Relation among thermodynamic quantities The thermodynamic properties for a react

Question

Relation among thermodynamic quantities

The thermodynamic properties for a reaction are related by the equation that defines the standard free energy, ?G?, in kJ/mol:

?G?=?H??T?S?

where ?H? is the standard enthalpy change in kJ/mol and ?S? is the standard entropy change in J/(mol?K). A good approximation of the free energy change at other temperatures, ?GT, can also be obtained by utilizing this equation and assuming enthalpy (?H?) and entropy (?S?) change little with temperature.

Part A

For the reaction of oxygen and nitrogen to form nitric oxide, consider the following thermodynamic data:

Calculate the temperature in kelvins above which this reaction is spontaneous.

Explanation / Answer

DG = DH - TDS [Consider The 'D' as caps delta]

For a reaction to be spontaneous at a give temperature DG must be negative.

i.e. for spontaneity

DH < TDS

Or   T > DH/DS

T > (180.5kJmol-) /(24.80

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