Question 1

Which of the following best describes a compound that is thermodynamically unstable but kinetically stable?

Accepted Answer

It has a high activation energy barrier but a negative $$\Delta G$$ for the reaction.

Question 2

Given the reaction: $$A \rightarrow B$$, where $$A is $$thermodynamically unstable relative to $$B$$, which of the following statements is correct?

Accepted Answer

$$\Delta G$$ for the reaction is negative, and the reaction is spontaneous under standard conditions.

Question 3

In the context of enzyme-catalyzed reactions, what does the rate-determining step (r.d.s.) correspond to on a reaction coordinate diagram?

Accepted Answer

The highest energy transition state along the reaction pathway.

Question 4

If a reaction coordinate diagram shows three peaks, with the second peak being the highest, which step is the rate-determining step?

Accepted Answer

The step associated with the second peak.

Question 5

A reaction has $$\Delta G = -40 kJ/$$mol. What does this indicate about the reaction?

Accepted Answer

The reaction is thermodynamically favorable and can proceed spontaneously.

Question 6

Which of the following best explains why ATP is considered thermodynamically unstable but kinetically stable in cells?

Accepted Answer

ATP hydrolysis has a large negative $$\Delta G$$, but the activation energy for hydrolysis is high without enzymes.

Question 7

If a substrate is thermodynamically stable but reacts very slowly, what can be inferred about its reaction coordinate diagram?

Accepted Answer

The activation energy ($$E_a) is $$high, but $$\Delta G is $$positive or near zero.

Question 8

Which of the following is true regarding the relationship between kinetic and thermodynamic stability?

Accepted Answer

A compound can be thermodynamically unstable but kinetically stable if the activation energy is high.

Question 9

Consider a reaction with multiple steps, each with its own activation energy. Which step determines the overall rate of the reaction?

Accepted Answer

The step with the highest activation energy barrier.

Question 10

A reaction coordinate diagram shows a substrate at a higher energy than the product, but the reaction does not proceed rapidly. What is the most likely explanation?

Accepted Answer

The activation energy barrier is high, making the reaction kinetically slow.

Question 11

If the $$\Delta G$$ for a reaction is calculated as follows: $$\Delta G = G_{products} - G_{reactants}$$, and $$G_{products} \u003c G_{reactants}$$, what can be concluded?

Accepted Answer

The reaction is exergonic and thermodynamically favorable.

Question 12

Which of the following best describes the effect of an enzyme on a reaction coordinate diagram?

Accepted Answer

It lowers the activation energy ($$E_a) $$but does not change $$\Delta G.$$

Question 13

A reaction proceeds through three transition states with the following activation energies: 20 kJ/mol, 50 kJ/mol, and 30 kJ/mol. Which is the rate-determining step?

Accepted Answer

The step with 50 kJ/mol activation energy.

Question 14

In a biological pathway, why might a thermodynamically favorable reaction not occur rapidly in the absence of an enzyme?

Accepted Answer

The activation energy barrier is too high for the reaction to proceed at a significant rate.

Question 15

Which of the following statements about the rate-determining step (r.d.s.) is correct?

Accepted Answer

It is the slowest step in a multi-step reaction and has the highest energy barrier.

Kinetic vs. Thermodynamic Stability and Reaction Coordinate Diagrams in Biochemistry

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