Using standard the thermodynamic properties shown below estimate the normal boiling point of carbon disulfide (CS2).

Question

Using standard the thermodynamic properties shown below estimate the normal boiling point of carbon disulfide (CS₂) in C.

	Molar Mass (g/mol)	ΔHof (kJ/mol)	So [J/(mol·K)]	ΔGof (kJ/mol)
CS2(g)	76.143	115.3	237.8	65.1
CS2(ℓ)	76.143	87.9	151.0	63.6

Answer 1

We are looking at the following reaction:

CS₂(l) <==> CS₂(g) ... phase transition from liquid to gas

At equilibrium (the boiling point), we have the following relationship:

∆Gº = ∆Hº - T∆Sº = 0

∆Hº - T∆Sº = 0

T = ∆Hº / ∆Sº (T is the thermodynamic boiling point)

Now, we only need to find ∆Hº and ∆Sº.

∆Hº_rxn = ∆H_formation products - ∆Hº_formation reactants = 115.3 - 87.9 = 27.4 kJ/mol

∆Sº_rxn = ∆Sº_products - ∆Sº_reactants = 237.8 - 151.0 = 86.8 J/mol = 0.0868 kJ/molK

Plugging these values in and solving for T, we have...

T = 27.4 kJ/mol / 0.0868 kJ/molK

T = 315.7K

T = 42.5ºC