Elemental carbon usually exists in one of two forms: graphite or diamond. It is

Question

Elemental carbon usually exists in one of two forms: graphite or diamond. It is generally believed that diamonds last forever. The table shows the standard enthalpy of formation (Hf) and the standard molar entropy (S) values for diamond and graphite. Substance Hf (kJ/mol) S (J/molK) Cgraphite 0 5.740 Cdiamond 1.897 2.38 Part A What is the standard Gibbs free energy for the transformation of diamond to graphite at 298 K? CdiamondCgraphite Express your answer to three significant figures and include the appropriate units.

Explanation / Answer

The expression for standard Gibbs free energy is

delta Grxn = delta Hrxn - (T x delta Srxn)

=1 mol x ( (0-1.897 kJ/mol ) - ( 298 K x (5.740 J/mol K - 2.38 J/mol K ) )

= -1.897 kJ - 1001.28 J

=-1.897 kJ - 1.00128 kJ

= - 2.90 kJ

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