Q: A reaction has $$\Delta H = -10$$ kcal/mol and $$\Delta S = -0.02$$ kcal/(mol·K). At $$T = 298 K$$, what is $$\Delta G$$?

$$\Delta G = -10 - (298 \times -0.02) = -10 + 5.96 = -4.04$$ kcal/mol

Question 1

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

Accepted Answer

Homolytic cleavage produces radicals, while heterolytic cleavage produces ions.

Question 2

Given the following reaction: $$\mathrm{CH_3CH_2Br} + \mathrm{Br_2$} \rightarrow \mathrm{CH_3CH_2Br_2}$$, use the bond dissociation energies below to calculate $$\Delta H$$ for the reaction. Assume the following bond energies: $$\mathrm{Br-Br}$$: 46 kcal/mol, $$\mathrm{C-Br}$$: 70 kcal/mol. The reaction breaks one $$\mathrm{Br-Br}$$ bond and forms one $$\mathrm{C-Br}$$ bond.

Accepted Answer

$$\Delta H = 46 - 70 = -24$$ kcal/mol

Question 3

Which of the following changes will increase the entropy ($$S) of a $$system?

Accepted Answer

Allowing a gas to expand into a larger volume.

Question 4

Which equation correctly relates Gibbs Free Energy ($$\Delta G$$), enthalpy ($$\Delta H$$), and entropy ($$\Delta S$$)?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Question 5

A reaction has $$\Delta H = -10$$ kcal/mol and $$\Delta S = -0.02$$ kcal/(mol·K). At $$T = 298 K$$, what is $$\Delta G$$?

Accepted Answer

$$\Delta G = -10 - (298 	imes -0.02) = -10 + 5.96 = -4.04$$ kcal/mol

Question 6

Which of the following best describes the relationship between the equilibrium constant ($$K_{eq}) $$and standard Gibbs Free Energy change ($$\Delta G^\circ$$)?

Accepted Answer

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

Question 7

For the reaction $$A + B ightarrow C + D$$, the rate law is $$	ext{Rate} = k[A]^2[B]. $$What is the overall order of the reaction?

Accepted Answer

Third order

Question 8

Which factor will NOT increase the rate constant ($$k) of a $$chemical reaction?

Accepted Answer

Decreasing the concentration of reactants

Question 9

According to the Hammond Postulate, the structure of the transition state most closely resembles:

Accepted Answer

The species (reactants or products) closest in energy to the transition state

Question 10

Which of the following is a correct statement about nucleophiles and electrophiles?

Accepted Answer

Nucleophiles are electron-rich species that donate electrons to electrophiles.

Question 11

Which arrow-pushing pattern is involved when a lone pair attacks an electron-deficient atom to form a new bond?

Accepted Answer

Nucleophilic attack

Question 12

In a carbocation rearrangement, which shift is most likely to occur to stabilize the carbocation?

Accepted Answer

Beta-hydride shift

Question 13

Which of the following reactions is most likely to be reversible?

Accepted Answer

Nucleophilic attack

Question 14

Which of the following best explains why a catalyst increases the rate of a reaction?

Accepted Answer

It lowers the activation energy ($$E_a) $$required for the reaction.

Question 15

Which of the following is true about the energy diagram of an exothermic reaction?

Accepted Answer

The products are lower in energy than the reactants.

Question 16

A reaction has a large negative $$\Delta G^\circ. $$What can you infer about the equilibrium constant $$K_{eq}$$?

Accepted Answer

$$K_{eq} is $$much greater than 1.

Question 17

Which of the following is NOT a characteristic pattern of arrow pushing in organic reaction mechanisms?

Accepted Answer

Formation of a pi bond

Question 18

Which of the following statements about entropy ($$S) is $$correct?

Accepted Answer

Entropy is a measure of the randomness or disorder of a system.

Question 19

Which of the following best describes the effect of increasing temperature on the rate constant ($$k) $$for a reaction?

Accepted Answer

The rate constant increases.

Organic Chemistry Chapter 6: Chemical Reactivity and Mechanisms

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