SB 14.7-14.8

Correctly order the steps required to derive the overall rate law for a multistep reaction that has one or more fast initial steps, based on a proposed mechanism. a) Use the rate law is derived for the fast steps to express the concentrations of any intermediates in terms of reactant concentrations b) Write the rate laws for the forward and reverse processes for each fast step that precedes the rate-determining step c) Express the equation of each fast step preceding the rate-determining step as an equilibrium process d) Derive an overall rate law by substituting expressions for intermediate concentrations into the rate law for the rate-determining step

c; b; a; d

A _____ is a substance that increases the rate of a reaction without being consumed. This type of substance is often used up and regenerated during the reaction.

catalyst

The individual steps that make up a reaction mechanism are called _____ reactions or steps.

elementary

A(n) _____ is a protein that acts as a biological catalyst.

enzyme

Which of the following are described by a reaction mechanism? Select all that apply.

-An explanation of the way in which the individual reactants are transformed to products -The sequence of individual steps that make up the reaction -The identities of any reaction intermediates

Which of the following statements correctly describe catalysts?

-Catalysts lower the activation energy of the rate-determining step in the reaction. -Catalysts provide a different mechanism for the reaction.

Which of the following attributes are characteristic of enzymes? Select all that apply.

-High specificity -High rates of activity

Which of the following can provide experimental data that supports a proposed reaction mechanism?

-Isotope labeling experiments -Detection or characterization of a reaction intermediate

Which of the following are examples of heterogeneous catalysis?

-Liquid petroleum products react with hydrogen gas on the surface of platinum metal. -Oxides of nitrogen are converted to O2 and N2 in a catalytic converter.

Which of the following elementary reactions are unimolecular

-PCl5 (g) → PCl3 (g) + Cl2 (g) -N2O4 (g) → 2NO2 (g)

Which of the following options correctly describe the different models of enzyme action? Select all that apply.

-The enzyme forms an enzyme-substrate complex, which is then converted to product. -The enzyme active site can modify its shape to a certain extent to accommodate different substrates. -The lock-and-key model proposed that the active site of an enzyme provides a precise fit for its substrate.

Select all the options that correctly describe a reaction intermediate.

-The formation of a reaction intermediate is described in the reaction mechanism. -A reaction intermediate is formed in one step of a reaction and used up in a later step.

Which options correctly describe how to assess the validity of a mechanism proposed for a multistep reaction with one or more fast initial steps, given the experimentally determined rate law? Select all that apply.

-The overall rate law will reflect the concentrations of any reactants involved in all steps up to and including the rate-determining step. -Intermediate concentrations are expressed in terms of reactant concentrations using rate laws for the fast steps.

Select the statements that correctly describe the kinetics of an elementary reaction.

-The rate law for an elementary step can be deduced from its balanced chemical equation. -For an elementary reaction, reaction order equals molecularity. -The elementary reaction 2HI (g) → H2 (g) + I2 (g) follows second-order kinetics.

Which of the following criteria must be met for a reaction mechanism to be considered valid? Select all that apply.

-The rate law for the rate-determining step must correlate with the experimentally determined rate law. -The elementary steps must add up to the overall balanced reaction.

Select all the statements that correctly describe the rate-determining step in any reaction.

-The rate-determining step is always the slowest step in the reaction. -The rate law for the rate-determining step is determined using experimental data obtained for the overall reaction. -The rate-determining step is an elementary step.

A chemical reaction occurs in three elementary steps and is exothermic overall. The first step is the slowest step. Select all the statements that correctly describe the potential energy profile for this reaction.

-There will be three peaks in the energy profile. -The energy of the products will be lower than the energy of the reactants.

The use of finely powdered palladium metal to catalyze the reaction shown below is an example of ______ catalysis. C6H12 (l) + H2 (g) → C6H14 (l)

heterogeneous Reason: Solid palladium metal in a liquid reaction medium is an example of heterogeneous catalysis.

A ______ catalyst is in a difference phase from the reactants, whereas a ______ catalyst is dispersed in the same phase as the reactants.

heterogeneous, homogeneous

The addition of aqueous H2SO4 to catalyze the hydrolysis shown below would be an example of ______ catalysis. C4H8O2 (aq) + H2O (l) → C2H4O2 (aq) + C2H6O (aq)

homogeneous Reason: Since sulfuric acid is soluble in the aqueous reaction medium, it is an example of homogeneous catalysis.

A species that is formed during one step of a reaction and used up in a subsequent step is called a reaction _____

intermediate

The fact that a proposed reaction mechanism is consistent with the observed rate law is not sufficient to prove that the mechanism is correct. Additional experiments are typically necessary to validate a proposed mechanism. These may include attempts to detect a(n) ______; additionally, the paths of specific atoms through a reaction mechanism can be traced through the use of ______. Multiple choice question.

intermediate; isotopes

The reaction _____ provides information about the individual steps of a reaction, and identifies any reaction _____ , which are formed during one step and consumed in a subsequent step.

mechanism; intermediates

An elementary step is characterized by its _____, which is equal to the number of reactant particles in the step. Multiple choice question.

molecularity

homogeneous catalyst

reactants and catalyst are dispersed in a single phase

heterogeneous catalyst

reactants and catalyst are in different phases

For a proposed reaction mechanism to be valid, the rate law determined from experimental data must match the rate law for the ______.

slowest reaction step Reason: The slowest step is the rate-determining step. The rate law for this step must match the experimentally determined rate law.

The _____ step in any reaction sequence determines the rate law for the overall reaction. This step is called the rate-_____ step.

slowest; determining

An enzyme binds to a reactant, which is called the _____, at the _____ site of the enzyme.

substrate; active

What is the molecularity of the elementary step A (g) + B (g) + C (g) → D (g)?

termolecular

In an example of homogeneous catalysis, the reactant(s) and the catalyst are in ______ phase(s).

the same

What is an elementary reaction?

Each step that makes up a reaction mechanism

Lock-and-Key Model

Only a substrate whose shape exactly fits the active site can bind.

Which of the following species will be included in the overall rate law for a multistep reaction involving 2 or more initial fast steps?

Reactants involved in all steps up to and including the rate-determining step

Which statement correctly describes the active site of an enzyme?

The active site is where the enzyme-catalyzed reaction occurs.

True or false: The rate law for an elementary step can be deduced from its reaction stoichiometry (i.e., from the balanced equation for the step).

True Reason: Since an elementary reaction occurs in ONE step, its rate law can be deduced from the reaction stoichiometry.

a homogeneous catalyst is

aqueous

The rate law for the reaction 2NO2 (g) + F2 (g) → 2NO2F (g) is found to be rate = k[NO2][F2]. Which of the following proposed mechanisms is consistent with this rate law?

1: NO2 + F2 → NO2F + F (slow) 2: NO2 + F → NO2F (fast) Reason: The rate law for the rate-determining step is the same as the experimentally determined rate law.

What is molecularity?

The number of reactant particles that react in an elementary step

Flexible Enzyme Activity

The shape of the active site can be modified to fit a substrate.

What is the reaction intermediate in this two-step mechanism? (1) X + O3 → XO + O2 (2) XO + O → X + O2

XO

enzyme

a biological catalyst

a heterogenous catalyst is

a solid