Module 1: V1 - V4

Question 1

What is Gibbs Free Energy?

Answer 1

the energy of the reaction available to do work

Question 2

What is the equation for Gibbs Free Energy?

Answer 2

ΔG = ΔH - TΔS

Question 3

What are the characteristics of an exergonic reaction?

Answer 3

ΔG is negative, free energy released, favourable, spontaneous

Question 4

What are the characteristics of an endergonic reaction?

Answer 4

ΔG is positive, free energy absorbed, unfavourable, not spontaneous

Question 5

What does K the thermodynamic equilibrium constant for the reaction describe?

Answer 5

the “position” of the reaction at equilibrium i.e. the relative concentrations of components at equilibrium

Question 6

What is the difference between ΔG and ΔG˚?

Answer 6

ΔG is the actual free energy change for the reaction, while ΔG˚ is how much work the reaction can do, starting from standard conditions

Question 7

What are the standard conditions for biochemistry?

Answer 7

• 298 K
• 101.3 kPa (1 atm)
• reaction occurs in a well buffered solution at pH 7
• [H+] = 10^-7 (neutral pH)
• Mg2+ = 1mM (required as a cofactor for enzymes)

Question 8

What happens to the equation when concentration of all products and reactants in the system is = 1?

Answer 8

ΔG = ΔG˚ + RTIn[1][1]/([1][1])
ΔG = ΔG˚ - RTIn(1)
ΔG = ΔG˚

Question 9

What happens to the equation when the reaction is at equilibrium?

Answer 9

the reaction can do no more work, therefore:
ΔG = ΔG˚ + RTIn[C][D]/([A][B])
0 = ΔG˚ + RTIn[C][D]/([A][B])
ΔG˚ = -RTInK

Question 10

What is the ‘driving force’ of a reaction?

Answer 10

the chemical potential difference between products and reactants

Question 11

What is the position of a reaction at equilibrium?

Answer 11

the point in a chemical reaction at which the concentration of reactants and products are no longer changing

Question 12

Under a given set of conditions, what determines how much work a reaction can do?

Answer 12

ΔG

Question 13

Under what initial conditions will a reaction occur spontaneously?

Answer 13

under initial conditions in which there are much more reactants than products

Question 14

Describe the three ways an ‘unfavourable’ reaction can be made favourable.

Answer 14

1) remove one or more of the products at a rate much faster than it is produced so that the reaction is “kinetically” driven
2) replenish one or more of the reactants at a rate much faster than it is removed so that the reaction is “kinetically” driven
3) couple the “unfavourable” reaction with a highly “favourable” reaction e.g. 13.8 - 30.5 = -16.7 kJ/mol = spontaneous

Question 15

Is energy required or released when a bond is broken?

Answer 15

energy is required

Question 16

Is energy required or released when a bond forms?

Answer 16

energy is released

Question 17

Why does hydrolysis of ATP yield energy? List the reasons.

Answer 17

ATP has a higher negative charge density than ADP (less stable)
Pi is very stable: multiple resonance states exist
ATP phosphoanhydride bonds are relatively weak
ADP phosphoanhydride bonds and Pi bonds are relatively strong

Question 18

Does a positive change or a negative change in free energy indicate a favourable reaction?

Answer 18

a negative change in free energy indicates a favourable reaction

Question 19

How is the free energy change of the reverse reaction related to that of the forward reaction?

Answer 19

the change in free energy is the difference between heat released during a process and the heat released for the same process occurring in a reversible manner

Question 20

If some spontaneous event is endothermic, what must have been the “driving force” behind that event, enthalpy or entropy?

Answer 20

entropy

Question 21

If a reaction has a positiveΔG′⁰ it is often described as ‘unfavourable’. What is wrong with this statement?

Answer 21

this is wrong because the value for RTIn[C][D]/([A][B]) can be significantly negative if there is a larger proportion of reactants in comparison to products and this will result in a favourable reaction as it will outweigh the positive ΔG′⁰ value