Question

When will a chemical reaction proceed spontaneously in the forward direction (substrate -> products) in a cell?

1. ΔG°’ > 0
2. ΔG°’ < 0
3. ΔG > 0
4. ΔG < 0

A large change in the equilibrium constant K’eq is associated with a __________ change in ΔG°’.

1. Relatively small
2. Relatively large

What does ΔG°’ tell you about a given chemical reaction?

1. Whether or not the reaction will proceed spontaneously in the forward direction in a cell.
2. Which direction and how far a reaction must go to reach equilibrium under standard conditions.
3. The amount of ATP hydrolysis required for the reaction to proceed spontaneously.
4. The concentration of products and reactants in a cell.

Answer 1

Answer 1. (D) ΔG < 0

ΔG negative, the reaction proceeds spontaneously with the loss of free energy (exothermic).

In all spontaneous biochemical reaction, the free energy of the reactive system ΔG is negative, but ΔG° may be positive, negative or zero depending upon the equilibrium constant of the reaction.

Answer 2. Relatively small

ΔG°' = -RT ln K​​​​​'eq

Answer 3. (B) which direction and how far a reaction must go to reach equalibrum under standard conditions.

The actual free energy change (ΔG) for any chemical reaction is a function of standard free energy change (ΔG°’) and a term that express the initial concentration of reactants and products. The actual change in free energy during a reaction is influenced by temperature, pressure and the initial concentration of reactants and products and usually differ from standard free energy change, ΔG°’.

The chemical reaction has a characteristic standard free energy change and it is constant for a given reaction. It can be calculated from the equalibrum constant of the reaction under standard conditions i.e. at a solute concentration of 1.0M, at temperature of 25o c and 1.0 ATM pressure. The free energy change with correspond to this standard state is known as standard free energy change.

ΔG°’ = -RT ln K'eq

This equation allows some simple predictions:

Keq >1 then ΔG°’ negative - reaction proceeds forward

Keq = 1 then ΔG°’ zero - is at equalibrum

Keq <1 then ΔG°’ positive - reaction proceeds in reverse