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Date	November 2020	Marks available	1	Reference code	20N.1.hl.TZ0.20
Level	HL	Paper	1	Time zone	TZ0
Command term	Deduce	Question number	20	Adapted from	N/A

Question

What are the units of the rate constant, $k$ , if the rate equation is $Rate = k [A] {[B]}^{2}$ ?

A. $mol {dm}^{- 3} s^{- 1}$

B. ${dm}^{3} {mol}^{- 1} s^{- 1}$

C. ${dm}^{6} {mol}^{- 2} s^{- 1}$

D. ${dm}^{9} {mol}^{- 3} s^{- 1}$

Markscheme

Examiners report

Nearly three quarters of candidates could identify the units of a rate constant for a 3rd order reaction.

Syllabus sections

Additional higher level (AHL) » Topic 16: Chemical kinetics » 16.1 Rate expression and reaction mechanism

Show 63 related questions

17N.2.hl.TZ0.2e.iii: Calculate the value of the rate constant at 263 K.
22M.2.hl.TZ1.2c(i):
Use the graph to deduce the dependence of the reaction rate on the amount of Mg.
22M.2.hl.TZ1.2c(ii):
The reaction is first order with respect to HCl. Calculate the time taken, in seconds (s), for half of the Mg to dissolve when [HCl] = 0.5 mol dm^–3.
22M.1.hl.TZ1.20: The table shows data for the hydrolysis of a halogenoalkane, RCl. Which statements are...
22M.1.hl.TZ1.21:
What is the activation energy according to the following plot of the linear form of the Arrhenius equation?

Arrhenius equation: $k = A e^{\frac{- E a}{R T}}$ .

A. $E_{a} = \frac{2 \times 8.31}{0.06}$

B. $E_{a} = \frac{- 2 \times 8.31}{0.06}$

C. $E_{a} = e^{\frac{2 \times 8.31}{0.06}}$

D. $E_{a} = e^{\frac{- 2 \times 8.31}{0.06}}$
17M.1.hl.TZ2.21: Which is correct about reaction mechanisms? A. A species that is zero order does not...
18M.1.hl.TZ2.20: When X reacts with Y to give Z, the following graph is plotted. What can be deduced from the...
17M.2.hl.TZ1.1d:
When the reaction is carried out in the absence of acid the following graph is obtained.

Discuss the shape of the graph between A and B.
22M.1.hl.TZ2.20: Which energy profile diagram represents an exothermic SN1 reaction?
17M.1.hl.TZ2.12: Which is the first step in the CFC-catalysed destruction of ozone in UV light? A. CCl2F2...
16N.2.hl.TZ0.3e:
(i) Using the graph, explain the order of reaction with respect to sodium thiosulfate.

(ii) In a different experiment, this reaction was found to be first order with respect to hydrochloric acid. Deduce the overall rate expression for the reaction.
18M.1.hl.TZ1.19: What are correct labels for the Maxwell−Boltzmann energy distribution curves?
18M.1.hl.TZ1.20: The reaction between NO2 and F2 gives the following rate data at a certain...
18M.1.hl.TZ2.21: Which statement is correct? A. The value of the rate constant, k, is independent of...
18M.2.hl.TZ1.4b.iv:
Deduce the rate expression for the reaction.
22M.2.hl.TZ2.4a(ii):
Deduce the rate expression for the reaction.
22M.2.hl.TZ2.4a(i):
Deduce the order of reaction with respect to hydrogen.
22M.2.hl.TZ2.4a(iii):
Calculate the value of the rate constant stating its units.
17M.2.hl.TZ2.5b.v:
Sketch the relationship between the rate of reaction and the concentration of NO₂.
18M.2.hl.TZ1.4b.v:
Calculate the rate constant of the reaction, stating its units.
18N.1.hl.TZ0.20: Compounds X and Y were mixed and the time taken for a colour to appear was recorded at...
18N.1.hl.TZ0.21:
The rate expression for the reaction is: rate = k [NO]²[O₂].

2NO (g) + O₂ (g) → 2NO₂ (g)

Which mechanism is not consistent with this rate expression?
18N.2.hl.TZ0.10a: Classify substances B and D as reactant, product, catalyst, or intermediate, based on the...
18N.2.hl.TZ0.10b:
Deduce the rate expression.
18N.2.hl.TZ0.10c: Calculate the initial rate of reaction for experiment 2, if measured under the same...
17M.1.hl.TZ1.20:
The table gives rate data for the reaction in a suitable solvent.

C₄H₉Br + OH⁻ → C₄H₉OH + Br⁻

Which statement is correct?

A. The rate expression is rate = k [C₄H₉Br] [OH⁻].

B. The rate increases by a factor of 4 when the [OH⁻] is doubled.

C. C₄H₉Br is a primary halogenoalkane.

D. The reaction occurs via S_N1 mechanism.
17M.2.hl.TZ1.1c:
When the concentration of iodine is varied, while keeping the concentrations of acid and propanone constant, the following graphs are obtained.

Deduce, giving your reason, the order of reaction with respect to iodine.
16N.1.hl.TZ0.22:
Decomposition of hydrogen peroxide in an aqueous solution proceeds as follows.

2H₂O₂(aq) → 2H₂O(l) + O₂(g)

The rate expression for the reaction was found to be: rate = k [H₂O₂].

Which graph is consistent with the given rate expression?
19M.1.hl.TZ1.20: Which graph is obtained from a first order reaction?
19M.1.hl.TZ1.21: Which is correct for the reaction mechanism shown?
19M.1.hl.TZ2.20:
Which statement is correct about a catalyst?

A. It decreases the activation energy of the forward reaction but not the reverse.

B. It increases the proportion of products to reactants in an equilibrium.

C. It decreases the enthalpy change of the reaction.

D. It changes the mechanism of the reaction.
19M.2.hl.TZ2.2c(i):
Deduce how the rate of reaction at t = 2 would compare to the initial rate.
17N.1.hl.TZ0.21:
The rate expression for the reaction X (g) + 2Y (g) → 3Z (g) is

rate = k[X]⁰ [Y]²

By which factor will the rate of reaction increase when the concentrations of X and Y are both increased by a factor of 3?

A. 6

B. 9

C. 18

D. 27
17M.2.hl.TZ2.5b.iii:
State one method that can be used to measure the rate for this reaction.
16N.1.hl.TZ0.21: Which statement describes the characteristics of a transition state relative to the potential...
17N.1.hl.TZ0.22: Which pair of statements explains the increase in rate of reaction when the temperature...
17N.2.hl.TZ0.2e.ii:
State the rate expression for the reaction.
21N.1.hl.TZ0.20: Which graph shows a first order reaction?
17N.2.hl.TZ0.2e.i: Deduce the order of reaction with respect to Cl2 and NO.
19M.2.hl.TZ1.4b(ii):
Two more trials (2 and 3) were carried out. The results are given below.

Determine the rate equation for the reaction and its overall order, using your answer from (b)(i).

Rate equation:

Overall order:
19N.2.hl.TZ0.1e(i): Identify the steps which absorb ultraviolet light.
19N.2.hl.TZ0.3b(i):
Determine the rate expression from the results, explaining your method.
21M.1.hl.TZ1.20:
A reaction proceeds by the following mechanism:

step 1: $A + A \to B$
step 2: $B + C \to D$

Which rate equation is consistent with this mechanism?

A. Rate = k[B]²[C]

B. Rate = k[A]²[B][C]

C. Rate = k[A]²

D. Rate = k[A][C]
17M.2.hl.TZ1.1b:
The student then carried out the experiment at other acid concentrations with all other conditions remaining unchanged.

Determine the relationship between the rate of reaction and the concentration of acid and the order of reaction with respect to hydrogen ions.
17M.2.hl.TZ2.5b.i:
State the rate expression for the reaction.
19N.1.hl.TZ0.21: Which is correct?
19M.1.hl.TZ2.21:
What is the order with respect to each reactant?

2NO (g) + Cl₂ (g) → 2NOCl (g)
19M.2.hl.TZ2.2c(ii):
It has been suggested that the reaction occurs as a two-step process:

Step 1: N₂O (g) → N₂ (g) + O (g)

Step 2: N₂O (g) + O (g) → N₂ (g) + O₂ (g)

Explain how this could support the observed rate expression.
21M.1.hl.TZ1.21: Which graphs show a first order reaction? A. V and X B. V and Y C. W and X D. W and Y
17M.2.hl.TZ2.5b.ii:
The following mechanism is proposed for the reaction.

$\begin{array}{*{20}{l}} {{\text{Step I}}}&{{\text{N}}{{\text{O}}_{\text{2}}}{\text{(g)}} + {\text{N}}{{\text{O}}_{\text{2}}}{\text{(g)}} \to {\text{NO(g)}} + {\text{N}}{{\text{O}}_{\text{3}}}{\text{(g)}}} \\ {{\text{Step II}}}&{{\text{N}}{{\text{O}}_{\text{3}}}{\text{(g)}} + {\text{CO(g)}} \to {\text{N}}{{\text{O}}_{\text{2}}}{\text{(g)}} + {\text{C}}{{\text{O}}_{\text{2}}}{\text{(g)}}} \end{array}$

Identify the rate determining step giving your reason.
21N.2.hl.TZ0.10c(ii): Deduce the units of the rate constant.
21N.2.hl.TZ0.10d: Deduce, with a reason, the mechanism of the reaction between 2-chloropentane and sodium...
21M.2.hl.TZ1.6b(iii):
Write the rate expression for this reaction.
21M.2.hl.TZ1.6b(iv):
Calculate the value of the rate constant, k, giving its units.
21M.1.hl.TZ2.20: Which graph represents a second order reaction with respect to X? X → Y
21M.2.hl.TZ2.6a:
Determine the rate expression for the reaction.
21M.2.hl.TZ2.6b:
Determine the value and unit of the rate constant using the rate expression in (a).
20N.1.hl.TZ0.21:
Which graph represents the relationship between the rate constant, $k$ , and temperature, $T$ , in kelvin?
17M.1.hl.TZ1.21:
What are the units for the rate constant, k, in the expression?

Rate = k [X]²[Y]

A. mol² dm⁻⁶ s⁻¹

B. mol⁻¹ dm³ s⁻¹

C. mol dm⁻³ s⁻¹

D. mol⁻² dm⁶ s⁻¹
21N.2.hl.TZ0.10c(i):
Deduce the rate expression for this reaction.
21M.2.hl.TZ1.7c:
Explain, using equations, how the presence of ${CCl}_{2} F_{2}$ results in a chain reaction that decreases the concentration of ozone in the stratosphere.
21N.1.hl.TZ0.21:
The rate equation for a reaction is:

rate = k[A][B]

Which mechanism is consistent with this rate equation?

A. 2A $⇌$ I Fast
I + B → P Slow

B. A + B $⇌$ I Fast
I + A → P Slow

C. A → I Slow
I + B → P Fast

D. B $⇌$ I Fast
I + A → P Slow
21N.2.hl.TZ0.10c(iii):
Determine the initial rate of reaction in experiment 4.

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Additional higher level (AHL) » Topic 16: Chemical kinetics

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