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Homework Help: Pressure above which graphite will spontaneously change into diamond

  1. Mar 15, 2009 #1
    1. The problem statement, all variables and given/known data

    Calculate the pressure at which graphite spontaneously changes to diamond.

    T = 298.15 K (isothermal)
    Vdiamond - Vgraphite = -2 x 10-6m3/mol

    At 273.15K and 1 bar (105 Pa):
    ΔGf graphite = 0
    ΔGf diamond = 2.9 kJ/mol
    i.e. graphite is the more stable and preferred form of carbon in the above conditions.

    2. Relevant equations

    Not really sure here... Could be anything.

    Perhaps useful is: G = H - TS

    But I don't see where P fits in.

    3. The attempt at a solution

    Well, I know G will be 0 at the pressure I am trying to identify (i.e. graphite and diamond will be in equilibrium, with equal tendency for the carbon to form either).
  2. jcsd
  3. Mar 16, 2009 #2


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    Science Advisor
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    G = H - TS is definitely relevant if you expand H by using its definition.
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