Chem Ch. 15

calculate the average rate of reaction between t = 50.0 s and t = 100.0 s for the reaction between Br2 and HCOOH, given the data provided.

+3.28 × 10-5 M/s

Which of the following options correctly express rate for the reaction H2 (g) + O2 (g) → H2O2 (l)? Select all that apply.

- Δ[H2]ΔtΔ[H2]Δt Δ[H2O2]Δt

Every chemical reaction proceeds through a high-energy unstable species as reactants are converted to products and bonds are in the process of being formed and/or broken. This unstable species is called a(n)

activated complex and or transition state

The _____ energy of a reaction is the energy threshold that colliding molecules must exceed in order to react.

activation

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

Collision theory states that particles will react when they ____ with each other. For a reaction to be successful, the particles must have enough ______ energy

collide, kinetic

Reaction rate is expressed as a change in the _____ of reactants or products as a function of .____________

concentration, time

Reaction rates are expressed as the change in _____ over a period of ____

concentration, time

As a chemical reaction proceeds, the concentrations of the reactants will _____ . This results in a _____ in the rate of the reaction with time.

decrease, decrease

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

elementary

For a collision to be effective, the colliding particles must have enough _______________ and the appropriate molecular

energy/ KE , positioning

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

heterogeneous

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

select all the statements that correctly describe the instantaneous reaction rate

instantaneous rate is calculated by finding the slope of a tangent to the curve of concentration versus time at any point on the curve. The instantaneous reaction rate is proportional to reactant concentration.

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 ______.

intermediate; isotopes

For the reaction aA + bB → cC + dD, the rate law is Rate = k[A]x[B]y. Match the appropriate definition with each term of the rate law.

k = rate constant x,y - reactant order [A][B] = reactant conentrations

An increase in temperature causes the reaction rate to increase. At a higher temperature the average _____ energy of the particles is greater, and the fraction of particles with enough energy to exceed the

kinetic, activation

When two molecules in motion collide, ______ energy is partially converted to ______ energy; this may result in the breaking of bonds.

kinetic, vibrational

The units for reaction rate are given by _____.

mol/L⋅s

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

molecularity

The rate of a reaction is expressed as Δ[A]ΔtΔ[A]Δt. If A is a reactant a _____ sign must be added in front of this expression in order for the rate to have a _____ value. This is not necessary if A is a product.

negative; positive

In the rate law rate = k[A]x[B]y, the exponents x and y are called the reaction ____ If x = 1, the reaction is said to be _____ with respect to reactant A.

orders, first order

An energy profile for a reaction plots ______ energy versus reaction ______.

potential, progress

Enzyme

protein that acts as a biological catalyst

Which equation properly expresses the rate of a reaction in which a gas is produced, based on the partial pressure of the gas?

rate = ΔPgasRTΔt

select all the options that correctly express the rate of the given reaction in terms of reactant and product concentrations. 2ClO (g) → Cl2 (g) + O2 (g)

rate = Δ[Cl2]ΔtΔ[Cl2]Δt rate = - 1212Δ[ClO]Δt

the ____ constant, given the symbol k, expresses the proportionality between reactant concentration and reaction rate for a given reaction. The value of k is constant at constant _______

rate, temperature

homogeneous catalyst

reactants and catalyst are dispersed in a single phase

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

same

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

the ___ tep 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.

substrates, active

If a lump of solid reactant is ground finely it will have a greater ____ area for reaction, leading to a larger number of ____ between particles and therefore an increase in reaction rate.

surface, collisions

Using a plot of [reactant] versus time, the instantaneous reaction rate is calculated by finding the slope of a(n) _______ to the curve at any particular time. Instantaneous rate _____ as [reactant] decreases. (Note: this question contains no graph.) Listen to the complete question

tangent, decreases

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.

Which of the following statements correctly describe how a rate law is determined? Select all that apply.

the rate law is determined by measuring the initial reaction rate for different reactant concentrations. The value of k can be calculated from a single experiment once the reaction orders are known. If there is more than one reactant present the reaction orders will usually be determined individually.

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

for the general rate law rate = k[A]x[B]y, the overall reaction order is given by _____.

x + y

Select the option that correctly expresses the rate of the following general reaction in terms of the change in concentration of each of the reactants and products: A (g) + 2B (g) → C (g)

Δ[A]ΔtΔ[A]Δt = - 1212 Δ[B]ΔtΔ[B]Δt = Δ[C]Δt

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)

Write a balanced chemical equation for the reaction that has the following rate equation: Rate = - 1212Δ[N2O5]ΔtΔ[N2O5]Δt = 1414Δ[NO2]ΔtΔ[NO2]Δt = Δ[O2]Δt

2N2O5 (g) → 4NO2 (g) + O2 (g)

The table shown gives concentration vs. time data for the decomposition of nitrogen dioxide, shown below. What is the average rate of the reaction over the time interval from 20.0 s to 30.0 s? NO2 (g) → NO (g) + 1/2 O2 (g)

5.0 × 10-4 M/s

heterogeneous catalyst

A catalyst that is in a different phase from that of the reactant substances.

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 conditions must be satisfied for a collision between reactants to be effective? Select all that apply.

Appropriate molecular orientation Enough energy to overcome Ea

Which of the following statements best describes the effect of reactant concentration on reaction rate?

As reactant concentration increases, the number of reactant collisions increases, which in turn increases the reaction rate.

Why does average reaction rate change over time? (Assume the reaction is not reversible to any appreciable extent.)

As the reaction proceeds, reactant concentrations decrease; hence rate decreases over time.

which of the following species will appear in the overall rate law for the overall reaction 2NO (g) + Br2 (g) → 2NOBr (g), given the mechanism shown?

Br2 NO

Which of the following statements correctly describe catalysts? Select all that apply.

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

What is an elementary reaction?

Each step that makes up a reaction mechanism

Consider the reaction 2H2 (g) + O2 (g) → 2H2O (g). At a particular moment in the reaction, H2 (g) is disappearing at a rate of 0.024 M/s. Select all the statements that correctly describe this reaction.

H2O (g) is being formed at a rate of 0.024 M/s. O2 (g) is being used up at a rate of 0.012 M/s.

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

High specificity High rates of activity

Which of the following changes will cause an increase in the rate of a chemical reaction? Select all that apply. (Assume the reaction is not reversible to any appreciable extent.)

Increasing the concentration of a reactant Grinding a large piece of solid reactant into a fine powder

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? Select all that apply.

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? Select all that apply.

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

A plot of concentration versus time for a particular reaction is shown in the accompanying graphic. What can be deduced about the rate of reaction from this plot?

Rate is decreasing over the course of the reaction.

Which of the following factors will influence the rate of a chemical reaction? Select all that apply.

Reactant concentration Surface area of a solid reactant Reaction temperature

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 of the following options correctly describe the principles of collision theory? Select all that apply.

Reaction rate is directly proportional to the number of collisions per second. Collision theory states that in general particles must collide in order to react. When particles collide, some of their kinetic energy is converted to vibrational energy.

which statement correctly describes the active site of an enzyme?

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

Which of the following statements correctly describe the average rate of a reaction? Select all that apply.

The average reaction rate generally decreases with time. Average reaction rate expresses the decrease in reactant particles with time. For the reaction C → D, the average reaction rate is expressed as [D]final−[D]initialtfinal−tinitial[D]final-[D]initialtfinal-tinitial.

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.

Select all the statements that correctly describe the rate-determining step in any 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. The rate-determining step is always the slowest step in the reaction.

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.

Multiple Select Question Select all that apply The reaction of HBr with oxygen gas is represented by the following balanced equation: 4HBr (g) + O2 (g) → 2H2O (g) + 2Br2 (g) A proposed mechanism for this reaction is shown. The rate law is found to be rate = k[HBr]{O2]. Select all the options that correctly describe how this mechanism meets, or does not meet, the criteria for validity.

The rate law is consistent with the proposed mechanism. The elementary steps are logical and physically reasonable.

Why does a hot steel nail placed in oxygen burn slowly, while the same mass of a piece of steel wool burns much more quickly?

The steel wool has a greater surface area for reaction.

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.

1. express 2. write 3. use 4. Derivie

Select all the statements that correctly describe how a chemical reaction is affected by an increase in temperature.

Collisions between reacting particles are more frequent. The average collision energy increases. The reaction rate increases.

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

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. The enzyme forms an enzyme-substrate complex, which is then converted to product.

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 of the following factors are affected by an increase in reactant concentration? Select all that apply.

The number of reactant particles in a given volume The number of reactant collisions The rate of reaction

What is molecularity?

The number of reactant particles that react in an elementary step

Which of the following statements correctly describe the rate constant k for a reaction? Select all that apply.

The rate constant has a constant value for a given reaction at a constant temperature. The rate constant relates reaction rate to reactant concentration.

Which of the following statements correctly describe a rate law for a reaction? Select all that apply. (Assume that the reaction is not reversible to any appreciable extent.)

The rate law relates the rate of reaction to the concentrations of the reactants. The rate law includes the rate constant for the reaction.

The concentration of a reactant in a hypothetical reaction is plotted vs. time in the image shown. Which of the following statements correctly interpret the information shown? Select all that apply.

The rate of the reaction is changing with time. The rate decreases as the reaction proceeds.

Which of the following options correctly interpret the rate law rate = k[H2][NO]2? Select all that apply.

The reaction is second order with respect to NO. If [NO] is doubled while [H2] remains the same, the reaction will occur 4 times faster.

Which of the following conditions must be fulfilled in order to calculate reaction rate using change in pressure over time rather than change in concentration? Select all that apply.

The temperature at which the reaction is carried out must be known. One reactant or product must be a gas.

Which of the following statements correctly describe the transition state of a reaction? Select all that apply.

The transition state only exists at the instant of highest potential energy in the reaction. The transition state species is highly unstable.

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.