Gibbs free energy is a measure of the spontaneity of a chemical reaction. It is
ID: 852622 • Letter: G
Question
Gibbs free energy is a measure of the spontaneity of a chemical reaction. It is the chemical potential for a reaction, which is minimized at equilibrium. It is defined as
G=H?TS
Elemental carbon usually exists in one of two forms: graphite or diamond. It is generally believed that diamonds last forever. Here are the standard enthalpy of formation (?H?f) and the standard molar entropy (S?) values for diamond and graphite.
Part A
Cdiamond?Cgraphite
Express your answer to three significant figures and include the appropriate units.
Gibbs free energy is a measure of the spontaneity of a chemical reaction. It is the chemical potential for a reaction, which is minimized at equilibrium. It is defined as
G=H?TS
Elemental carbon usually exists in one of two forms: graphite or diamond. It is generally believed that diamonds last forever. Here are the standard enthalpy of formation (?H?f) and the standard molar entropy (S?) values for diamond and graphite.
Substance ?H?f (kJ/mol) S? (J/mol?K) Cgraphite 0 5.740 Cdiamond 1.897 2.38Part A
What is the standard Gibbs free energy for the transformation of diamond to graphite at 298 K?Cdiamond?Cgraphite
Express your answer to three significant figures and include the appropriate units.
Explanation / Answer
Delta H = Enthalpy sum of products - enthalpy sum of reactants. So in this case, it would be:
0 - 1.897 = -1.897 kJ/Mol. (delta H)
Now we have to calculate the Delta S which is the entropy sum.
5.740-2.38 = 3.36 J/mol (delta S)
Take a second look at the units - they are in "j/Mol" whereas the enthalpy is given in "kJ/mol." Our final answer is going to be in kJ, so it would make sense to convert our answer to kJ.
3.36 J/mol = 0.00336 kJ/mol.
We are given the temperature in Kelvin which fits this equation so no further conversions have to be completed. Now we can plug our answers into the equation...
-1.897-(298 x 0.00336)
and we get our final answer of -2.90 kJ.
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