DP Chemistry Questionbank

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?

(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.

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

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

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

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

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

Which graph represents the relationship between the rate constant, $k$, and temperature, $T$, in kelvin?

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.

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

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.

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.

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.

Which is true of an Arrhenius plot of $\ln k$ (y-axis) against $\frac{1}{T}$?

A.     The graph goes through the origin.

B.     The activation energy can be determined from the gradient.

C.     The intercept on the x-axis is the activation energy.

D.     The intercept on the y-axis is the frequency factor, A.

State the rate expression for the reaction.

The following mechanism is proposed for the reaction.

Identify the rate determining step giving your reason.

State one method that can be used to measure the rate for this reaction.

Sketch the relationship between the rate of reaction and the concentration of NO₂.

The Arrhenius equation, $k=A{e}^{-\frac{Ea}{RT}}$, gives the relationship between the rate constant and temperature.

State how temperature affects activation energy.

State the rate expression for the reaction.

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

A reaction proceeds by the following mechanism:

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

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]

Calculate the value of the rate constant, k, giving its units.

Write the rate expression for this reaction.

Explain, using equations, how the presence of ${\text{CCl}}_{\text{2}}{\text{F}}_{\text{2}}$ results in a chain reaction that decreases the concentration of ozone in the stratosphere.

Determine the rate expression for the reaction.

Determine the value and unit of the rate constant using the rate expression in (a).

Deduce the rate expression for the reaction.

Calculate the rate constant of the reaction, stating its units.

Describe how the activation energy of this reaction could be determined.

The rate constant for a reaction doubles when the temperature is increased from 25.0 °C to 35 °C.

Calculate the activation energy, E_a, in kJ mol⁻¹ for the reaction using section 1 and 2 of the data booklet.

The rate equation for a reaction is:

rate = k[A][B]

Which mechanism is consistent with this rate equation?

A.  2A $\rightleftharpoons$ I       Fast
     I + B → P    Slow

B.  A + B $\rightleftharpoons$ I   Fast
     I + A → P    Slow

C.  A → I          Slow
     I + B → P    Fast

D.  B $\rightleftharpoons$ I         Fast
     I + A → P    Slow

Deduce the rate expression for this reaction.

Determine the initial rate of reaction in experiment 4.

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?

Deduce the rate expression.

What is the activation energy according to the following plot of the linear form of the Arrhenius equation?

Arrhenius equation: $k=A{e}^{\frac{\mathit{-}Ea}{RT}}$.

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.  $E_a=e^{\frac{-2\times 8.31}{0.06}}$

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.

Use the graph to deduce the dependence of the reaction rate on the amount of Mg.

Deduce the rate expression for the reaction.

Calculate the value of the rate constant stating its units.

Deduce the order of reaction with respect to hydrogen.

Deduce how the rate of reaction at t = 2 would compare to the initial rate.

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.

What is the order with respect to each reactant?

2NO (g) + Cl₂ (g) → 2NOCl (g)

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.

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: 

What is the intercept on the y-axis when a graph of lnk is plotted against $\frac{1}{T}$ on the x-axis?

$\ln k=-\frac{E_a}{RT}+\ln A$

A.  lnA

B.  $-\frac{E_{\mathrm{a}}}{R}$

C.  $-\frac{R}{E_{\mathrm{a}}}$

D.   $E_{\mathrm{a}}$

Determine the rate expression from the results, explaining your method.