Free energy changes in metabolic reactions

[Hudson]

Hello Biologists!
I'm stuck on another question. I find the wording to be tricky. I think I'm kind of on the right path, but i definitely need some guidance.

the delta G of the following reaction is -2.8kcal/mol acetyl phosphate + ADP <--- ---> acetate + ATP.

Is the free energy difference per molecule of acetyl phosphate, relative to that of acetate, greater then, less then, or equal to that of ATP relative to its dephosphorylated counterpart?

So first, I dont know what a dephoshorylated counterpart means? I hope that doesnt sound silly, but does it mean the phosphate before it entered the rxn?
Second, I thought that when ATP changed to ADP, you have to add a H20. But since this reaction goes from ADP to ATP i'm not sure what equation to use. I'm all mixed up and I've read my pages over and over and I dont seem to get it. Can anyone help!

THanks for viewing xo

[Hudson]

i think i have to use ATP + H20 ---> ADP + Pi. But I'm not even sure. ANd i'm a little confused how to plug the numbers into that.

[JackBean]

the unphosphorylated counterpart is the one from pair missing phosphate. So from acetate/acetylphosphate it's acetate and from ADP/ATP it's ADP (yeah, it has 2 Pi, but lacks the gama-phosphate.
The water should be released, but in this case it's used to form the acetate

[Hudson]

so where do i incorporate the -2.8kcal. How do i tell what the free energy is doing?

[JackBean]

well, the free energy is used to phosphorylate ADP and rest is released as heat

[jungo60]

I believe H2O would be a bi-product of the hydrolysis from ATP to ADP.