Question

4. Thermodynamic data for C_(graphite) ​and C(^​_​diamond)​ at 298 K is given in the table below.

	delta Hf​o ​(kJ/mol)	o​ (J/mol K
C​(graphite)	0.0	5.740
C​(diamond)	1.895	2.377

a) Calculate delta H^​o​ and delta S^​o and delta G^​o ​for the transformation of 1 mole of graphite to diamond at 298 K.

b) Is there a tempature at which this transformation will occur spontaneously at atmospheric pressure? Justify your answer.

8. Methanol can be made using the Fischer-Tropsch process according to the reaction CO (g) + 2 H₂​ (g) <----> CH₃OH (g).

a) Calculate the entropy change for the reaction at 25^o.

b) Calculate the value of the equilibrium constant K at 25^o C.

c) What is the equilibrium partial pressure of methonal (CH₃​OH (g)) in the above reaction, if the inital partial pressures are P_CO ​= 1 atm and P_​(CH3OH) ​= 0.5 atm?

Answer 1

4)

a)
ΔHo = ΔHfo C(diamond) - ΔHfo C(graphite)
= 1.895 -0
= 1.895 KJ/mol
= 1995 J/mol

ΔSo = ΔSfo C(diamond) - ΔSfo C(graphite)
= 2.377 -5.740
= -3.363 J/mol-K

ΔGo = ΔHo - T*ΔSo
= 1995 - 298*(-3.363)
= 2997 J/mol
= 2.997 KJ/mol

b)
ΔGo = ΔHo - T*ΔSo
for reaction to be spontaneous,
ΔGo < 0
SO,
ΔHo - T*ΔSo < 0
1995 - T*(-3.363) <0
1995 + 3.363*T <0
for this to happen T must be negative
so it is not possible

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