$$H^- + H^- \rightarrow H_2$ with $$\Delta H^\circ = -436\ \text{kJ mol}^{-1}$$

Question 1

Which of the following best describes a Lewis acid?

Accepted Answer

A compound that accepts an electron pair from another species.

Question 2

Which of the following reactions is an example of a Brønsted-Lowry acid/base reaction?

Accepted Answer

$$HO^- + HCl \rightarrow H_2O + Cl^-$$

Question 3

Which factor most strongly stabilizes the conjugate base of phenol compared to ethanol?

Accepted Answer

Resonance delocalization of the negative charge.

Question 4

Given the reaction $$HCl + H_2O \rightarrow H_3O^+ + Cl^-$$, which species acts as the Brønsted-Lowry base?

Accepted Answer

$$H_2O$$

Question 5

Which statement about $$pK_a is $$correct?

Accepted Answer

A lower $$pK_a$$ value indicates a stronger acid.

Question 6

Which of the following best explains why $$HF is a $$weaker acid than $$HI$$?

Accepted Answer

The $$F^-$$ ion is smaller and less able to stabilize the negative charge.

Question 7

Which of the following is the correct expression for the $$pK_a of an $$acid $$HA$$?

Accepted Answer

$$pK_a = -\log K_a = -\log \left( \frac{[A^-][H_3O^+]}{[HA]} \right)$$

Question 8

Which of the following structural features would increase the acidity of a molecule?

Accepted Answer

Increasing resonance stabilization of the conjugate base.

Question 9

Which of the following statements about thermodynamics and chemical reactions is correct?

Accepted Answer

A reaction with $$\Delta G^\circ \u003c 0 is $$thermodynamically favored.

Question 10

Which of the following best describes the effect of temperature on the spontaneity of a reaction?

Accepted Answer

Increasing temperature can make a reaction with positive $$\Delta S^\circ$$ more spontaneous.

Question 11

Which of the following is an example of an exothermic reaction?

Accepted Answer

$$H^- + H^- ightarrow H_2$ with $$\Delta H^\circ = -436\ 	ext{kJ mol}^{-1}$$

Question 12

Which of the following factors does NOT contribute to the stabilization of a conjugate base?

Accepted Answer

Increasing electron density on the atom bearing the charge.

Question 13

Which of the following is the correct relationship between Gibbs free energy and equilibrium constant?

Accepted Answer

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

Question 14

Which of the following acids has the lowest $$pK_a$$ value and is therefore the strongest acid?

Accepted Answer

$$H_2SO_4$$

Question 15

Which of the following statements about the effect of atomic size on acidity is correct?

Accepted Answer

A larger atomic size of the anion stabilizes the conjugate base, increasing acidity.

Question 16

Which of the following is a consequence of the Third Law of Thermodynamics?

Accepted Answer

The entropy of a perfect crystal at $$0\ 	ext{K} is $$zero.

Question 17

Which of the following best explains why para-nitrophenol is more acidic than phenol?

Accepted Answer

The nitro group increases resonance stabilization of the conjugate base.

Question 18

Which of the following is true about the relationship between acid strength and conjugate base strength?

Accepted Answer

The stronger the acid, the weaker its conjugate base.

Question 19

Which of the following is an example of an acid/base reaction mechanism involving a Lewis acid?

Accepted Answer

$$NH_3$$ + $$BF_3$$ \rightarrow F^-B-$$NH_3$$

Acids, Bases, and Thermodynamics in Organic Chemistry

Study Guide - Practice Questions