Can I calculate dG with dH and without dS?

In almost all cases no. Reactions contribute to a change in entropy.

The combination of /_\H and -T/_\S must be NEGATIVE, indicating a release of total free energy.

 

Thus:

 

/_\G = /_\H - T/_\S

ok, something new to me, so sorry if i look a little stupid. What is gibbs equation?

put quite simply is a calculation of energies used or given during a chemical reaction

Yes predicting the Spontaneity of a Reaction.

in which way exactly, don't u use bond energies for this?

If Delta H were negative that would mean that the chemical system would lose energy to the surroundings and that should make the products more stable. /_\ represents the total energy exchange that takes place between the system and its environment and T/_\ represents the energy eused to take care of the intermolecular activity.

Isn't this just a calculation for making sure whether a reacton is exothermic or endothermic?

Pretty much, and energy consumption.

think Endothermic and Exothermic reactions, Gibbs is all rellated to that as well as the initial "trigger energies" for the reaction to take place, Gibbs is the "Maths Bit"

So, it works with both, the activation energies AND the energies that are involved in the reactions?

yup! that`s about it

 

sorry for repeating same info as Wolfson, he must type faster than me (not hard to do today, I`m in alot of pain with my hands)

Wolfson, probably knows alot more about the maths and calc side than myself, he`s worth listening to!

lol. Thanx alot!

Yes we can useit without the use of dH.

If we know the E(cell) then we can use the relation

Delta G= - nFE(cell)

I hope that relation can be used here

thanks.

 

hope dS wasn't given to me on the exam then.

dS = C ln (T2 / T1)

 

C = heat capacity.

 

then,

 

dG = dH - T dS

 

so i got it wrong on the test.