Deck 7: Kinetics

Question 1

If the rate of a reaction increases by a factor of 64 when the concentration of reactant increases by a factor of 4, the order of the reaction with respect to this reactant is

A) 16.
B) 2.
C) 4.
D) 1.
E) 3.

Answer 1

E

Question 2

If the average rate of formation of H₂(g) is 3.90 (mol H₂).L^-1.s^-1 for the reaction2PH₃(g) $\rightarrow$ 2P(g)+ 3H₂(g),The unique average reaction rate is

A) 3.90 mol.L^-1.s^-1.
B) 1.30 mol.L^-1.s^-1.
C) 2.60 mol.L^-1.s^-1.
D) 7.80 mol.L^-1.s^-1.
E) 11.7 mol.L^-1.s^-1.

Answer 2

1.30 mol.L^-1.s^-1.

Question 3

For a given first-order reaction, after 2.00 min,20% of the reactants remain.Calculate the rate constant for the reaction.

A) 0.0134 s^-1
B) 0.000808 s^-1
C) 74.6 s^-1
D) 0.00582 s^-1
E) 0.00186 s^-1

Answer 3

0.0134 s^-1

Question 4

Given:
2A(g)+ B(g) $\rightarrow$ C(g)+ D(g)
When [A] = [B] = 0.10 M,The rate is 2.0 M.s^-1; for [A] = [B] = 0.20,The rate is 8.0 M.s^-1; and for[A] = 0.10 M,[B] = 0.20 M,The rate is 2.0 M.s^-1.The rate law is

A) rate = k[A].
B) rate = k[B]².
C) rate = k[A][B]⁰.
D) rate = k[A][B].
E) rate = k[A]².

Question 5

The concentration.time dependence for a first-order reaction is:
At which point on the curve is the reaction fastest?

A) A
B) B
C) C
D) A + t_½
E) The rates are the same at all points.

Question 6

The concentration-time dependence is shown below for two first-order reactions is:
Which reaction has the larger rate constant?

Question 7

The concentration-time dependence for two first order reactions is:
Which reaction has the greater t_½?

Question 8

The reaction
2NO(g)+ 2H₂(g) $\rightarrow$ N₂(g)+ 2H₂O(g)
Is first order in H₂ and second order in NO.Starting with equal concentrations of H₂ and NO,The rate after 25% of the H₂ has reacted is what percent of the initial rate?

A) 75.0%
B) 42.2%
C) 6.25%
D) 56.3%
E) 1.56%

Question 9

Given:
2O₃(g) $\rightarrow$ 3O₂(g)
Rate = k[O₃]²[O₂]^-1
The overall order of the reaction and the order with respect to [O₃] are

A) -1 and 3.
B) 1 and 2.
C) 0 and 1.
D) 2 and 2.
E) 3 and 2.

Question 10

It is important to distinguish between the reaction rate and the rate constant.The units of reaction rate are M.s^-1.

Question 11

The reaction
2NO(g)+ 2H₂(g) $\rightarrow$ N₂(g)+ 2H₂O(g)
Is first order in H₂ and second order in NO.Starting with equal concentrations of H₂ and NO,The rate after 50% of the H₂ has reacted is what percent of the initial rate?

A) 18.8%
B) 37.5%
C) 25.0%
D) 50.0%
E) 12.5%

Question 12

If the average rate of decomposition of PH₃(g) is 3.2 (mol PH₃).L^-1.min^-1 for the reaction 2PH₃(g) $\rightarrow$ 2P(g)+ 3H₂(g),
The unique average reaction rate is

A) 3.2 mol.L^-1.min^-1.
B) 2.1 mol.L^-1.min^-1.
C) 1.6 mol.L^-1.min^-1.
D) 4.8 mol.L^-1.min^-1.
E) 6.4 mol.L^-1.min^-1.

Question 13

The concentration.time curves for two sets of reactions, A/B and C/D,
Are:
Which set of reactions has the largest rate constant?

Question 14

For the reaction S₂O₈2^-(aq) + 3I^-(aq) $\rightarrow$ 2SO₄2^-(aq)+ I₃-(aq),
Rate =k[S₂O₈2^-][I^-].When the reaction is followed under pseudo-first-order conditions with [S₂O₈2^-] = 200 m M and [I^-] = 1.5 m M,
The rate constant was 1.82 s^-1.The second order rate constant,K,For the reaction is

A) 1.21 * 10³ M^-1.s^-1.
B) 6.07 * 10³ M^-1.s^-1.
C) 9.10 M^-1.s^-1.
D) 1.37 * 10^-2 M^-1.s^-1.
E) 1.82 M^-1.s^-1..

Question 15

Given:
4Fe²⁺(aq)+ O₂(aq)+ 2H₂O(l) $\rightarrow$ 4Fe³⁺(aq)+ 4OH^-(aq)
Rate = k[Fe²⁺][OH^-]²[O₂]
The overall order of the reaction and the order with respect to O₂ are

A) 4 and 1.
B) 5 and 1.
C) 3 and 1.
D) 4 and 2.
E) 7 and 1.

Question 16

If the rate of reaction increases by a factor of 9.6 when the concentration of reactant increases by a factor of 3.1, the order of the reaction with respect to this reactant is

A) 1.5
B) 3
C) 4
D) 2
E) 1

Question 17

A first-order reaction has a rate constant of 0.00300 s^-1 .The time required for 60% reaction is

A) 153 s.
B) 73.9 s.
C) 170 s.
D) 133 s.
E) 305 s.

Question 18

The concentration-time curves for two sets of reactions, A/B and C/D,
Are:
Which of the reactions are first order?

A) B and D
B) A and B
C) C and D
D) A and C

Question 19

The rate of formation of oxygen in the reaction
2N₂O₅(g) $\rightarrow$ 4NO₂(g)+ O₂(g)Is 2.28 (mol O₂).L^-1.s^-1.What is the rate of formation of NO₂?

A) 0.57 (mol NO₂).L^-1.s^-1
B) 9.12 (mol NO₂).L^-1.s^-1
C) 2.28 (mol NO₂).L^-1.s^-1
D) 1.14 (mol NO₂).L^-1.s^-1
E) 4.56 (mol NO₂).L^-1.s^-1

Question 20

If the rate of reaction increases by a factor of 2.3 when the concentration of reactant increases by a factor of 1.5, the order of the reaction with respect to this reactant is

A) 2.
B) 1.
C) 1.5.
D) 4.
E) 3.

Question 21

Consider the reaction
2N₂O(g) $\rightarrow$ 2N₂(g)+ O₂(g)
Rate = k[N₂O]
Calculate the time required for the concentration of N₂O(g) To decrease from 0.75 M to 0.33 M.The rate constant for the reaction is k = 6.8 * 10^-3 s^-1.

A) 2.7 min
B) 1.7 min
C) 0.87 min
D) 0.92 min
E) 2.0 min

Question 22

Given: A $\rightarrow$ P rate = k[A]
If 20% of A reacts in 5.12 min,Calculate the time required for 90% of A to react.

A) 52.8 min
B) 1.05 min
C) 2.42 min
D) 3170 min
E) 22.9 min

Question 23

A first-order reaction has a half-life of 1.10 s .If the initial concentration of reactant is 0.384 M,How long will it take for the reactant concentration to reach 0.00100 M?

A) 9.45 s
B) 0.106 s
C) 4.10 s
D) 1.52 s
E) 0.244 s

Question 24

A nonsteroidal anti-inflammatory drug is metabolized with a first-order rate constant of 3.25day^-1 .What fraction of the drug remains in the body after 13.0 hr?

A) 0.172
B) 0.0174
C) 0.828
D) 0.873
E) 0.127

Question 25

Consider the reaction
2N₂O₅(g) $\rightarrow$ 4NO₂(g)+ O₂(g)
Rate = k[N₂O₅]
If the initial concentration of N₂O₅ is 0.80 M,The concentration after 5 half-lives is

A) 0.11 M.
B) 0.025 M.
C) 0.032 M.
D) 0.16 M.
E) 0.050 M.

Question 26

The reaction
2ClO₂(g)+ F₂(g) $\rightarrow$ 2FClO₂(g)
Is first order in both ClO₂ and F₂.When the initial concentrations of ClO₂ and F₂ are equal,The rate after 25% of the F₂ has reacted is what percent of the initial rate?

A) 75.0%
B) 18.8%
C) 37.5%
D) 28.1%
E) 12.5%

Question 27

What is the half-life of a reaction that has a rate constant of 280 s^-1?

A) 194 s
B) 3.6 ms
C) 404 ms
D) Because the concentration of reactant is not given, the calculation cannot be performed.
E) 2.5 ms

Question 28

The rates of first-order and second-order reactions do not change with elapsed time

Question 29

For the reaction cyclopropane(g) $\rightarrow$ propene(g)at 500 ^$\omicron$ C,a plot of ln[cyclopropane] vs t gives a straight line with a slope of -0.00067 s^-1.What is the order of this reaction and what is the rate constant?

Question 30

For the reaction
Cyclopropane $\rightarrow$ propene
A plot of ln[cyclopropane] vs time in seconds gives a straight line with slope -4.1 * 10^-3 s^-1 at 550 ^$\omicron$ C.What is the rate constant for this reaction?

A) 3.9 * 10^-2 s^-1
B) 8.2 * 10^-3 s^-1
C) 4.1 * 10^-3 s^-1
D) 1.8 * 10^-3 s^-1
E) 2.1 * 10^-3 s^-1

Question 31

For the reaction cyclobutane(g) $\rightarrow$ 2ethylene(g)At 800 K,A plot of ln[cyclobutane] vs t gives a straight line with a slope of -1.6 s^-1.Calculate the time needed for the concentration of cyclobutane to fall to 1/16 of its initial value.

A) 2.3 s
B) 1.7 s
C) 1.3 s
D) 0.63 s
E) 1.6 s

Question 32

For the reaction A $\rightarrow$ products,the following data were collected. $$\begin{array} { | l | l | l | l | l | l | } \hline \text { time, s } & 0 & 1 & 2 & 3 & 4 \\\hline [ \mathrm { A } ] . \mathrm { M } & 1.00 & 0.430 & 0.270 & 0.200 & 0.160 \\\hline\end{array}$$
Determine the order of the reaction and calculate the rate constant.

Question 33

For a second-order reaction, a straight line is obtained from a plot of

A) 1/[A] vs t.
B) ln(1/t) vs [A].
C) [A] vs t.
D) ln[A] vs t.
E) ln(t) vs [A].

Question 34

A given first-order reaction has a rate constant of 0.00300 s^-1 .The time required for 85% reaction is

A) 632 s.
B) 23.5 s.
C) 275 s.
D) 316 s.
E) 54.2 s.

Question 35

Consider the reaction
2N₂O₅(g) $\rightarrow$ 4NO₂(g)+ O₂(g)
Rate = k[N₂O₅]
Calculate the time for the concentration of N₂O₅ to fall to one-fourth its initial value if the half-life is 133 s.

A) 133 s
B) 33.3 s
C) 266 s
D) 66.6 s
E) 533 s

Question 36

What is the rate constant for a first-order reaction with a half-life of 9.0 ms?

A) 13 s^-1
B) 77 s^-1
C) 9.0 s^-1
D) 6.2 s^-1
E) 0.11 s^-1

Question 37

A given compound decomposes with a half-life of 8.0 s and the half-life is independent of the concentration .How long does it take for the concentration to decrease to one-ninth of its initial value?

A) 32 s
B) 25 s
C) 72 s
D) 64 s
E) 3.6 s

Question 38

Technetium-99m, used to image the heart and brain,Has a half-life of 6.00 h.
What fraction of technetium-99m remains in the body after 1 day?

A) 0.0625
B) 0.250
C) 0.0313
D) 0.125

Question 39

Consider the reaction
2N₂O(g) $\rightarrow$ 2N₂(g)+ O₂(g)
Rate = k[N₂O]For an initial concentration of N₂O of 0.50 M,What is the concentration of N₂O remaining after 2.0 min if k = 3.4 * 10^-3 s^-1?

A) 0.50 M
B) 0.55 M
C) 0.66 M
D) 0.33 M
E) 0.17 M

Question 40

For a given first-order reaction, after 230 s, 33% of the reactants remain.Calculate the rate constant for the reaction.

A) 207 s^-1
B) 0.00174 s^-1
C) 0.00209 s^-1
D) 0.000756 s^-1
E) 0.00482 s^-1

Question 41

The reaction profile for the reaction
[(CN)₅CoOH₂]^2-(aq)+ SCN^-(aq) $\rightarrow$ [(CN)₅CoSCN]^3- + H₂O(l)
is
Identify the structure of B.What do A and C represent?

Question 42

A catalyst facilitates a reaction by

A) increasing the activation energy for the reverse reaction.
B) lowering the activation energy of the reaction.
C) shifting the position of the equilibrium of the reaction.
D) decreasing the temperature at which the reaction will proceed spontaneously.
E) making the reaction more exothermic.

Question 43

The activation energy of a reaction is given by

A) +(slope of a plot of lnk vs 1/T) / R.
B) -(slope of a plot of lnk vs 1/T) / R.
C) -R / (slope of a plot of lnk vs 1/T).
D) +(slope of a plot of lnk vs 1/T) * R.
E) -(slope of a plot of lnk vs 1/T) * R.

Question 44

The reaction [(CN)₅CoOH₂]^2-(aq)+ SCN^-(aq) $\rightarrow$ [(CN)₅CoSCN]^3-+ H₂O(l)
has the rate law,rate=k[(CN)₅CoOH₂2^-].Postulate a mechanism for this reaction.

Question 45

Consider the dimerization reaction below:
2A $\rightarrow$ A₂
Rate = k[A]²
When the initial concentration of A is 2.0 M,It requires 30 min for 60% of A to react. Calculate the rate constant.

A) 1.1 * 10^-3 M^-1.s^-1
B) 3.2 * 10^-3 M^-1.s^-1
C) 5.0 * 10^-4 M^-1.s^-1
D) 1.9 * 10^-4 M^-1.s^-1
E) 4.2 * 10^-4 M^-1.s^-1

Question 46

Consider the reaction for the dimerization of butadiene(g)at a certain temperature.
2C₄H₆(g) $\rightarrow$ C₈H₁₂(g)
rate = k[C₄H₆]².When the initial concentration of butadiene is 0.500 M,
the time required for 80% dimerization is measured at 11.4 s.What is the rate constant for the dimerization?

Question 47

A reaction that has a very low activation energy

A) has a rate that is very sensitive to temperature.
B) has a rate that does not change much with temperature.
C) must be second order.
D) gives a curved Arrhenius plot.
E) must be first order.

Question 48

A possible mechanism for the reaction 2NO(g) + O₂(g) $\rightarrow$ 2NO₂(g)
Is:
2NO(g)
$f$
N₂O₂(g)
K₁,K₁',Fast
N₂O₂(g)+ O₂(g) $\rightarrow$ 2NO₂(g)
K₂,Slow
Application of the steady-state approximation gives

A) [N₂O₂] = 0.
B) k₁[NO]² - k₂[N₂O₂][O₂] = 0.
C) [N₂O₂] = (k₁/k₂)[NO]².
D) k₁[NO]² - k₁'[N₂O₂] -k₂[N₂O₂][O₂] = 0.
E) [N₂O₂] = (k₁/k₁')[NO]².

Question 49

The rate law for the following mechanism is
NO₂(g)+ F₂(g) $\rightarrow$ NO₂F(g)+ F(g)
K₁,
Slow
F(g)+ NO₂(g) $\rightarrow$ NO₂F(g)
K₂,
Fast

A) rate = k₂[NO₂]².
B) rate = k₂[NO₂][F].
C) rate = k₁[NO₂][F₂].
D) rate = k₁k₂[NO₂]².
E) rate = k₁[NO₂F][F].

Question 50

The reaction between nitrogen dioxide and carbon monoxide is thought to occur by the mechanism
2NO₂(g $\rightarrow$ NO₃(g)+ NO(g)
K₁,Slow
NO₃(g)+ CO(g) $\rightarrow$ NO₂(g)+ CO₂(g)
K₂,Fast
The rate law for this mechanism is

A) rate = k₁k₂[NO₂]²[CO].
B) rate = (k₁/k₂)[NO₂]²[CO].
C) rate = k₁[NO₃][NO].
D) rate = k₂[NO₃][CO].
E) rate = k₁[NO₂]².

Question 51

A certain reaction has a rate constant of 8.8 s^-1 at 298 K and 140 s^-1 at 323 K .What is the activation energy for this reaction?

A) 38 kJ.mol^-1
B) 89 kJ.mol^-1
C) 120 kJ.mol^-1
D) 23 kJ.mol^-1
E) 1.2 kJ.mol^-1

Question 52

A second-order reaction has a rate constant of 1.25 M^-1.s^-1 .If the initial reactant concentration is 1.0 M,Calculate the time required for 90% reaction.

A) 1.3 s
B) 7.2 s
C) 0.13 s
D) 17 s
E) 0.89 s

Question 53

For the reaction cyclobutane(g) $\rightarrow$ 2ethylene(g)
At 800 K,The half-life is 0.43 s.Calculate the time needed for the concentration of cyclobutane to fall to 1/64 of its initial value.

A) 2.2 s
B) 2.6 s
C) 16 ms
D) 0.38 s
E) 0.43 s

Question 54

Consider the reaction
NOBr(g) $\rightarrow$ NO(g)+ ½Br₂(g)
A plot of [NOBr]^-sup>1 vs t gives a straight line with a slope of 2.00 M^-1.s^-1.The order of the reaction and the rate constant,Respectively,Are

A) second-order and 0.500 M^-1.s^-1.
B) first-order and 2.00 s^-1.
C) second-order and 2.00 M^-1.s^-1
D) first-order and 0.241 s^-1.
E) second-order and 16.6 M^-1.s^-1

Question 55

What is the half-life of a second order reaction?

Question 56

For the reaction
HO(g)+ H₂(g) $\rightarrow$ H₂O(g)+ H(g)
A plot of
$\ln k$
Versus 1/T gives a straight line with a slope equal to -5.1 * 10³ K.What is the activation energy for the reaction?

A) 42 kJ.mol^-1
B) 98 kJ.mol^-1
C) 0.61 kJ.mol^-1
D) 5.1 kJ.mol^-1
E) 12 kJ.mol^-1

Question 57

Given:
CH₄(g)+ Cl₂(g) $\rightarrow$ CH₃Cl(g)+ HCl(g)
The rate law for this elementary process is

A) rate = k[Cl₂].
B) k[CH₃Cl][HCl].
C) rate = k[CH₄][Cl₂].
D) rate = k[CH₄].
E) rate = k[CH₄]².

Question 58

An elementary process has an activation energy of 92 kJ/mol .If the enthalpy change for the reaction is -62 kJ/mol, What is the activation energy for the reverse reaction?

A) 154 kJ/mol
B) 62 kJ/mol
C) 92 kJ/mol
D) 30 kJ/mol

Question 59

The rate law for the following mechanism is
ClO^-(aq)+ H₂O(l) $f$
HOCl(aq)+ OH^-(aq)
K,Fast
I^-(aq)+ HOCl(aq) $\rightarrow$ HOI(aq)+ Cl^-(aq)
K₁,Slow
HOI(aq)+ OH^-(aq) $\rightarrow$ OI^-(aq)+ H₂O(l)
K₂,Fast

A) rate = k₁[I^-][HOCl].
B) rate = k₁K[ClO^-][I^-][OH^-].
C) rate = k₁K[ClO^-][I^-][OH^-]^-1.
D) rate = k₁k₂K[ClO^-][I^-].
E) rate = k₁K[ClO^-][I^-].

Question 60

A reaction has k = 8.39 M^-1.s^-1 .How long does it take for the reactant concentration to drop from 0.0840 M to 0.0220 M?

A) 5.42 s
B) 2.00 s
C) 1.42 s
D) 8.39 s
E) 4.00 s

Question 61

For the elementary reaction A + 2B $\rightarrow$ products, rate = k[A][B].

Question 62

For the reaction A $\rightarrow$ products, the following data were collected. $$\begin{array} { | l | l | l | l | l | l | } \hline \text { time,s } & 0 & 1.00 & 2.00 & 3.00 & 4.00 \\\hline [ A ] \mathrm { A } , \mathrm { M } & 1.00 & 0.430 & 0.270 & 0.200 & 0.160 \\\hline\end{array}$$
The half-life for this reaction is

A) 0.521 s
B) 0.752 s
C) 0.922 s
D) 1.08 s

Question 63

Consider the reaction
A + B $\rightarrow$ C + D rate = k[A]²
The time it takes for [A] to decrease from 1.0 to 0.50 M is the same as the time it takes for [A] to decrease from0.50 to 0.25 M.

Question 64

Consider the following mechanism for the destruction of ozone.
O₃ + NO $\rarr$ NO₂ + O₂
NO₂ + O $\rarr$ NO + O₂
What is the catalyst in this reaction?

Question 65

The HBr synthesis is thought to involve the following reactions:
1.Br₂ $\rightarrow$ 2Br.
2.Br. + H₂ $\rightarrow$ HBr + H.
3.H. + Br₂ $\rightarrow$ HBr + Br.
4.2Br. $\rightarrow$ Br₂
5.2H. $\rightarrow$ H₂
6.H. + Br. $\rightarrow$ HBr
The chain propagation reactions in this mechanism are reactions"

A) 6.
B) 1, 2, 3, and 6.
C) 2 and 3.
D) 1, 2, and 3.
E) 2, 3, and 6.

Question 66

The reaction
3C + D $\rightarrow$ products
Has rate = k[D] and has a half-life of 1.29 s.If initially [D] = 0.820,What is the concentration of D after 2.55 s?

A) 0.21
B) 0.12
C) 0.56
D) 0.28
E) 0.41

Question 67

Consider the reaction
2A $\rightarrow$ B,Rate = k[A]²
If the rate of disappearance of A is followed,derive the experimental rate constant.

Question 68

For a zero-order reaction,the rate constant has the same units as the rate of reaction.

Question 69

The HBr synthesis is thought to involve the following reactions:
1.Br₂ $\rightarrow$ 2Br.
2.Br. + H₂ $\rightarrow$ HBr + H.
3.H. + Br₂ $\rightarrow$ HBr + Br.
4.2Br. $\rightarrow$ Br₂
5.2H. $\rightarrow$ H₂
6.H. + Br. $\rightarrow$ HBr
The chain termination reactions in this mechanism are reactions"

A) 3, 4, and 5.
B) 4 and 5.
C) 4, 5, and 6.
D) 6.
E) 3 and 4.

Question 70

Given:
5Br^-(aq)+ BrO₃^-(aq)+ 6H⁺(aq) $\rightarrow$ 3Br₂(aq)+ 3H₂O(l)
Rate = k[Br^-][ BrO₃^-][H⁺]²
The overall order of the reaction and the order with respect to H⁺ are

A) 4 and 2.
B) 5 and 6.
C) 3 and 2.
D) 5 and 2.
E) 6 and 2.

Question 71

The reaction 2A + B $\rightarrow$ D + E has the rate law,rate = a[A]²[B]/(b + c[A]) where a,b,and c are constants.The following mechanism has been proposed for this reaction.
A + B
k₁,k_-1
$f$
I
I + A $\rightarrow$ D + E
k₂
I is an unstable intermediate present in minute concentrations.Show that this mechanism leads to the observed rate law and evaluate the constantsa,b,and c in terms of the rate constants k₁,k_-1,and k₂.

Question 72

In the Michaelis-Menten mechanism of enzyme reaction, the Michaelis constant,K_M,Is

A) K_M = k₁/k₂.
B) K_M = k₁'/k₂.
C) K_M = (k₁' + k₂)/k₁.
D) K_M = k₁' + k₂.
E) K_M = k₁/k₁'.

Question 73

Given: A + B $\rightarrow$ P rate = k[A][B]
Which of the following is true?

A) k = ln 2/t_1/2
B) ln [A]_t = -kt + ln [A]_o
C) [A]_t = [A]_o/(1 + kt[A]_o)
D) 1/[A]_t = 1/kt

Question 74

The rate law for a reaction can be determined from the coefficients in the overall reaction.

Question 75

The reaction profile for the mechanism
NO₂(g)+ F₂(g) $\rightarrow$ NO₂F(g)+ F(g)
Slow
F(g)+ NO₂(g) $\rightarrow$ NO₂F(g)
Fast
Shows

A) two maxima, the first maximum being the higher.
B) two maxima, the second maximum being the higher.
C) one maximum for the second step.
D) two maxima, both the same height.

Question 76

Consider the following mechanism for the production of phosgene.
Cl₂ $\rightarrow$ Cl + Cl
Cl + CO $\rightarrow$ COCl
COCl + Cl $\rightarrow$ COCl₂
The molecularity of the first and second elementary reactions is ____ and ____.

Question 77

The fraction of molecules that collide with a kinetic energy equal to the activation energy for a reaction decreases rapidly with an increase in temperature.

Question 78

The reaction 2NO(g) + O₂(g) $\rightarrow$ 2NO₂(g) Has $\Delta$ H_r ^$\omicron$ = -4 kJ.mol^-1.
A possible mechanism for this reaction is
2NO(g) Rapid equilibrium,K
$f$
N₂O₂(g)
N₂O₂(g)+O₂(g) $\rightarrow$ 2NO₂(g)
Slow,K
If the activation energy for the reverse reaction is 225 kJ.mol^-1.
What is the activation energy for the forward reaction?

A) Because an intermediate is involved, the forward activation energy cannot be calculated with the given information.
B) 111 kJ.mol^-1.
C) 339 kJ.mol^-1.
D) 114 kJ.mol^-1.
E) 55.5 kJ.mol^-1.

Question 79

A possible mechanism for the reaction A + B + D $\rightarrow$ E + F is
A + B
k₁,k_-1,fast
$f$
C
C + D $\rightarrow$ E + F
k₂
where C is a reactive intermediate present in very low concentrations.
Calculate the steady state concentration of C in terms of the rate constants for the individual steps and the concentrations of the reactants.

Question 80

The reduction of M³⁺ by Cr²⁺ was studied with [Cr²⁺] 100 times the concentration of Cr²⁺ .When [Cr²⁺] = 0.0050 M,The rate was 2.5 s^-1.The rate constant for this reaction is

A) 1.3 M^-1·s^-1
B) 0.013 M^-1·s^-1
C) 5.0 M^-1·s^-1
D) 500 M^-1·s^-1