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Exam 4: The Study of Chemical Reactions

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Question 1

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The rate of a reaction typically increases as the temperature increases because:

A) the A term in the Arrhenius equation increases.
B) the fraction of molecules with kinetic energy greater than E_a increases.
C) the activation energy decreases.
D) the activation energy increases.
E) the molecules make more collisions with the wall of the reaction vessel.

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Question 2

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What is the hybridization of the positively charged carbon in (CH₃)₃C⁺?

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Question 3

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Which H atom in the molecule shown will be most readily abstracted by a bromine radical?

Consider the following substitution reaction with a ΔG° value of -91.1 kJ/mole. HO- + CH₃Cl ↔ CH₃OH + Cl- Given this information which of the following statements must be true? (R = 8.315 J/mole K)

The relative reactivity of the 1°: 2°: 3° hydrogens of (CH₃)₃CCH₂CH₃ in free radical chlorination is 1: 3.8: 5.0. Provide the structure of each monochlorination product, and estimate the relative amount of each in the mixture of monochlorinated products.

How many secondary hydrogens are present in the hydrocarbon below?

Predict the major monobromination product in the following reaction. (CH₃)₃CCH₂CH₃ + Br₂

Does one expect ΔS° in a propagation step of the free-radical chlorination of methane to be greater than zero, less than zero, or approximately equal to zero? Briefly explain your choice.

Write the structures of all of the monobromination products of 1,1,3,3-tetramethylcyclobutane.

Explain how the termination step in a free-radical chain reaction stops the chain.

Write a detailed, stepwise mechanism for the following reaction.

If a reaction is exothermic, then:

Consider the transformation of A to B (i.e., A → B). If at equilibrium at 25°C the concentration of A is 20% of the initial concentration of A, determine the value of ΔG° (in kcal/mol) for this reaction. R = 1.987 cal/mol∙K.

In the reaction of Cl₂ with ethane and UV light, which of the following reactions would be a propagation event(s) ? I. Cl∙ + CH₃-CH₃ → CH₃-CH₂-Cl + H∙ II. Cl∙ + CH₃-CH₃ → CH₃-H₂C∙ + HCl III. Cl∙ + CH₃-H₂C∙ → CH₃-CH₂-Cl IV. Cl₂ + CH₃-H₂C∙ → CH₃-CH₂-Cl + Cl∙ V. Cl_{2 + UV light} → C l∙ + Cl∙

Consider the three-step mechanism for the reaction of A through intermediates B and C to produce D shown below. A → B E_a = 15 kcal/mol, ΔH° = 13 kcal/mol B → C E_a = 10 kcal/mol, ΔH° = -6 kcal/mol C → D E_a = 2 kcal/mol, ΔH° = -20 kcal/mol What's the enthalpy difference between reactant A and intermediate C?

Given a K of 0.45 at 25°C, calculate the corresponding DG° in kJ/mol. [R = 8.314 J/K∙ mol]

Which of the following correctly expresses the standard Gibbs free energy change of a reaction in terms of the reaction temperature (T) and equilibrium constant (K) ?

When the reaction between methane and chlorine is photochemically initiated, which of the following compounds $\underline{\text{ cannot }}$ be formed through a termination reaction?

If the equilibrium constant (K_eq) of a reaction is 0.5 then which of the following that must be true?

What is the hybridization of the negatively charged carbon in (CH₃)₃C:^-?