6. Thermodynamics and Kinetics

Showing 5 of 5 videos

Practice this topic

If the transition state has a high energy relative to the energies of the reactants and products, what does this say about the reaction?

266

Which equation would you use to calculate the rate of a reaction?

223

Complete the following sentence: Breaking bonds ____________.

244

Which reaction coordinate diagram matches the following acid/base reaction?

251

In an enantioselective reaction, what best accounts for the formation of one enantiomer preferentially over the other enantiomer?

192

The bond angles in a regular polygon with n sides are equal to 180° - 360°/n a. What are the bond angles in a regular octagon? b. What are the bond angles in a regular nonagon?

278

The bromination of methane proceeds through the following steps: 1. Br2 + 2 Br• ΔH° (per mole)/+190 kJ (45 kcal) Ea (per mole)/ 190 kJ (45 kcal) 2. CH4 + Br• —> CH3+ HBr +73 kJ (17 kcal) 79 kJ (19 kcal) 3. • CH3 + Br2 —> CH3Br + Br -112 kJ (-27 kcal) 4 kJ (1 kcal) a. Draw a complete reaction-energy diagram for this reaction. b. Label the rate-limiting step.

1929

Draw a reaction-energy diagram for a one-step exothermic reaction. Label the parts that represent the reactants, products, transition state, activation energy, and heat of reaction.

a. Draw the reaction-energy diagram for the following reverse reaction: •CH3 + HCl —> CH4 + Cl•

585

a. Draw a reaction-energy diagram for the following reaction: •CH3 + CL2 —> CH3Cl + Cl•

190

•CH3 + CL2 —> CH3Cl + Cl• The activation energy is 4 kJ/mol (1 kcal/mol), and the overall ΔH° for the reaction is -110 kJ/mol (-27 kcal/mol). b. Give the equation for the reverse reaction. c. What is the activation energy for the reverse reaction?

402

Draw a reaction-energy diagram for a two-step endothermic reaction with a rate-limiting second step.

443

a. Draw an approximate reaction-energy diagram for the acid–base reaction of phenol (see below) with 1-molar aqueous sodium hydroxide solution.

b. On the same diagram, draw an approximate reaction-energy diagram for the acid–base reaction of tert-butyl alcohol (see below) with 1-molar aqueous sodium hydroxide solution.

Phenol, <IMAGE> pKa= 10.0

Tert-butyl alcohol <IMAGE> pKa=18.0

rank

Given the reaction coordinate diagram for the reaction of A to form G, answer the following questions:

a. How many intermediates are formed in the reaction? b. Which letters represent transition states? c. What is the fastest step in the reaction? d. Which is more stable: A or G? e. Does A or E form faster from C? f. Which is the more stable intermediate?

335

Draw a reaction coordinate diagram for the following reaction in which C is the most stable and B the least stable of the three species and the transition state going from A to B is more stable than the transition state going from B to C:

a. How many intermediates are there? b. How many transition states are there? c. Which step has the greater rate constant in the forward direction? d. Which step has the greater rate constant in the reverse direction?

1220

a. Which step in the reaction coordinate diagram shown here has the greatest free energy of activation in the forward direction? b. Is the first-formed intermediate more apt to revert to reactants or go on to form products? c. Which step is the rate-determining step of the reaction?

Draw a reaction coordinate diagram for a one step reaction that has the following values of Eₐ and ∆H. (a) Eₐ = 9 kcal/mol ; ∆H° = + 4kcal/mol

252

Draw a reaction coordinate diagram for a one step reaction that has the following values of Eₐ and ∆H. (b) Eₐ = 2 kcal/mol ; ∆H° = -17kcal/mol

227

Draw a reaction coordinate diagram for a one step reaction that has the following values of Eₐ and ∆H. (c) Eₐ = 5 kcal/mol ; ∆H° = 0kcal/mol

274

For the reaction coordinate diagram shown, is the forward or reverse reaction faster?

349

(••) Draw a reaction coordinate diagram, making sure to label reactants (R), products (P), intermediates (I), transition states (‡), activation energies ( Eₐ) , and , ∆G° for each of the following. (a) an exothermic, one-step reaction

265

b. Draw a reaction coordinate diagram for the reaction. (Hint: An alkyl halide is more stable than an alkene.)

318

Draw an approximate reaction-energy diagram showing the curves for the two possible pathways for ionic addition of HBr to 1-methylcyclohexene. (a) Formation of the major product, 1-bromo-1-methylcyclohexane, and ( b) formation of the minor product, 1-bromo-2-methylcyclohexane. Point out how these curves show that 1-bromo-1-methylcyclohexane should be formed faster.

786

On a single graph, draw the reaction coordinate diagram for the addition of one equivalent of HBr to 2-methyl-1,3-pentadiene and for the addition of one equivalent of HBr to 2-methyl-1,4-pentadiene. Which reaction is faster?

462

Given that A is more stable than B, draw a reaction coordinate diagram that rationalizes the fact that A forms more quickly than B in the following reaction.

257

(•••) Draw a reaction coordinate diagram for the following transformation. Label all product, intermediates, and substrates.

216

(••) For each of the reaction coordinate diagrams shown,

(i) indicate the number of steps in the reaction,

(ii) label the intermediates,

(iii) identify the rate-determining step, and

(iv) tell whether K_eq is greater than, less than, or equal to zero.

(a) <IMAGE>

210

(d) a slightly exothermic, three-step reaction where the third step is rate-determining.

231

The alkyl carbocation is estimated to be 15 kcal/mol more stable than the alkenyl carbocation. If this is also the difference in the energies of the transition state leading to each, what is the expected rate difference?

<IMAGE>

214

Show a reaction coordinate diagram for the two processes in Figure 13.41 that rationalizes pathway B as the one that gives the major product.

<IMAGE>

234

Using Equation 5.8, calculate the difference in transition state energies that lead to the rate differences shown in Figure 24.35.

<IMAGE>

182

(b) an exothermic, two-step reaction where the second step is rate-determining

Draw a reaction-energy diagram for the propagation steps of the free-radical addition of HBr to isobutylene. Draw curves representing the reactions leading to both the Markovnikov and the anti-Markovnikov products. Compare the values of ∆Gº and Ea and for the rate-limiting steps, and explain why only one of these products is observed.

Draw a reaction coordinate diagram for a reaction in which

a. the product is thermodynamically unstable and kinetically unstable.

b. the product is thermodynamically unstable and kinetically stable.

219

Draw a reaction coordinate diagram for a two-step reaction in which the first step is endergonic, the second

step is exergonic, and the overall reaction is endergonic. Label the reactants, products, intermediates, and

transition states.

151

The acid dissociation constant (Ka) for loss of a proton from cyclohexanol is 1*10-16.

a. Draw a reaction coordinate diagram for loss of a proton from cyclohexanol.

<IMAGE>

156

The reaction of tert-butyl chloride with methanol

(CH3)3C—Cl Tert-butylchloride + CH3—OH methanol —> (CH3)C—OCH3 methyltert-butylether + HCl

is found to follow the rate equation

rate= Kt[(CH3)3C—Cl]

b. What is the kinetic order with respect to methanol?

143

Under certain conditions, the bromination of cyclohexene follows an unusual rate law:

rate= Kr[cyclohexene][Br2]^2

c. What is the overall kinetic order?

139

The following reaction is a common synthesis used in the organic chemistry laboratory course.

CH3CH2CH2CH2Br 1-bromobutane + CH3O- methoxide ion —> CH3OH(methanol solvent—> CH3CH2Ch2Ch2OCH3 methoxybutane + Br- bromide ion

When we double the concentration of methoxide ion (CH3O–), we find that the reaction rate doubles. When we triple the concentration of 1-bromobutane, we find that the reaction rate triples.

a. What is the order of this reaction with respect to 1-bromobutane? What is the order with respect to methoxide ion?

Write the rate equation for this reaction.

What is the overall order?

122

Treatment of tert-butyl alcohol with concentrated HCl gives tert-butyl chloride.

Tert-butyl alcohol <IMAGE> + H⁺ + Cl^- → tert-butyl chloride <IMAGE> + H₂O

When the concentration of H⁺ is doubled, the reaction rate doubles.

When the concentration of tert-butyl alcohol is tripled, the reaction rate triples.

When the chloride ion concentration is quadrupled, however, the reaction rate is unchanged.

Write the rate equation for this reaction.

123

When a small piece of platinum is added to a mixture of ethene and hydrogen, the following reaction occurs:

Ethene <IMAGE> + H2 hydrogen Pt catalyst —> ethane <IMAGE>

Doubling the concentration of hydrogen has no effect on the reaction rate. Doubling the concentration of ethene also has no effect.

b. Write the unusual rate equation for this reaction.

c. Explain this strange rate equation, and suggest what one might do to accelerate the reaction.

104

How will the rate of the reaction between bromomethane and hydroxide ion be affected if the following changes in concentration are made?

c. The concentration of the alkyl halide is cut in half and the concentration of the nucleophile is doubled.

(••) For the following acid–base pairs, (v) show a mechanism for the reaction; and (vi) draw a reaction coordinate diagram. (f)

238

(••) For the following acid–base pairs, (iii) predict the favored side of equilibrium; (iv) calculate ; (h)

279

Identify the nucleophile and the electrophile in the following acid–base reactions: a.

1173

Within the following pairs, pick which reaction you would expect to be faster based on having a higher value of the frequency factor (A).

(b) <IMAGE>

175

(••) For the following acid–base pairs,

(vi) draw a reaction coordinate diagram.

(e) <IMAGE>

152

(•••) Parts (a)–(f) of this assessment refer to the rotation around the single bond of ethane. (c) Write the rate law for this reaction.

205

All things being equal, would you expect a first-order reaction to be faster or slower than a second-order reaction?

186

(•••) Parts (a)–(f) of this assessment refer to the rotation around the single bond of ethane. (b) What is the order of the reaction with regard to ethane?

205

When a small piece of platinum is added to a mixture of ethene and hydrogen, the following reaction occurs: Ethene

+ H2 hydrogen Pt catalyst —> ethane

Doubling the concentration of hydrogen has no effect on the reaction rate. Doubling the concentration of ethene also has no effect. a. What is the kinetic order of this reaction with respect to ethene? With respect to hydrogen? What is the overall order?

523

The reaction of tert-butyl chloride with methanol (CH3)3C—Cl Tert-butylchloride + CH3—OH methanol —> (CH3)C—OCH3 methyltert-butylether + HCl is found to follow the rate equation rate= Kt[(CH3)3C—Cl] a. What is the kinetic order with respect to tert-butyl chloride?

Chapter 5 taught us that chemical reactions are random collisions. Experimentally, how can we make molecules collide more often?

179

The reaction of tert-butyl chloride with methanol (CH3)3C—Cl Tert-butylchloride + CH3—OH methanol —> (CH3)C—OCH3 methyltert-butylether + HCl is found to follow the rate equation rate= Kr[(CH3)3C—Cl] c. What is the kinetic order overall?

344

The reaction of tert-butyl chloride with methanol (CH3)3C—Cl Tert-butylchloride + CH3—OH methanol —> (CH3)C—OCH3 methyltert-butylether + HCl is found to follow the rate equation rate= Kr[(CH3)3C—Cl] c. What is the kinetic order overall?

Under certain conditions, the bromination of cyclohexene follows an unusual rate law:

+ Br2 —>

rate= Kr[cyclohexene][Br2]^2 a. What is the kinetic order with respect to cyclohexene?

521

The molecule A undergoes a three-step reaction to make B, where the first step is rate determining. Conversely, C can be produced by A in a two-step reaction where the second step is rate determining. Show a reaction coordinate diagram for each reaction, making it clear that the reaction to make C is faster than the reaction to make B.

219

Under certain conditions, the bromination of cyclohexene follows an unusual rate law:

+ Br2 —>

rate= Kr[cyclohexene][Br2]^2 b. What is the kinetic order with respect to bromine?

784

How will the rate of the reaction between bromomethane and hydroxide ion be affected if the following changes in concentration are made? b. The concentration of the alkyl halide is cut in half and the concentration of the nucleophile is not changed.

281

Given the following rate data, how many molecules are in the rate-determining step of this reaction? [Does this fit with the mechanism we learned in Chapter 8?]

200

Given that step 1 of the following reaction is rate determining, write the rate law for the overall reaction.

240

Within the following pairs, pick which reaction you would expect to be faster based on having a higher value of the frequency factor (A). (a)

235

(•••) Parts (a)–(f) of this assessment refer to the rotation around the single bond of ethane. (a) Given that the rate of the reaction is independent of concentration, fill in the missing rates in the following table.

207

How will the rate of the reaction between bromomethane and hydroxide ion be affected if the following changes in concentration are made? a. The concentration of the alkyl halide is not changed and the concentration of the nucleophile is tripled.

316

(•••) For rotation around a bond, the rate constant is equal to the reaction rate. Why?

185

The rate constant for the uncatalyzed reaction of two molecules of glycine ethyl ester to form glycylglycine ethyl ester is 0.6 M - 1s - 1. In the presence of Co2+, the rate constant is 1.5 * 106 M - 1s - 1. What rate enhancement does the catalyst provide?

141

The rate constant for a reaction can be increased by ______ the stability of the reactant or by ______ the stability of the transition state.

142

From the Arrhenius equation, predict how

a. increasing the experimental activation energy affects the rate constant for a reaction.

144