The standard state Gibb's free energies of formation of C (graphite) and C (diamond) at T = 298   K…

The standard state Gibb's free energies of formation of  C (graphite) and C (diamond) at T=298 K are
ΔfGoC (graphite=0 kJ mol-1
ΔfGoC diamond=2.9 kJ mol-1
The standard state means that the pressure should be 1 bar, and substance should be pure at a given temperature. The conversion of graphite [C (graphite)] to diamond [C (diamond)] reduces its volume by 2×10-6 m3 mol-1 . If C (graphite) is converted to C (diamond) isothermally at T=298 K, the pressure at which C (graphite) is in equilibrium with C (diamond), is
[Useful information: 1 J=1 kg m2 s-2, 1 Pa=1 kg m-1s-2; 1bar=105Pa]
  1. 14501 bar
  2. 29001 bar
  3. 58001 bar
  4. 1450 bar

Solution

CgraphiteCdiamond; ΔGo=ΔfGdiamondo-ΔfGgraphiteo=2.9 kJ/mol  at 1 bar

As dGT=V.dP

ΔG1ΔG2dΔGT= P1P2ΔV.dP

ΔG2-ΔG1=ΔV. P2-P1

2.9×103-0=-2×10-6 1-P2

P2-1=2.9×1032×10-6Pa=1.45×104 bar

P2=14501  bar.

Asked in: JEE Advanced 2017 (Paper 2)

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