Hydrolysis of Acetyl phosphate

[Jacob Afable 3J]

Winter 2013 Q2B:

Why do we divide the hydrolysis of ATP by the formation of acetyl phosphate to get the amount of moles of ATP?

[Irena Roy 4H]

The question is essentially asking: How many moles of ATP do you need to hydrolyze in order to get the amount of energy needed to phosphorylate 1 mole of acetyl phosphate?

In this case, the hydrolysis of 1 mole of ATP releases -30.5 kJ in energy.
The hydrolysis of acetyl phosphate is -41 kJ/mol. The phosphorylation of acetic acid is the reverse of this process, for a value of 41 kJ/mol.
1 mole of acetyl phosphate molecules are formed during the phosphorylation of acetic acid. So (41 kJ/mol)(1mol) = 41 kJ.
41 kJ is the amount of energy involved when 1 mole of acetyl phosphate molecules are formed.

So the question is, how many moles of ATP do I need to hydrolyze in order to get 41 kJ?

We know that 1 mole of ATP releases -30.5 kJ aka -30.5 kJ/mol ATP. At this point this is just basic stoichiometry, so: 41 kJ = (30.5 kJ/mol)(x)
Solve for x to get the number of moles of ATP you need to hydrolyze. This should be 1.3 moles of ATP. For part b of this question, use a similar process.