Question

For the reaction given below, the standard change in free energy has a positive value.

A+B<-->C+D

Changing the conditions of the reaction can alter the value of the change in free energy (?G). Sort the following conditions as to whether each would decrease the free energy value, increase the free energy value, or not change the free energy value for the reaction. For each change, assume that the other variables are kept constant.

a. Adding a catalyst

decrease the free energy value, increase the free energy value, or not change the free energy

b. increasing [C] and [D]

decrease the free energy value, increase the free energy value, or not change the free energy

c. Coupling with ATP hydrolysis

decrease the free energy value, increase the free energy value, or not change the free energy

d.Increasing [A] and [B]

decrease the free energy value, increase the free energy value, or not change the free energy

Answer 1

Concepts and reason

Standard change in free energy is an energy difference of standard free energy of products to thestandard free energy of reactants. Standard change in free energy is an energy, which explains about the spontaneity of the reaction.

Standard change in free energy has positive value, that indicates it is anendergonic reaction, and anegative value means exergonic reaction.

Fundamentals

Standard change in free energy:

Part a

Given equilibrium reaction

Equilibrium constant in terms of concentration is

If we add, catalyst to this reaction also remains same, which means that there is no change in equilibrium constant by the addition of catalyst.

That is there is no change in the free energy by adding the catalyst to the equilibrium reaction.

Part b

Equilibrium constant in terms of concentration is

If we increase the concentration of products, that is, theconcentration of C and concentration of D, Equilibrium constant () increases.

Therefore, the free energy increases by increasing the concentrations of products.

Part c

Given equilibrium reaction

Given that the standard change in free energy has a positive value it means that the reaction is anendergonic reaction.

ATP hydrolysis is an exergonic reaction which means energetically favourable reaction having the standard free energy value less than zero [negative value].

Therefore, by coupling this equilibrium, the reaction with ATP hydrolysis free energy decreases.

Part d

Equilibrium constant in terms of concentration is

If we increase the concentration of reactants, that is, concentration of A and concentration of B, equilibrium constant () decreases.

Therefore, the free energy decreases by increasing the concentrations of reactants.

Ans: Part a

No change in free energy

Part b

Increases the free energy value

Part c

Decreases the free energy value

Part d

Decreases the free energy value