How do I calculate the Gibbs free energy change for a reaction when given the entropy change, enthalpy change and the reaction conditions>

deltaG= Gibbs free energy 

deltaG=deltaH - TdeltaS 

If deltaH= 150 kJ/mol and deltaS=2.1 J/mol we must first convert the deltaS into kJ/mol, this is done by multiplying by 10^-3 .

So deltaS= 2.1 x 10^-3 kJ/mol. If the reaction is done at 25 degrees celcius, we must convert it to Kelvin, by adding 273. This gives 298 K. 

 

So the value of deltaG can be worked out:

 

deltaG= (150 kJ/mol) - (298) x( 2.1x 10^-3) 

deltaG= 149. 4 kJ/mol