Q: Calculate $$\Delta H^\circ$$ for the following reaction using bond dissociation energies: $$CH_4$$ + $$Cl_2$$ \rightarrow CH_3Cl + HCl$$ Given: D$$($$CH_4) = 439$$\ \text{kJ/mol}$$, D$$($$Cl_2) = 243$$\ \text{kJ/mol}$$, D(CH_3Cl) = 428$$\ \text{kJ/mol}$$, D($$HCl) = 431\ \text{kJ/mol}$$

$$\Delta H^\circ = -23\ \text{kJ/mol}$$

Question 1

Which of the following statements best explains why cyclopropane is less stable than cyclohexane?

Accepted Answer

Cyclopropane has significant angle strain due to its bond angles being much less than $$109.5^{\circ}.$$

Question 2

Given the general formula for alkanes $$C_nH_{2n+2}$$, what is the molecular formula for a linear alkane with 7 carbon atoms?

Accepted Answer

$$C_7H_{16}$$

Question 3

Which of the following is the correct IUPAC name for the compound shown below?

A molecule with a five-carbon chain, a methyl group on carbon 2, and an ethyl group on carbon 3.

Accepted Answer

3-ethyl-2-methylpentane

Question 4

Which of the following alkyl groups is correctly described as a 'sec-butyl' group?

Accepted Answer

A four-carbon group attached at the second carbon: $$CH_3CH_2CH(CH_3$)-$$

Question 5

Which conformation of butane is the most stable according to Newman projections?

Accepted Answer

Anti

Question 6

Which of the following statements about the chair conformation of cyclohexane is TRUE?

Accepted Answer

The chair conformation minimizes both angle strain and torsional strain.

Question 7

Which of the following best describes the difference between homolytic and heterolytic cleavage?

Accepted Answer

Homolytic cleavage produces two radicals, while heterolytic cleavage produces a cation and an anion.

Question 8

Calculate $$\Delta H^\circ$$ for the following reaction using bond dissociation energies:

$$CH_4$$ + $$Cl_2$$ ightarrow CH_3Cl + HCl$$

Given: D$$($$CH_4) = 439$$\ 	ext{kJ/mol}$$, D$$($$Cl_2) = 243$$\ 	ext{kJ/mol}$$, D(CH_3Cl) = 428$$\ 	ext{kJ/mol}$$, D($$HCl) = 431\ 	ext{kJ/mol}$$

Accepted Answer

$$\Delta H^\circ = -23\ 	ext{kJ/mol}$$

Question 9

Which halogen is the most selective in free radical halogenation of alkanes?

Accepted Answer

Bromine ($$Br_2)$$

Question 10

According to the Hammond Postulate, which statement is TRUE about the transition state of an endothermic reaction?

Accepted Answer

The transition state resembles the products more than the reactants.

Question 11

Which of the following is the correct IUPAC name for a bicyclic compound with 7 carbons in the bridge, 2 carbons in the first bridge, and 1 carbon in the second bridge?

Accepted Answer

Bicyclo[2.2.1]heptane

Question 12

Which of the following best describes a nucleophile?

Accepted Answer

A species that donates an electron pair to an electrophile.

Question 13

In the free radical halogenation of propane with $$Cl_2$$, which hydrogen is most likely to be abstracted?

Accepted Answer

The hydrogen on the secondary carbon.

Question 14

Which of the following is NOT a step in the free radical halogenation mechanism?

Accepted Answer

Chain rearrangement

Question 15

Which of the following statements about carbocations is TRUE?

Accepted Answer

Carbocations are stabilized by alkyl groups through hyperconjugation.

Question 16

Which cyclohexane conformer is the least stable?

Accepted Answer

Half-chair

Question 17

Which of the following best describes the relationship between activation energy ($$E_a$$), rate of reaction, and temperature?

Accepted Answer

A lower $$E_a$$ leads to a faster reaction rate, and increasing temperature increases the rate.

Question 18

Given the equilibrium concentrations: $$[A] = 0.2\ 	ext{M}$$, $$[B] = 0.8\ 	ext{M}$$, calculate $$\Delta G^\circ at$$ $$298\ 	ext{K}$$ for the reaction $$A ightleftharpoons B.

$$Use $$\Delta G^\circ = -RT \ln K_{eq}$$, $$R = 8.314\ 	ext{J/mol K}.$$

Accepted Answer

$$\Delta G^\circ = -3.43\ 	ext{kJ/mol}$$

Question 19

Which of the following is a correct statement about inhibitors in free radical reactions?

Accepted Answer

Inhibitors slow down or stop the chain reaction by reacting with free radicals.

Alkanes, Cycloalkanes, and Free Radical Reactions: Structure, Nomenclature, and Mechanisms

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