In: Chemistry
Imagine that inside a cell the [creatine phosphate] = 3.5 mM, [creatine] = 0.6 mM, and [Pi] = 4.3 mM. Furthermore, imagine that the pH inside the cell is 7.4. Given that ΔG°′ for creatine phosphate hydrolysis is -10.3 kcal/mol, what is the ΔG for creatine phosphate hydrolysis inside the above-described cell, which is at 37 °C? Report your answer in kcal/mol to the nearest tenths. Hint: you might wish to consult the chapter in our text that discusses thermodynamics.
Reactions are classified as either exothermic (H < 0) or endothermic (H > 0) on the basis of whether they give off or absorb heat. Reactions can also be classified as exergonic (G < 0) or endergonic (G > 0) on the basis of whether the free energy of the system decreases or increases during the reaction.
When a reaction is favored by both enthalpy (Ho < 0) and entropy (So > 0), there is no need to calculate the value of Go to decide whether the reaction should proceed. The same can be said for reactions favored by neither enthalpy (Ho > 0) nor entropy (So < 0). Free energy calculations become important for reactions favored by only one of these factors.
The value of G at that moment in time will be equal to the standard-state free energy for this reaction, Go.
When Qp = 1: |
G = Go |
When a reaction leaves the standard state because of a change in the ratio of the concentrations of the products to the reactants, we have to describe the system in terms of non-standard-state free energies of reaction. The difference between Go and G for a reaction is important. There is only one value of Go for a reaction at a given temperature, but there are an infinite number of possible values of G.
therefore,ΔG for creatine phosphate hydrolysis inside the above-described cell is 10.3 kcal/mol