Here is a problem from Kaplan:
At 25 degrees C, the delta G naught for a certain reaction A < - -> B + 2C is 0. If the concentration of A, B, and C in the cell at 25 degrees C are all 10 mM, how does the delta G compare to the measurement taken at 1 M concentrations?
A. Delta G is greater than delta G naught, thus the reaction is spontaneous
B. Delta G is less than delta G naught, thus the reaction is spontaneous
C. Delta G is greater than delta G naught, thus the reaction is nonspontaneous
D. Delta G is less than delta G naught, thus the reaction is nonspontaneous
The answer is B and you can plug in the numbers into the equation, delta G = delta G naught + RT lnQ to get a negative delta G, which means it's spontaneous.
My question is two parts:
Part 1) from a conceptual perspective, why is delta G negative? If I change the concentration of both the reactants and products by the same amount shouldn't the reaction favor the products, since there is more products than reactants (3 products, which are B and 2C versus 1 reactant, A). I understand that this would be true for Keq<Q, which does not apply here, since we aren't given Keq (i.e. you don't know where equilibrium is). It might be helpful to see how someone goes through this problem conceptually without any equation and plugging in numbers.
Part 2) How do we account for the change in delta G if we were to use 20 M (a non-decimal number) instead of 10 mM?
At 25 degrees C, the delta G naught for a certain reaction A < - -> B + 2C is 0. If the concentration of A, B, and C in the cell at 25 degrees C are all 10 mM, how does the delta G compare to the measurement taken at 1 M concentrations?
A. Delta G is greater than delta G naught, thus the reaction is spontaneous
B. Delta G is less than delta G naught, thus the reaction is spontaneous
C. Delta G is greater than delta G naught, thus the reaction is nonspontaneous
D. Delta G is less than delta G naught, thus the reaction is nonspontaneous
The answer is B and you can plug in the numbers into the equation, delta G = delta G naught + RT lnQ to get a negative delta G, which means it's spontaneous.
My question is two parts:
Part 1) from a conceptual perspective, why is delta G negative? If I change the concentration of both the reactants and products by the same amount shouldn't the reaction favor the products, since there is more products than reactants (3 products, which are B and 2C versus 1 reactant, A). I understand that this would be true for Keq<Q, which does not apply here, since we aren't given Keq (i.e. you don't know where equilibrium is). It might be helpful to see how someone goes through this problem conceptually without any equation and plugging in numbers.
Part 2) How do we account for the change in delta G if we were to use 20 M (a non-decimal number) instead of 10 mM?