3 and two CH2. To estimate the Tc and Pc by the joback method, you need to apply the following expression:

Pc = (0.113 + 0.0032na - E)^-2
Tc = Tb(0.584 + 0.965E - E²)^-1

Where na is the number of atoms and E is the sum of the contributions of individuals groups in the molecule. The Tb is also calculated by:
Tb = 198.2 + E

Now for this molecules, you need the chart for group activity method (You may find it in appendix of your text book). In the case for this molecule we have:

Group	#ocurrences	Tb	Tc	Pc
CH3	2	23.58 * 2	2 * 0.0141	2 * -0.0012
CH2	2	22.88 * 2	2 * 0.0189	0
E(sum)		92.92	0.066	-0.0024

Then, we use the above expressions:
Tb = 198.2 + 92.92 = 291.12 K

Tc = 291.12(0.584 + (0.965*0.066) - (0.066)²)^-1 = 452.52 K
Pc = (0.113 + 0.0032(14) - (-0.0024))^-2 = 38.96 bar

Applying the same procedure, you will solve the other molecules.

Hope this helps