Chapter 19 Chem 2
The reaction AB(g)-->A(g)+B(g) follows second-order kinetics. If k=0.200 L/mol*s and [AB]0=1.50M, what is the concentration of AB after 10.0s
0.375M
Correctly order the steps required to derive the overall rate law for a multistep reaction that has one or more fast initial steps
1. Express the equation of each fast step preceding the rate-determine 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 an overall rate law by substituting expressions for intermediate concentrations into the rate law for the rate determining step
For the reaction aA+bB-->cC+dD, the rate law is Rate = k[A]x[By] Match the appropriate definition with each term of the rate law
k - rate constant x,y - reaction orders [A],[B] - reactant concentrations
Match each rate law with the statement that correctly describes it
rate = k[Br][BrO3][H+]^2 - The overall reaction order is four rate = k[O3]^2[O2]^1 - The overall reaction order is one rate = k[NO]^2[O2] - The rate is first order with respect to O2 rate = k[NH3]^0 - The rate is not dependent on the reactant concentration
Match the effect of initial [reactant] on half=life with the appropriate reaction order
t1/2 does not depend on initial reactant - 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
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 - E/R Intercept - ln A
The rate constant for a particular reaction at 215C is equal to 5.0*10^-3s^-1 and its activation energy is 39.4kJ/mol. Select all the options that correctly reflect the steps required to calculate the rate constant at 452C
5.0*10^-3/k2 = 0.042 ln5.0*10^-3/k2 = -3.18
Which of the following statements best describes the effect of reactant concentration on reaction rate
A reactant concentration increases the number of reaction collisions increases, which in turn increases the reaction rate
Every chemical reaction proceeds through a high-energy unstable species as reactants are converted to products and bonds are in the process being formed 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
Match the type of reaction rate with the correct point on a graph of [reactant] versus time
Average Rate - The slope of a line joining two points on a curve Instantaneous Rate - The slope of a line tangent to the curve at a particular point Initial Rate - The slope of a line tangent to the curve at t=0
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
What is an elementary step
Each step that makes up a reaction mechanism
True or False Based on the balanced equation N2(g)+3H2(g)-->2NH3(g) The rate law is given rate = k[N2][H2]3
False
Match the order of the reaction with the information provided about the effect of changing [A] for the reaction A--> products
First Order - The reaction doubles when the amount of [A] is doubled Second Order - The reaction quadruples when the amount of [A] is doubled Zero Order - The reaction does not change when the amount of [A] is doubled
Consider the reaction 2H2(g)+O2(g)-->2H2O(g) At a particular moment in the reaction, H2(g) is disappearing at a rate of 0.024M/s Select the statements that correctly describe this reaction
H2O(g) is being formed at a rate of 0.024M/s O2(g) is being used up at a rate of 0.012M/s
The - - of a reaction is the time required for the reactant concentration to reach half its initial value
Half-life
Match each type of catalyst to the correct description
Homogeneous catalyst - Reactants and catalyst are dispersed in a single phase Heterogeneous catalyst - Reactants and catalyst are in different phases Enzyme - A biological catalyst
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 1. NO(g)+Br(g)-->NOBr2(g) Fast 2. NOBr2(g)+NO(g)-->2NOBr(g) Slow
NO Br2
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
Identify the reaction intermediate(s) in the reaction mechanism shown
(CH3)3C+ (CH3)3C-OH2+
Chemical kinetics studies the - of chemical reactions, i.e., how fast reactants are converted into products
Rate
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
NO(g) reacts with H2(g) according to the following balanced equation 2NO(g)+2H(g)-->N2(g)+2H2O(g) Which of the following overall rate laws is consistent with the proposed mechanism shown
Rate = k[H2][NO]^2
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 reaction-step
Using a plot of [reactant] versus time, the instantaneous reaction rate is calculatedly finding the slope of a(n) - to the curve at any particular time. Instantaneous rate - as [reactant] decreases
Tangent Decreases
What is the molecularity of the elementary step A(g)+B(g)+C(g)-->D(g)
Telemolecular
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
Select the statements that correctly describe the kinetics of an elementary reaction
The elementary reaction 2HI(g)-->H2(g)+I2(g) follows second-order kinetics The rate law for an elementary step can be deduced from its balanced chemical equation For an elementary reaction, reaction order equals molecularity
A chemical reaction cars 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
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
A first-order reaction has a half-life of 4.1 minutes. The percentage of reactant remaining after 20 minutes is approximately equal to -
3.1%
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
An elementary step is characterized by its - which is equal to the number of reactant particles in the step
Molecularity
Which of the following can be calculated using the two-point form of the Arrhenius equation (given)? ln K1/k2 = Ea/R (1/T1 - 1/T2)
The rate constant at different temperatures The activation energy of the reaction
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 rate constant for the reaction is related to the slope of the straight line The straight line is obtained by plotting ln[A] versus time The slope of the line is negative
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]
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
Match each point of the energy profile with the correct description
a - Transition state energy b - Activation energy c - Energy of reactants d - Energy of products
