Question

. In a biochemical reaction, A + B-->C with äG = 30 kJ/mol. Which of the following reactions might be effectively coupled to this reaction so that it becomes more spontaneous?

I. C + D are the reactants, and B + E are the products

äG = -40 kJ/mol


II. C + D are the reactants, and B + E are the products

äG = +40 kJ/mol

a.I only
b.II only
c.I or II
d.Neither I nor II can increase spontaneity.
e.No coupling is required as the reaction is already spontaneous.

Answer 1

Aren't I and II the same?

Answer 2

The only difference is the + and - for the dGrxn

Answer 3

Thank you for pointing out the obvious. I missed it.
I see it this way.
I. A+B==> C +30 (not spontaneous)
...C+D==> B+E -40
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B and C cancel and adding we get
A + D ==> E +30-40 = -10 (spontaneous)
Under the other one dGrxn = +70 kJ.
So I think I should help. II will not.

Answer 4

Thank you very much! That's what I got. I appreciate it.