CHEM 211 Ch.14
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 Reason: average rate = - 0.00846−0.0101/ (100−50)
Which of the following can be calculated using the two-point form of the Arrhenius equation (given)?
the rate constant at different temperatures the activation energy of the reaction
In an example of homogeneous catalysis, the reactant(s) and the catalyst are in ______ phase(s).
the same
When two reacting particles collide, some of their kinetic energy is converted to _____ energy. If their kinetic energy is large enough, the particles will vibrate strongly, causing chemical ____ to break
vibrational, bonds
The activation energy of a reaction can be determined graphically using the straight-line form of the Arrhenius equation. Identify the components of the straight-line plot used in this determination.
x axis values : 1/T y axis values : ln K slope: -Ea/R intercept: ln A
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]Δt = - 1/2 Δ[B]Δt = Δ[C]Δt
Which of the following options correctly express rate for the reaction H2 (g) + O2 (g) → H2O2 (l)?
- Δ[H2]ΔtΔ[H2]/Δt Δ[H2O2]/Δt
Which of the following conditions must be satisfied for a collision between reactants to be effective?
-Appropriate molecular orientation -Enough energy to overcome Ea
Which of the following statements correctly describe catalysts?
-Catalysts provide a different mechanism for the reaction. -Catalysts lower the activation energy of the rate-determining step in the reaction.
Which of the following statements correctly describe chemical kinetics?
-Chemical kinetics is the study of reaction rates. -Chemical kinetics describes chemical reactions using collision theory. -Chemical kinetics measures how fast reactants are converted into products.
Which of the following options correctly describe the principles of collision theory?
-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. -Reaction rate is directly proportional to the number of collisions per second.
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 reaction rate increases. -The average collision energy increases.
Which of the following can provide experimental data that supports a proposed reaction mechanism?
-Detection or characterization of a reaction intermediate -Isotope labeling experiments
Match the order of the reaction with the information provided about the effect of changing [A] for the reaction A → products.
-If the rate doubles when [A] doubles =first order with respect to A. -If the rate quadruples when [A] doubles =second order with respect to A. -If the rate does not change when [A] doubles= zero order with respect to A.
Which of the following changes will cause an increase in the rate of a chemical reaction?
-Increasing the concentration of a reactant -Grinding a large piece of solid reactant into a fine powder
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?
-Intermediate concentrations are expressed in terms of reactant concentrations using rate laws for the fast steps. -The overall rate law will reflect the concentrations of any reactants involved in all steps up to and including the rate-determining step.
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 statements correctly describe the average rate of a reaction?
-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]initial/ tfinal−tinitial
Which of the following criteria must be met for a reaction mechanism to be considered valid?
-The elementary steps must add up to the overall balanced reaction. -The rate law for the rate-determining step must correlate with the experimentally determined rate law.
Which of the following are described by a reaction mechanism?
-The identities of any reaction intermediates -The sequence of individual steps that make up the reaction -An explanation of the way in which the individual reactants are transformed to products
Select all the statements that correctly describe the instantaneous reaction rate.
-The instantaneous reaction rate is proportional to reactant concentration. -Instantaneous rate is calculated by finding the slope of a tangent to the curve of concentration versus time at any point on the curve.
Which of the following factors are affected by an increase in reactant concentration?
-The number of reactant collisions -The number of reactant particles in a given volume -The rate of reaction
rate = k[Br-][BrO3-][H+]2 rate = k[O3]2[O2]-1 rate = k[NO]2[O2] rate = k[NH3]0
-The overall reaction order is four. -The overall reaction order is one. -The rate is first order with respect to O2. -The rate is not dependent on the reactant concentration.
Which of the following statements correctly describe the rate constant k for a reaction?
-The rate constant has a constant value for a given reaction at a constant temperature. -The rate constant relates reaction rate to reactant concentration.
The order of a reaction and its rate constant can be determined graphically. Select all the statements that correctly describe this process.
-The rate constant is related to the slope of the straight line obtained.-The function of [A] versus time that gives a straight line plot indicates the reaction order.
Which of the following statements correctly describe a rate law for a reaction?
-The rate law includes the rate constant for the reaction. -The rate law relates the rate of reaction to the concentrations of the reactants.
Select all the statements that correctly describe the rate-determining step in any reaction.
-The rate-determining step is an elementary step. -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.
Select all the statements that describe an integrated rate law.
-The reactant concentration at any time in the reaction can be determined from the integrated rate law. -The value of the reaction constant, k, can be determined using an integrated rate law. -An integrated rate law includes time as a variable.
Which of the following statements correctly describe the straight-line plot obtained from concentration and time data for the first-order reaction A → products?
-The straight line is obtained by plotting ln[A] versus time.-The slope of the line is negative.-The rate constant for the reaction is related to the slope of the straight line.
Which of the following statements correctly describe the transition state of a reaction?
-The transition state only exists at the instant of highest potential energy in the reaction. -The transition state species is highly unstable.
Which of the following statements correctly describe how a rate law is determined?
-The value of k can be calculated from a single experiment once the reaction orders are known. -The rate law is determined by measuring the initial reaction rate for different reactant concentrations. -If there is more than one reactant present the reaction orders will usually be determined individually.
Which of the following factors will influence the rate of a chemical reaction?
-reaction temperature -surface area of a solid reactant -reactant concentration
The reaction AB (g) → A (g) + B (g) follows second-order kinetics. If k = 0.200 L/mol⋅s and [AB]0 = 1.50 M, what is the concentration of AB after 10.0 s?
0.375 M
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 the equation of each fast step preceding the rate-determining step as an equilibrium process. 2. Write the rate laws for the forward and reverse processes for each fast step that precedes the rate-determining step. 3. Use the rate laws derived for the fast steps to express the concentrations of any intermediates in terms of reactant concentrations 4. Derive the overall rate law by substituting expressions for intermediate concentrations into the rate law for the rate-determining step.
Calculate the activation energy for the reaction 2NOCl (g) → 2NO (g) + Cl2 (g), if the rate constant k is equal to 0.286 L/mol⋅s at 500. K and 0.175 L/mol⋅s at 490. K.
1.00 × 10^2 kJ/mol
Which of the following plots will give a straight line for a reaction that follows second-order kinetics? The reaction is represented by A → products.
1/[A] versus time
Which of the following options gives the correct expression for the integrated rate law for a reaction that follows second-order kinetics? The reactant is represented by the equation A → products.
1/[A]t = kt + 1/[A]0
At 25°C, HI breaks down very slowly to form H2H2 and I2I2. The reaction follows second-order kinetics and k at 25°C is 2.4 × 10−21 L/mol·s2.4 × 10-21 L/mol·s. If 0.0100 mol of HI(g) is placed in a 1.0-L container, how long will it take for the concentration of HI to reach 0.00900 mol/L?
4.6 x 10 ^21 s
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
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
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.
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
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
True or false: Based on the balanced equation N2 (g) + 3H2 (g) → 2NH3 (g), the rate law is given by rate = k[N2][H2]3.
FALSE
Which of the following attributes are characteristic of enzymes?
High specificity High rates of activity
Which question(s) can be answered from an integrated rate law that cannot be answered by other forms of the rate law? Select all that apply.
How long will it take to use up x moles per liter of A? What is [A] after y minutes of the reaction?
Which of the following the statements correctly relate experimental observations with reaction order?
If [A] is doubled and the reaction rate increases by a factor of 4, the reaction is second order with respect to A. If [A] is decreased to one-half of its original value and the reaction rate is halved, the reaction is first order with respect to A.
Which of the following options correctly interpret the rate law rate = k[H2][NO]2?
If [NO] is doubled while [H2] remains the same, the reaction will occur 4 times faster. The reaction is second order with respect to NO.
Reaction rate is expressed as a change in the _____ of reactants or products as a function of ____
concentration; time
H2O2 (aq)H2O2 (aq) decomposes rapidly in the presence of iodide ion (I−I-). Select all the statements that correctly interpret the experimental data provided for this reaction.
Rate = k[H2O2][I−]kH2O2I- The reaction is first order with respect to I−I-.
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
Match each point on the energy profile shown with the correct description.
a= transition-state energy b= activation energy c =energy of reactants d =energy of products
Select all the options that correctly describe the straight-line plot obtained for rate constant and temperature data.
The activation energy for the reaction can be determined from the slope. The values plotted on the x axis are given by 1T1T where T is the absolute temperature.
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 average rate, instantaneous rate, and initial rate?
The initial rate is an instantaneous rate at t = 0. The average rate is an average of instantaneous rates for a given period of time.
What is molecularity?
The number of reactant particles that react in an elementary step
Select all the statements that correctly interpret the experimental data provided for the reaction 2Mg (s) + O2 (g) → MgO (s).
The overall reaction order is 3. The reaction is second order with respect to [O2]. The reaction is first order with respect to Mg.
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.
Reaction rates are expressed as the change in _____ over a period of _______
concentration; time
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) _____ complex or ______ state.
activated, transition
The _____ energy of a reaction is the energy threshold that colliding molecules must exceed in order to react.
activation
Average rate vs instantaneous rate vs initial rate
average: The slope of a line joining two points on a curve instantaneous: The slope of a line tangent to the curve at a particular point Initial: The slope of a line tangent to the curve at t = 0
What is an elementary reaction?
each step that makes up a reaction mechanism
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, orientation
A(n) ______ is a protein that acts as a biological catalyst.
enzyme
If the rate doubles when [A] doubles, the reaction is If the rate quadruples when [A] doubles, the reaction is If the rate does not change when [A] doubles, the reaction is
first order with respect to A second order with respect to A zero order with respect to A
The use of finely powdered palladium metal to catalyze the reaction shown below is an example of ______ catalysis. C6H12 (l) + H2 (g) → C6H14 (l)
heterogenous
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)
homogenous
The Arrhenius equation shows that the rate constant for a reaction (k) _____ when temperature increases and _____ when activation energy increases.
increases, decreases
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
Select all the options that correctly identify the components of the Arrhenius equation (given).
k is the rate constant for the reaction. T is the temperature in K. Ea is the activation energy for the reaction.
k x, y [A], [B] values????
k= rate constant x,y = reaction orders A, B= reactant concentrations
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 _____ energy is greater.
kinetic, activation
When two molecules in motion collide, ______ energy is partially converted to ______ energy; this may result in the breaking of bonds.
kinetic; vibrational
Kinetic data are often analyzed graphically. Depending on the reaction order, a function of [A] is plotted versus time to obtain a straight _____ plot. The value of the rate constant is determined from the _____ of the plot.
line; slope
The decomposition of N2O to form N2 and O2 is a first-order reaction. The rate constant for the reaction is 1.94 × 10-4 min-1 at 730°C. If [A]0 is 0.25 M, how much time is required for [A] to drop to 0.10 M?
ln 0.10/0.25 = - (1.94 × 10-4)tt = 0.916/1.94×10^−4= 4720 min
In a particular first-order reaction, [A] drops to 35.5% of its initial value in 4.90 min at 25°C. Select all the options that correctly reflect the steps required to solve for the rate constant, k.
ln(0.355) = - k(4.90 min)ln[A]t[A]0 = ln(0.355)
The rate constant for a particular reaction at 215°C is equal to 5.0 × 10-3 s-1 and its activation energy is 39.4 kJ/mol. Select all the options that correctly reflect the steps required to calculate the rate constant at 452°C.
ln5.0×10−3k25.0×10-3k2 = -3.18 5.0×10−3k25.0×10-3k2 = 0.042
Select all the options that correctly reflect the integrated rate law for a first-order reaction.
ln[A]t = -kt + ln[A]0 ln[A]t/[A]0[A]t = -kt
Which of the following gives the correct expression for the Arrhenius equation using two different temperature values?
lnk1k2k1k2 = EaREaR(1T2 - 1T1)
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
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
An energy profile for a reaction plots ______ energy versus reaction ______.
potential; progress
Chemical kinetics studies the ____ of chemical reactions, how fast reactants are converted into products.
rate
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 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
The ______ step in any reaction sequence determines the rate law for the overall reaction. This step is called the rate- ________ step
slowest , determining
For a proposed reaction mechanism to be valid, the rate law determined from experimental data must match the rate law for the _____
slowest reacting step
An enzyme binds to a reactant, which is called the _______, at the ______ site of the enzyme.
substrate; 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
The dimerization of butadiene proceeds according to second-order kinetics. If the rate constant at a particular temperature is 0.100 M-1 ⋅ min-1, calculate the half-life for an initial reactant concentration of 0.35 M.
t 1/2= 29 min t 1/2= 1/ k (A) 0 = 1/ 0.100 x 0.35 =29 min
Match the equation for half-life with the appropriate reaction order.
t1/2 = 0.693/k First-order reaction t1/2 = 1/k[A]0 Second-order reaction t1/2 = [A]0/2k Zeroth-order reaction
The decomposition of NO2 (g) proceeds according to the reaction below: 2NO2 (g) → 2NO (g) + O2 (g) The rate law for this reaction is rate = k[NO2]2. Using the data shown, calculate the value of k, as well as the half-life for the initial concentration given
t1/2 = 2.0 s k = 2.5 s-1 ⋅ M-1
Match the effect of initial [reactant] on half-life with the appropriate reaction order.
t1/2 does not depend on initial [reactant]. matches =First-order reaction t1/2 is inversely proportional to initial [reactant]. = Second-order reaction t1/2 is directly proportional to initial [reactant].= Zeroth-order reaction
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
tangent; decreases
Match each change given to the effect it will have on the value of k, the rate constant for a reaction.
temperature increases = k increases Ea increases = k decreases
The Arrhenius equation relates the rate constant of a reaction to ______. Select all the options that would complete this sentence correctly.
the activation energy the absolute temperature the frequency of collisions between particles
