Reaction kinetics

A chemist places a sample of dilute aqueous hydrochloric acid into beaker 1. She adds zinc and measures the rate at which hydrogen gas is produced. She then places a different sample of dilute aqueous hydrochloric acid into beaker 2. She adds a different sample of zinc and measures the rate at which hydrogen gas is produced. The reaction in beaker 2 happens faster than the reaction in beaker 1. Which factors could account for this observation?

Feb/March 2016

Chlorine atoms in the upper atmosphere lead to ozone being broken down. $\text{Cl} + \text{O}_3 \rightarrow \text{O}_2 + \text{ClO}$ $\text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2$ Which statements are correct when these chlorine atoms are being considered?

Feb/March 2016

The oxidation of ethanedioate ions by acidified manganate(VII) ions proceeds very slowly at room temperature. $2\text{MnO}_4^- + 5\text{C}_2\text{O}_4^{2-} + 16\text{H}^+ \rightarrow 2\text{Mn}^{2+} + 10\text{CO}_2 + 8\text{H}_2\text{O}$ $\text{Mn}^{2+}$ ions act as catalysts for this reaction. Which graph shows the way the concentration of acidified manganate(VII) ions changes after ethanedioate ions are added?

Feb/March 2017

Which statement correctly describes the effect of a catalyst on a reversible reaction?

Feb/March 2018

A Boltzmann distribution is given for a gas sample at an initial temperature, $T_1$. The gas sample is then heated to temperature, $T_2$. Which distribution correctly represents the gas at the higher temperature, $T_2$?

Feb/March 2019

A catalytic converter is used to take away some polluting gases from car exhaust fumes. Platinum or palladium may be used as the catalyst. The reactions proceed more quickly with platinum than they do with palladium. Which statements are correct?

Feb/March 2019

Chlorine atoms present in the upper atmosphere bring about the breakdown of ozone. $\text{Cl} + \text{O}_3 \rightarrow \text{O}_2 + \text{ClO}$ $\text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2$ Which of the following statements about these chlorine atoms are correct?

Feb/March 2019

Zinc reacts with hydrochloric acid. $\text{2HCl (aq)} + \text{Zn (s)} \rightarrow \text{ZnCl}_2 \text{ (aq)} + \text{H}_2 \text{ (g)}$ Which change would make this reaction faster but leave the Boltzmann distribution of molecular energies unchanged?

Feb/March 2020

Ethanal and hydrogen cyanide react with each other. Cyanide ions take part in the reaction mechanism. Which statements about this mechanism are correct?

Feb/March 2020

The Boltzmann distribution curve for a gaseous mixture of ethene and hydrogen is shown. Nickel is an effective catalyst for the reaction that occurs. How would the diagram be different if the same reaction mixture were at a higher temperature?

Feb/March 2021

Hydrogen peroxide, $\text{H}_2\text{O}_2$, breaks down to produce water and oxygen. Bromide ions catalyse the reaction. first step $2\text{Br}^-(aq) + \text{H}_2\text{O}_2(aq) + 2\text{H}^+(aq) \rightarrow 2\text{H}_2\text{O}(l) + \text{Br}_2(aq)$ second step $\text{H}_2\text{O}_2(aq) + \text{Br}_2(aq) \rightarrow 2\text{Br}^-(aq) + 2\text{H}^+(aq) + \text{O}_2(g)$ Which row is the correct one?

Feb/March 2022

A Boltzmann distribution for one mole of a gas at temperature $T$ is displayed. A further one mole of the same gas is then introduced, while the gas stays at temperature $T$. Which dotted line represents the distribution after the extra gas has been added?

Feb/March 2022

For the reaction shown, the concentrations of both X and Y are each lowered to one half of their starting values while the total volume of the solution remains unchanged. $\text{X(aq)} + \text{Y(aq)} \rightarrow \text{XY(aq)}$ At the same time, the temperature is raised from $298\,\text{K}$ to $348\,\text{K}$. Which prediction is certainly correct?

Feb/March 2022

Alkenes undergo reaction with aqueous hydrogen bromide. This reaction takes place through a carbocation intermediate. The more stable the intermediate is, the more quickly the reaction occurs. Which sequence correctly indicates an increase in the rate of reaction of the alkenes with hydrogen bromide?

Feb/March 2022

The diagram illustrates the structures of three halogenoalkanes P, Q and R. All three, P, Q and R, are capable of hydrolysis. Which row is correct?

Feb/March 2022

The diagram illustrates the Boltzmann distribution for one mole of a gas. This gas reacts in a reaction with activation energy, $E_a$. Which statement correctly explains the effect of an increase in temperature?

Feb/March 2023

A student performs four tests to study the rate of reaction between $3.0\,\text{g}$ of calcium carbonate and hydrochloric acid. $\text{CaCO}_3(s) + 2\text{HCl}(aq) \rightarrow \text{CaCl}_2(aq) + \text{CO}_2(g) + \text{H}_2\text{O}(l)$ test 1: $\text{CaCO}_3$ powder + $2.0\,\text{mol dm}^{-3}\,\text{HCl}$ at $35\,^\circ\text{C}$ test 2: $\text{CaCO}_3$ powder + $2.0\,\text{mol dm}^{-3}\,\text{HCl}$ at $35\,^\circ\text{C}$ test 3: large chips of $\text{CaCO}_3$ + $1.0\,\text{mol dm}^{-3}\,\text{HCl}$ at room temperature test 4: large chips of $\text{CaCO}_3$ + $1.0\,\text{mol dm}^{-3}\,\text{HCl}$ at $35\,^\circ\text{C}$ The student gathers the $\text{CO}_2(g)$ and measures the time needed to obtain the same gas volume in each test. Which set of times could be correct for the four tests?

Feb/March 2023

Exhaust gases from an internal combustion engine are made less harmful when they are passed through a catalytic converter. Several reactions occur in the catalytic converter. Two of these reactions are shown in the table. Which row is the correct one?

Feb/March 2023

Two experiments are performed to investigate the reaction between zinc and sulfuric acid. experiment 1: Small pieces of zinc are placed into an excess of dilute sulfuric acid. experiment 2: The reaction is carried out at a lower temperature, together with one further alteration. Both experiments give the same total volume of gas and finish in the same time. What is the other change made in experiment 2?

Feb/March 2024

The diagram illustrates the procedure of placing calcium nitrate and strontium nitrate into separate boiling tubes and then heating them. The same conditions are applied. While the reactions continue, the water containing universal indicator changes colour. Which row gives the colour change and identifies the nitrate that produces the fastest colour change?

Feb/March 2024

A Boltzmann distribution for a sample of reacting gas at constant temperature is shown. The activation energy, $E_A$, for the reaction is indicated. Point \times indicates the number of particles whose energy equals the activation energy. The temperature of the gas sample is reduced. The form of the distribution curve changes. Which point could represent the number of particles whose energy is equal to the activation energy at the lower temperature?

Feb/March 2025

An aqueous solution of hydrogen peroxide is added to a flask and breaks down, as shown. $\text{2H}_2\text{O}_2(aq) \rightarrow \text{2H}_2\text{O}(l) + \text{O}_2(g)$ The total volume of oxygen gas released is $180\,\text{cm}^3$ after $90$ seconds, measured at room conditions. The rate of the reaction is found using the equation shown. $\text{rate} = \frac{\text{change in moles of } \text{H}_2\text{O}_2}{\text{time}}$ What is the mean rate of the reaction, in $\text{mol min}^{-1}$, during the experiment?

Feb/March 2025

$\text{Na}_2\text{S}_2\text{O}_3$ reacts with dilute $\text{HCl}$, producing a pale yellow precipitate. When $1\,\text{cm}^3$ of $0.1\,\text{mol dm}^{-3}$ $\text{HCl}$ is mixed with $10\,\text{cm}^3$ of $0.02\,\text{mol dm}^{-3}$ $\text{Na}_2\text{S}_2\text{O}_3$, the precipitate appears slowly. When the experiment is repeated using $1\,\text{cm}^3$ of $0.1\,\text{mol dm}^{-3}$ $\text{HCl}$ and $10\,\text{cm}^3$ of $0.05\,\text{mol dm}^{-3}$ $\text{Na}_2\text{S}_2\text{O}_3$, the precipitate appears more quickly. What is the reason for this?

May/June 2010

When 2,2-dimethylbutane is heated with chlorine, it undergoes free radical substitution. In one propagation step, the free radical $X\cdot$ is produced. $\text{CH}_3\text{CH}_2\!\!\begin{matrix} \\ | \end{matrix}C\!\!\begin{matrix} \\ | \end{matrix}\text{CH}_3 + \text{Cl}\cdot \rightarrow X\cdot + \text{HCl}$ How many different forms of $X\cdot$ can be formed?

May/June 2010

For an isomer $Y$ with molecular formula $\text{C}_4\text{H}_9\text{Br}$, hydrolysis in aqueous alkali produces the alcohol $\text{C}_4\text{H}_9\text{OH}$. The reaction rate is observed to remain unchanged when the concentration of $\text{OH}^-$ ions present is varied. Which molecular structure is most likely to be $Y$?

May/June 2010

$\text{Na}_2\text{S}_2\text{O}_3$ reacts with dilute $\text{HCl}$ and produces a pale yellow precipitate. When $1\ \text{cm}^3$ of $0.1\ \text{mol dm}^{-3}\ \text{HCl}$ is added to $10\ \text{cm}^3$ of $0.02\ \text{mol dm}^{-3}\ \text{Na}_2\text{S}_2\text{O}_3$, the precipitate appears slowly. If the test is done again using $1\ \text{cm}^3$ of $0.1\ \text{mol dm}^{-3}\ \text{HCl}$ and $10\ \text{cm}^3$ of $0.05\ \text{mol dm}^{-3}\ \text{Na}_2\text{S}_2\text{O}_3$, the precipitate appears more rapidly. What accounts for this?

May/June 2010

When an isomer Y with molecular formula $\text{C}_4\text{H}_9\text{Br}$ is hydrolysed in aqueous alkali to give an alcohol $\text{C}_4\text{H}_9\text{OH}$, the reaction rate is observed to remain unchanged when the concentration of $\text{OH}^-$ ions present is altered. Which molecular structure of Y is the most likely?

May/June 2010

$\text{Na}_2\text{S}_2\text{O}_3$ reacts with dilute $\text{HCl}$ to form a pale yellow precipitate. When $1\,\text{cm}^3$ of $0.1\,\text{mol dm}^{-3}$ $\text{HCl}$ is mixed with $10\,\text{cm}^3$ of $0.02\,\text{mol dm}^{-3}$ $\text{Na}_2\text{S}_2\text{O}_3$, the precipitate appears slowly. When the experiment is carried out again using $1\,\text{cm}^3$ of $0.1\,\text{mol dm}^{-3}$ $\text{HCl}$ and $10\,\text{cm}^3$ of $0.05\,\text{mol dm}^{-3}$ $\text{Na}_2\text{S}_2\text{O}_3$, the precipitate appears more rapidly. Why does this happen?

May/June 2010

On heating with chlorine, the hydrocarbon $2,2$-dimethylbutane undergoes free radical substitution. During a propagation stage, the free radical $X^\bullet$ is produced. $\text{CH}_3\text{CH}_2\!\!\begin{array}{c}\text{C}\\|\\\text{CH}_3\end{array}\!\!\text{CH}_3\; + \text{Cl}^\bullet \rightarrow X^\bullet + \text{HCl}$ How many different forms of $X^\bullet$ can be formed?

May/June 2010

When an isomer Y with molecular formula $\text{C}_4\text{H}_9\text{Br}$ is hydrolysed in aqueous alkali to give an alcohol $\text{C}_4\text{H}_9\text{OH}$, the reaction rate is observed to remain unchanged when the concentration of $\text{OH}^-$ ions present is altered. Which molecular structure is most likely to be Y?

May/June 2010

Hydrazine, $\text{N}_2\text{H}_4$, is commonly used as a rocket fuel because it reacts with oxygen in the way shown, giving ‘environmentally friendly’ gases. $\text{N}_2\text{H}_4\text{(l)} + \text{O}_2\text{(g)} \rightarrow \text{N}_2\text{(g)} + 2\text{H}_2\text{O(g)} \quad \Delta H = -534 \text{ kJ mol}^{-1}$. Even though hydrazine is used as a rocket fuel, it does not burn spontaneously in oxygen. Which statement gives the reason hydrazine does not burn spontaneously?

May/June 2011

The diagrams show different Boltzmann distributions. In diagram 1, one of the curves, P or Q, represents the higher temperature than the other curve. In diagram 2, one of the lines, X or Y, shows the activation energy for a catalysed reaction, while the other line shows the activation energy for the same reaction when it is uncatalysed. Which combination identifies the correct curve and line?

May/June 2011

In the diagram, curve X was produced by monitoring the decomposition of $100\,\text{cm}^3$ of $1.0\,\text{mol dm}^{-3}$ hydrogen peroxide, with manganese(IV) oxide acting as the catalyst. Which change to the starting experimental conditions would result in curve Y?

May/June 2011

A solid sample of calcium carbonate is placed into $100\ \text{cm}^3$ of dilute hydrochloric acid, and the reaction rate is measured. A second $100\ \text{cm}^3$ portion of the acid is then mixed with $100\ \text{cm}^3$ of distilled water, and the experiment is repeated under identical conditions. Why does adding water lower the rate of the reaction?

May/June 2011

The Boltzmann distribution for a gas at constant temperature is illustrated below. If the gas temperature is lowered by $10\,^{\circ}\text{C}$, the shape of the graph alters. What happens to the values of $n$ at the points labelled $X$, $Y$ and $Z$?

May/June 2011

Hydrazine, $\text{N}_2\text{H}_4$, is used extensively as a rocket fuel because it reacts with oxygen in the way shown, forming ‘environmentally friendly’ gases. $\text{N}_2\text{H}_4(l) + \text{O}_2(g) \rightarrow \text{N}_2(g) + 2\text{H}_2\text{O}(g) \quad \Delta H = -534\,\text{kJ mol}^{-1}$ Even though hydrazine is employed as a rocket fuel, it does not ignite of its own accord in oxygen. Which statement accounts for why hydrazine does not burn spontaneously?

May/June 2011

In the diagram, curve X was produced by monitoring the decomposition of $100\ \text{cm}^3$ of $1.0\ \text{mol dm}^{-3}$ hydrogen peroxide, catalysed by manganese(IV) oxide. Which change to the original experimental conditions would produce curve Y?

May/June 2011

The diagrams show two Boltzmann distributions. For diagram 1, one of the curves P or Q represents a temperature that is greater than the temperature of the other curve. For diagram 2, one of the lines X or Y represents the activation energy for a catalysed reaction, and the other line represents the activation energy for the same reaction when uncatalysed. Which combination gives the correct curve and line?

May/June 2011

Ammonia is produced by the Haber Process in an exothermic reaction. If the amount of catalyst is kept constant, which change would not cause an increase in the rate of the forward reaction?

May/June 2012

The molecular energy distribution curve shows how the energy of the molecules in a gas varies at room temperature. Which curve is correct for the same gas at a lower temperature?

May/June 2012

Oct-1-ene, $\text{CH}_3(\text{CH}_2)_5\text{CH}=\text{CH}_2$, undergoes thermal cracking. Which set of compounds W, X, Y and Z could be formed? $\text{W}: \text{CH}_2=\text{CH}_2$ $\text{X}: \text{CH}_3\text{CH}=\text{CH}_2$ $\text{Y}: \text{CH}_3\text{CH}_2\text{CH}_3$ $\text{Z}: \text{CH}_2=\text{CHCH}=\text{CH}_2$

May/June 2012

Which statements concerning the photochemical chlorination of ethane are correct?

May/June 2012

Ammonia is produced by the Haber Process in an exothermic reaction. If the amount of catalyst is kept constant, which change will not cause the rate of the forward reaction to increase?

May/June 2012

A halogen in an organic compound can be detected by heating the organic compound with aqueous silver nitrate. Which compound would form a precipitate most rapidly?

May/June 2012

An experiment is arranged to determine the rate of hydrolysis of ethyl ethanoate. $\text{CH}_3\text{CO}_2\text{C}_2\text{H}_5 + \text{H}_2\text{O} \rightleftharpoons \text{CH}_3\text{CO}_2\text{H} + \text{C}_2\text{H}_5\text{OH}$ It is observed that the hydrolysis is slow in neutral aqueous solution, but it takes place at a measurable rate when the solution is acidified with hydrochloric acid. What does the hydrochloric acid do?

May/June 2013

What causes the rate of a gaseous reaction to rise when the pressure is increased at a constant temperature?

May/June 2013

On heating with chlorine, the hydrocarbon $2,2$-dimethylbutane undergoes free radical substitution. During a propagation step, a free radical $X\bullet$ is produced: $\text{CH}_3\text{CH}_2\text{C(CH}_3)_2\text{CH}_3 + \text{Cl}\bullet \rightarrow X\bullet + \text{HCl}$. How many different forms of $X\bullet$ can exist?

May/June 2013

When 2-bromo-2-methylpropane is treated with aqueous sodium hydroxide, 2-methylpropan-2-ol is formed. The reaction follows an $S_N1$ mechanism. How should the initial step in the mechanism be described?

May/June 2013

Sulfur dioxide is an atmospheric pollutant responsible for acid rain. One reaction in this sequence is the conversion of sulfur dioxide into sulfur trioxide by oxidation. This oxidation occurs in a two-stage reaction that involves oxygen and nitrogen monoxide, NO. $\text{NO} + \frac{1}{2}\text{O}_2 \rightarrow \text{NO}_2$ $\text{NO}_2 + \text{SO}_2 \rightarrow \text{SO}_3 + \text{NO}$ Which of the following statements are correct?

May/June 2013

What factor can influence the value of the activation energy of a reaction?

May/June 2013

Transition elements and their compounds are important as catalysts. In which process is a compound of a transition element used instead of the element itself?

May/June 2013

When methane is brominated, the free radical $\text{CH}_3\boldsymbol{\cdot}$ is formed. One possible termination stage for this reaction is the production of $\text{C}_2\text{H}_6$ when two free radicals combine. What could be produced in a terminating step during the bromination of propane?

May/June 2013

The diagram shows, at a specified temperature, the Boltzmann distribution of the kinetic energies of the molecules in a mixture of two gases that react with each other. The activation energy for the reaction, $E_a$, is indicated. The dotted curves below illustrate the Boltzmann distribution for the same reaction at a higher temperature. In these diagrams, H denotes the activation energy at the higher temperature. Which diagram is correct?

May/June 2013

Crotonaldehyde, $\text{CH}_3\text{CH}={CHCHO}$, may be prepared by oxidising butadiene, $\text{CH}_2=\text{CHCH}=\text{CH}_2$, with air or oxygen. In one process, a blend of butadiene and oxygen is passed through a hot aqueous solution of palladium(II) ions, $\text{Pd}^{2+}(aq)$, which act as the catalyst for the reaction. Which statement is not correct about the role of the $\text{Pd}^{2+}(aq)$ ions?

May/June 2013

Boltzmann distributions are displayed in the diagrams. For diagram 1, either curve P or Q represents the higher temperature than the other curve. For diagram 2, either line X or Y represents the activation energy when a catalyst is present, while the other line shows the activation energy for the same reaction when no catalyst is present. Which combination gives the correct curve and line?

May/June 2014

A number of organic reactions have to be warmed before they take place, although others do not need heating. Which reaction takes place rapidly at room temperature?

May/June 2014

The hydrolysis of 1-chloropropane to form propan-1-ol occurs much more slowly than the equivalent hydrolysis of 1-iodopropane. Which statement accounts for this observation?

May/June 2014

R and S combine in a reversible reaction, $\text{R} + \text{S} \rightleftharpoons \text{T}$. Which factors influence the speed of the forward reaction?

May/June 2014

During the manufacture of sparkler fireworks, a paste made from barium nitrate powder, aluminium powder, water and glue is spread onto wires and left to dry. At this point, the following exothermic reaction may take place. $16\text{Al} + 3\text{Ba(NO}_3)_2 + 36\text{H}_2\text{O} \rightarrow 3\text{Ba(OH)}_2 + 16\text{Al(OH)}_3 + 6\text{NH}_3$ Which conditions would be most suitable for slowing the rate of this reaction while the aluminium and barium nitrate remain unchanged?

May/June 2014

The diagram illustrates a Boltzmann distribution for the molecular energies in a gaseous mixture. The distribution has a maximum, marked $P$ on the diagram. What occurs when the temperature of the mixture rises?

May/June 2014

Platinum catalyses the reaction $E + F \rightleftharpoons G + H$. Which of these statements about the catalyst’s properties are correct?

May/June 2014

On the diagram, curve $X$ was produced by monitoring the decomposition of $100\,\text{cm}^3$ of $1.0\,\text{mol dm}^{-3}$ hydrogen peroxide, with manganese(IV) oxide as the catalyst. Which change to the original experimental conditions would give curve $Y$?

May/June 2014

The Boltzmann distribution for a gas at a constant temperature is shown below. If the gas temperature is lowered by $10^{\circ}\text{C}$, the graph alters its form. What happens to the values of $n$ for the molecular energies $X$, $Y$ and $Z$?

May/June 2014

The stoichiometry for a catalysed reaction is represented by the equation below. $\text{P}(g) + \text{Q}(g) \rightleftharpoons \text{R}(g) + \text{S}(l)$ In two experiments, the rate at which $\text{R}$ was formed was measured. The outcomes are given in the diagram below. Which changes in the conditions might explain the results shown?

May/June 2014

The diagram depicts an experimental arrangement that can be used in several different experiments. Which processes could be shown using the apparatus above?

May/June 2014

Hydrazine, $\text{N}_2\text{H}_4$, is employed as a rocket fuel since it reacts with oxygen according to the equation shown, giving gases that are considered environmentally friendly. $\text{N}_2\text{H}_4(\ell) + \text{O}_2(\text{g}) \rightarrow \text{N}_2(\text{g}) + 2\text{H}_2\text{O}(\text{g}) \quad \Delta H = -534\,\text{kJ mol}^{-1}$. Although hydrazine is used as a rocket fuel, it does not ignite spontaneously in oxygen. Which statement accounts for the fact that hydrazine does not burn spontaneously?

May/June 2014

The diagram illustrates a Boltzmann distribution for the molecular energies in a gaseous mixture. A peak on the diagram is labelled P. What happens when an effective catalyst is added to the mixture?

May/June 2015

The diagram illustrates the reaction pathway for an endothermic reaction. Which arrow shows the activation energy for the forward reaction?

May/June 2015

Which intermediate ion is produced in the greatest quantity during the addition of HBr to propene?

May/June 2015

The presence of a halogen in an organic compound can be tested by heating the organic compound with aqueous silver nitrate. Which compound would form a precipitate in the shortest time?

May/June 2015

Why does increasing the pressure of a fixed mass of gaseous reactants at constant temperature make the rate of reaction rise?

May/June 2015

Propanone and hydrogen cyanide react with one another through this mechanism. Which statements about this mechanism are correct?

May/June 2015

The diagram illustrates the Boltzmann energy distribution curve for molecules in a mixture of two gases at a fixed temperature. For a reaction to take place, the molecules must collide with enough energy. $E_a$ is used to denote the activation energy for the reaction between the gases. From the two values shown, one is the activation energy for a catalysed reaction and the other is for an uncatalysed reaction. Which statement about $E_{a1}$ is correct?

May/June 2015

The Finkelstein reaction takes place when NaI in propanone reacts with a chloroalkane or bromoalkane. The halogen is substituted directly by I, and this reaction works only with primary halogenoalkanes. Which halogenoalkane would form compound X?

May/June 2015

A tertiary bromoalkane, shown here by $>\!\text{C-Br}$, is reacted with aqueous NaOH. The reaction route is given in the mechanism diagram below. Which point in the diagram is labelled correctly?

May/June 2015

Separate samples of 1-chlorobutane, 1-bromobutane and 1-iodobutane, four drops of each, were added to three different test-tubes that each contained $1.0\,\text{cm}^3$ of aqueous silver nitrate at $60\,^{\circ}\text{C}$. For all three halogenoalkanes, hydrolysis took place. R stands for the butane chain $\text{C}_4\text{H}_9$ and X stands for the halogen atom. $\text{H}_2\text{O}(l) + \text{R-X}(l) + \text{Ag}^+(aq) \rightarrow \text{R-OH}(aq) + \text{AgX}(s) + \text{H}^+(aq)$ The sequence for how quickly cloudiness appeared in the test-tubes was $\text{RCl} < \text{RBr} < \text{RI}$. Why is this?

May/June 2015

The reaction below was performed. $\text{HCO}_2\text{CH}_3(aq) + \text{NaOH}(aq) \rightarrow \text{HCO}_2\text{Na}(aq) + \text{CH}_3\text{OH}(aq)$ The concentration of methanol, $[\text{CH}_3\text{OH}(aq)]$, was recorded as time, $t$, passed. Which graph represents the link between $[\text{CH}_3\text{OH}(aq)]$ and $t$?

May/June 2015

Enzymes function as biological catalysts. A large number of enzymes are specific. One example of an enzyme that is specific is glucokinase. Glucokinase plays a part in the metabolism of glucose. What does specificity mean in this context?

May/June 2016

A student makes pentan-1-ol by carrying out the alkaline hydrolysis of 1-iodopentane. She warms the reaction mixture very gently for 20 minutes. $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{I} + \text{OH}^- \rightarrow \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{OH} + \text{I}^-$ If the student uses 1-chloropentane to prepare the same alcohol, she must alter the reaction conditions. Which change in condition should she make, and what is the correct reason for this change?

May/June 2016

The equation represents a reaction in the gas phase. $\text{X(g)} \rightarrow \text{2Y(g)}$ The diagram presents the Boltzmann distribution for a fixed mass of $\text{X(g)}$ at temperature $T$ when no catalyst is present. The line $E_A$ shows the activation energy. Which diagrams correctly illustrate the effect of each of the following changes made separately and independently?

May/June 2016

The diagram illustrates the Boltzmann distribution of energies for 1 mole of a gas. The gas may participate in a reaction with an activation energy, $E_a$. Which statement best describes the effect of a rise in temperature?

May/June 2016

Which stage in the free-radical substitution of ethane with chlorine has the lowest activation energy?

May/June 2016

Propanal reacts with hydrogen cyanide to give 2-hydroxybutanenitrile. One suitable catalyst for this reaction is sodium cyanide. $\text{CH}_3\text{CH}_2\text{CHO} + \text{HCN} \xrightarrow{\text{NaCN}} \text{CH}_3\text{CH}_2\text{CH(OH)CN}$ Which of the following statements about the reaction of propanal with hydrogen cyanide are correct?

May/June 2016

Catalysts are an important part of many industrial processes and biochemical reactions. Which row gives the correct description of the effect of a catalyst on a reversible chemical reaction?

May/June 2016

The diagram illustrates the Boltzmann distribution for the molecular energies in one mole of a gas at two temperatures, $T_1$ and $T_2$. Which of the statements are correct?

May/June 2016

Ethanal and hydrogen cyanide react together to produce a compound that is used in making acrylic fibres. The reaction mechanism involves cyanide ions. Which of the following statements about this mechanism are correct?

May/June 2016

Which changes may be used to measure the rates of chemical reactions?

May/June 2017

The Boltzmann distribution for the hydrogenation of an alkene at a specific temperature without a catalyst is shown. Which row correctly describes what happens when nickel is added to the reaction vessel?

May/June 2017

$\text{H}_2\text{NNHC}_6\text{H}_3(\text{NO}_2)_2$ gives the structural formula of 2,4-DNPH. A large number of organic reactions, though not all, have to be heated before they take place. Which reaction proceeds at a satisfactory rate at room temperature ($20\,^{\circ}\text{C}$)?

May/June 2017

The rate of a chemical reaction can be increased by adding a suitable catalyst. Which of these reactions can make use of a heterogeneous catalyst? 1 $\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3$ 2 $2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3$ 3 $2\text{NO} + 2\text{CO} \rightleftharpoons \text{N}_2 + 2\text{CO}_2$

May/June 2017

At the elevated temperatures found in car engines, nitrogen reacts with oxygen to produce nitrogen monoxide. $\tfrac{1}{2}\text{N}_2(g) + \tfrac{1}{2}\text{O}_2(g) \rightarrow \text{NO}(g) \quad \Delta H^\circ = +90\,\text{kJ mol}^{-1}$ This reaction has activation energy $E_a$. Which reaction pathway diagram could show this reaction correctly?

May/June 2017

The diagram illustrates the Boltzmann distribution for the energy of gaseous molecules at a given temperature. Which statement is correct?

May/June 2017

A student performed two experiments in which $\text{MnO}_2$ acted as a catalyst to break down hydrogen peroxide. The equation for this reaction is shown. $2\text{H}_2\text{O}_2\text{(aq)} \rightarrow 2\text{H}_2\text{O(l)} + \text{O}_2\text{(g)}$. Which statements are correct?

May/June 2017

Hydrogen ions act as catalysts for the hydrolysis of esters. Which of the following statements is correct?

May/June 2018

The diagram illustrates the Boltzmann distribution of energies for a gas. This gas is able to participate in a reaction with an activation energy, $E_a$. The gas is kept at a fixed temperature. Which statement is right?

May/June 2018

A chemical company employed a catalyst in a chemical process. It has now chosen not to use the catalyst, but instead to raise the temperature so that the rate of the reaction stays the same as it was when the catalyst was used. Which statement about the new conditions compared with the original conditions is correct?

May/June 2018

Sulfur dioxide can be catalytically oxidised in the atmosphere by an oxide of nitrogen. Which reaction shows the catalyst being regenerated?

May/June 2018

Primary halogenoalkanes take part in hydrolysis reactions. Which one of these reactions would happen at the greatest rate if each mixture were heated to the same temperature?

May/June 2018

The diagram illustrates an experimental set-up that may be used for several different experiments. Which processes can be shown using the apparatus above?

May/June 2018

The enzyme maltase catalyses the reaction between maltose and water. $\text{maltose} + \text{water} \xrightarrow{\text{maltase}} \text{glucose}$ Maltase is specific. Which statement explains the specificity of maltase?

May/June 2018