Question 1

Which of the following statements correctly distinguishes between thermodynamics and kinetics in chemical reactions?

Accepted Answer

Thermodynamics determines the extent to which a reaction proceeds, while kinetics determines the rate at which a reaction occurs.

Question 2

In a reaction coordinate diagram, what does the highest point along the curve represent?

Accepted Answer

The transition state of the reaction

Question 3

Which of the following is true regarding the effect of enzymes on chemical reactions?

Accepted Answer

Enzymes lower the activation energy and increase the rate of both forward and reverse reactions.

Question 4

Given the rate constant equation $$k = \frac{k_B T}{h} e$$^{-\Delta G^{\ddagger}$$/RT}$$, which variable does an enzyme primarily affect to increase reaction rate?

Accepted Answer

The activation free energy $$\Delta G$$^{\ddagger}$$

Question 5

A reaction has a large negative $$\Delta G^\circ$$, but proceeds extremely slowly under standard conditions. What does this indicate?

Accepted Answer

The reaction is thermodynamically favorable but has a high activation energy barrier.

Question 6

Which of the following best describes the role of binding energy in enzyme catalysis?

Accepted Answer

Binding energy lowers the activation energy by stabilizing the transition state.

Question 7

Consider the Haber-Bosch process for nitrogen fixation: $$N_2 + 3H_2$$ \rightarrow 2NH_3$$ with $$\Delta G^\circ = -33.5$$ kJ/mol. Why is this reaction slow without a catalyst?

Accepted Answer

The activation energy for breaking the $$N \equiv N$$ triple bond is very high.

Question 8

Which of the following is NOT a property of enzyme active sites?

Accepted Answer

They always contain water to facilitate substrate binding.

Question 9

If an enzyme increases the rate of a reaction by a factor of $$10^8 at 25$$°C, what is the approximate decrease in activation free energy $$\Delta \Delta G$$^{\ddagger}$$? (Use R = 8.314$ J/mol·K, T = 298$ K)

Accepted Answer

$$\Delta \Delta G$$^{\ddagger}$$ \approx -45 kJ/$$mol

Question 10

Which of the following scenarios would NOT increase the rate of a chemical reaction?

Accepted Answer

Increasing the activation energy

Question 11

The equilibrium constant $$K_{eq}$$ for a reaction is related to the standard free energy change $$\Delta G^\circ by $$which equation?

Accepted Answer

$$\Delta G^\circ = -RT \ln K_{eq}$$

Question 12

Which of the following is true about the rate-limiting step in an enzyme-catalyzed reaction?

Accepted Answer

It determines the overall rate of the reaction.

Question 13

Suppose an enzyme forms three hydrogen bonds with its substrate, each contributing $$-20 kJ/$$mol to binding energy. What is the expected rate enhancement at 25°C ($$T = 298 K$$)?

Accepted Answer

$$e^{(60,000)/(8.314 	imes 298)}$$ \approx 1.1 	imes $$10^{11}$$

Question 14

Which of the following is a consequence of enzyme specificity?

Accepted Answer

Enzymes only bind substrates with complementary shape and chemical groups.

Question 15

Why do enzymes not affect the final equilibrium position of a reaction?

Accepted Answer

Because they lower activation energy for both forward and reverse reactions equally.

Question 16

Which of the following is a correct statement about the relationship between the forward and reverse rate constants and the equilibrium constant?

Accepted Answer

$$K_{eq} = \frac{k_{forward}}{k_{reverse}}$$

Question 17

Which of the following is NOT a way enzymes achieve rate enhancement?

Accepted Answer

Changing the overall free energy difference between reactants and products

Question 18

A protease enzyme cuts only at specific peptide bonds due to which property?

Accepted Answer

Its steric and chemical complementarity to the substrate

Question 19

Which of the following is a correct interpretation of the equation $$k = \frac{k_B T}{h} e$$^{-\Delta G^{\ddagger}$$/RT}$$?

Accepted Answer

The rate constant $$k$$ decreases as $$\Delta G$$^{\ddagger}$$ increases.

Enzymes I: Introduction to Enzymes – Thermodynamics and Kinetics

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