Question 1

Which statement best explains why long bonds are generally weaker than short bonds?

Accepted Answer

Long bonds are formed between larger atoms, which have less effective orbital overlap, resulting in weaker bonds.

Question 2

In the gas phase, which type of bond cleavage produces free radicals?

Accepted Answer

Homolytic cleavage

Question 3

Which of the following best describes the effect of entropy ($$\Delta S) in a $$gas-phase reaction with no solvent?

Accepted Answer

Entropy can be ignored, so $$\Delta G \approx \Delta H.$$

Question 4

Given the reaction $$\mathrm{CH_4$ + Cl_2$ \xrightarrow{hv} CH_3Cl + HCl}$$, which bonds are broken and which are formed?

Accepted Answer

Broken: C-H and Cl-Cl; Formed: C-Cl and H-Cl

Question 5

Which of the following best describes the role of $$\Delta H$$ and $$\Delta S in $$determining the spontaneity of a reaction?

Accepted Answer

A reaction is spontaneous if $$\Delta G = \Delta H - T\Delta S is $$negative.

Question 6

What is the bond dissociation energy (BDE) for the H-H bond, given that $$\Delta H$$ for $$\mathrm{H_2$ \rightarrow 2H} is$$ $$+104$$ kcal/mol?

Accepted Answer

$$104$$ kcal/mol

Question 7

Which factor increases the rate of a chemical reaction according to collision theory?

Accepted Answer

Increasing the concentration of reactants

Question 8

For the reaction $$\mathrm{A + B \rightarrow C + D}$$, if two molecules become one, what is the sign of $$\Delta S$$?

Accepted Answer

$$\Delta S is $$negative

Question 9

Which of the following is true about the stability of alkyl radicals?

Accepted Answer

Tertiary radicals are more stable than primary radicals due to hyperconjugation.

Question 10

In a free radical halogenation of methane, why is it difficult to obtain only monosubstituted products?

Accepted Answer

All hydrogens are equally reactive, so multiple substitutions occur sequentially.

Question 11

Which of the following best describes the transition state (TS) in an endothermic reaction?

Accepted Answer

The TS resembles the products more than the reactants.

Question 12

What is the effect of increasing temperature on the rate of a reaction?

Accepted Answer

The rate increases because more molecules have enough energy to overcome the activation barrier.

Question 13

Which of the following is the correct expression for the equilibrium constant $$K_{eq}$$ for the reaction $$\mathrm{A \rightleftharpoons B}$$?

Accepted Answer

$$K_{eq} = \dfrac{[B]}{[A]}$$

Question 14

If the bond dissociation energy (BDE) for $$\mathrm{CH_3$-H} is$$ $$104$$ kcal/mol and for $$\mathrm{CH_2CH_2-H} is$$ $$98$$ kcal/mol, which radical is more stable?

Accepted Answer

Ethyl radical

Question 15

Which of the following is a correct statement about the use of electron-flow arrows in reaction mechanisms?

Accepted Answer

The arrow's tail shows where electrons start in the reactant, and the head shows where they go in the product.

Question 16

Which of the following best explains why $$\mathrm{F_2$}$$ has a higher bond dissociation energy than $$\mathrm{I_2$}$$?

Accepted Answer

Fluorine atoms are smaller, leading to stronger orbital overlap and a stronger bond.

Question 17

In the reaction $$\mathrm{CH_4$ + Cl_2$ \xrightarrow{hv} CH_3Cl + HCl}$$, what is the overall $$\Delta H^\circ if $$the bonds broken are $$104$$ kcal/mol (C-H) and $$58$$ kcal/mol (Cl-Cl), and the bonds formed are $$85$$ kcal/mol (C-Cl) and $$103$$ kcal/mol (H-Cl)?

Accepted Answer

$$\Delta H^\circ = (104 + 58) - (85 + 103) = -26$$ kcal/mol

Question 18

Which of the following is a correct statement about the effect of a large positive $$\Delta S on $$reaction spontaneity?

Accepted Answer

A large positive $$\Delta S$$ can overcome a small positive $$\Delta H$$, making $$\Delta G$$ negative.

Bond Strengths, Thermodynamics, and Free Radical Reactions in General Chemistry

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