Question 1

Which of the following statements best describes the role of the transition state in a chemical reaction pathway?

Accepted Answer

The transition state is the highest energy point along the reaction coordinate, representing the point at which bonds are partially broken and formed.

Question 2

In the rotation around the $$\mathrm{C_2$-C_3$}$$ bond in butane versus 2-butene, which statement is correct regarding their activation energies ($$E_a$$)?

Accepted Answer

Rotation around the $$\mathrm{C_2$-C_3$}$$ bond in 2-butene has a much higher $$E_a$$ than in butane due to the presence of a double bond.

Question 3

Given the acid-base reaction: $$\mathrm{HO-H + ^-OCH_2CH_3 \rightarrow HO^- + HOCH_2CH_3}$$, and the $$pK_a$$ values $$pK_a($$ethanol) = 16.0 and $$pK_a($$water) = 15.7, what is the equilibrium constant $$K_{eq}$$ for this reaction at 25°C?

Accepted Answer

$$K_{eq} = 2.0$$

Question 4

For the acid-base reaction $$\mathrm{HO-H + ^-OCH_2CH_3 \rightarrow HO^- + HOCH_2CH_3}$$, what is the value of $$\Delta S^\circ$$ and why?

Accepted Answer

$$\Delta S^\circ \approx 0$$ because the number of molecules does not change during the reaction.

Question 5

Which equation correctly relates the standard free energy change ($$\Delta G^\circ) to $$the equilibrium constant ($$K_{eq}$$)?

Accepted Answer

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

Question 6

In a reaction coordinate diagram, what does the difference in energy between the reactants and the transition state represent?

Accepted Answer

The activation energy ($$E_a) of $$the reaction.

Question 7

A catalyst lowers the activation energy ($$E_a) of a $$reaction. Which of the following is a direct consequence of this effect?

Accepted Answer

The reaction proceeds faster because more molecules have enough energy to reach the transition state.

Question 8

For the acid-base reaction $$\mathrm{HO-H + ^-OCH_2CH_3 \rightarrow HO^- + HOCH_2CH_3}$$, if $$\Delta S^\circ = 0$$, what is the relationship between $$\Delta G^\circ$$ and $$\Delta H^\circ$$?

Accepted Answer

$$\Delta G^\circ = \Delta H^\circ$$

Question 9

Which of the following best explains why not all acids of the same type (e.g., alcohols) have exactly the same strength?

Accepted Answer

Small differences in bond energies and molecular structure affect acid strength.

Question 10

Which of the following is true about the entropy change ($$\Delta S^\circ) in $$most acid-base reactions?

Accepted Answer

$$\Delta S^\circ is $$often close to zero because the number of molecules does not change.

Question 11

A reaction has $$\Delta G^\circ = -0.407$$ kcal/mol and $$\Delta S^\circ = 0. $$What is $$\Delta H^\circ$$ for this reaction?

Accepted Answer

$$\Delta H^\circ = -0.407$$ kcal/mol

Question 12

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

Accepted Answer

It lowers the height of the activation energy barrier without changing the energies of reactants or products.

Question 13

In the context of acid-base reactions, what does the equation $$pK_{eq} = pK_a($$left-side acid) $$- pK_a($$right-side acid) allow you to determine?

Accepted Answer

The equilibrium constant for the acid-base reaction.

Question 14

Which of the following is a green chemistry benefit of using a catalyst in a chemical process?

Accepted Answer

Catalysts lower the activation energy, reducing the energy required and making the process more sustainable.

Question 15

If a reaction coordinate diagram shows a lower activation energy for the forward reaction than for the reverse, what can you conclude?

Accepted Answer

The forward reaction is faster than the reverse reaction.

Question 16

Which of the following is true about the transition state in an acid-base reaction?

Accepted Answer

It is a high-energy, unstable arrangement where bonds are partially broken and formed.

Question 17

In the Arrhenius equation, what does the frequency factor ($$A) $$represent?

Accepted Answer

The number of collisions with correct orientation per unit time.

Question 18

Which of the following best explains why the enthalpy change ($$\Delta H^\circ) in $$acid-base reactions is related to the relative strengths of the acids and bases involved?

Accepted Answer

Stronger acids and bases have larger differences in bond energies, affecting $$\Delta H^\circ.$$

Question 19

A reaction has $$\Delta G^\circ = \Delta H^\circ - T\Delta S^\circ. If$$ $$\Delta S^\circ = 0$$, what is the effect of temperature on $$\Delta G^\circ$$?

Accepted Answer

$$\Delta G^\circ is $$independent of temperature.

lecture 16

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