how do you calculate delta G

afcwestwarrior

do i have to use this formula Delta G=delta h- t*delta s

or could i calculate it like i calculate delta h, products - reactants

pixel01

I think you can do either way. Which way is depending on what data you've got in hand

mrjeffy321

Calculating the change in the Gibbs Free Energy as,
ΔG = ΔH – T * ΔS
Is a more general way to do it since this will be true for any specified temperature, T.

You could calculate it as,
ΔG = G_products – G_reactants
But this will only be valid for the temperature which your table has its G values calculated in. You might have access to a table of standard G of formation, but this would only be true under standard conditions.
What if you had a non-spontaneous reaction (under standard conditions) and you wanted to find out the temperature you needed to raise it to in order to make it spontaneous? To do this, you would have to calculate it the old fashion way without the Free Energy table.