Feb/March 2025

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?

Reaction kinetics

Methanol is produced by the reaction of carbon dioxide with hydrogen. $\text{CO}_2(g) + 3\text{H}_2(g) \rightleftharpoons \text{CH}_3\text{OH}(g) + \text{H}_2\text{O}(g) \qquad \Delta H = -49\,\text{kJ mol}^{-1}$ What change increases the equilibrium yield of methanol for this process?

Equilibria

The equation for a reaction involving $\text{KClO}_3$ is given below. $4\text{KClO}_3 \rightarrow \text{KCl} + 3\text{KClO}_4$ Which row is correct?

Group 17

A student combines $25.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ sodium hydroxide solution with $25.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ hydrochloric acid, and the student measures a temperature increase of $2.50\,^{\circ}\text{C}$. What is the enthalpy change of the reaction per mole of NaOH?

Chemical energetics

Carbon monoxide and methanol may react together to produce ethanoic acid. $\text{CO}(g) + \text{CH}_3\text{OH}(l) \xrightarrow[]{\Delta H^{\circ}} \text{CH}_3\text{CO}_2\text{H}(l)$ The table lists the standard enthalpy changes of combustion. $\Delta H_c^{\circ}(\text{CO}) = -283.0\,\text{kJ mol}^{-1}$ $\Delta H_c^{\circ}(\text{CH}_3\text{OH}) = -726.0\,\text{kJ mol}^{-1}$ $\Delta H_c^{\circ}(\text{CH}_3\text{CO}_2\text{H}) = -874.1\,\text{kJ mol}^{-1}$ Determine the value of $\Delta H_r^{\circ}$ for the reaction between carbon monoxide and methanol?

Chemical energetics

Copper undergoes reaction with nitric acid in certain conditions. The products formed are copper(II) nitrate, water and a nitrogen oxide. $3$ mol of copper reacts with exactly $8$ mol of nitric acid. What is the oxidation state of nitrogen in the oxide formed?

Electrochemistry

Every reactant and product in an exothermic reaction is in the gaseous state. Which statement about this reaction is correct?

Chemical energetics

Propene, hydrogen cyanide and carbon dioxide all have $\pi$ bonds. Which of these molecules has two $\pi$ bonds?

Chemical bonding

Q, R and S are adjacent elements in Period $3$ of the Periodic Table. Element R has the greatest first ionisation energy and the smallest melting point among these three elements. What are the identities of Q, R and S?

The Periodic Table: chemical periodicity

A reaction sequence for a Group $2$ metal, M, is shown. $\text{M} \xrightarrow[]{\text{reacts with oxygen}} \text{X} \xrightarrow[]{\text{reacts with water}} \text{Y} \xrightarrow[]{\text{reacts with sulfuric acid}} \text{Z}$ Which row is right as M moves down Group $2$ from Mg to Ba?

Group 2

U, V and W are three different halogens. The table summarises nine experiments in which aqueous $\text{U}_2$, $\text{V}_2$ and $\text{W}_2$ were each added separately to aqueous solutions containing $\text{U}^-$, $\text{V}^-$ and $\text{W}^-$ ions. (Results summary) $\text{U}_2(aq)$ does not react with $\text{U}^-(aq)$, $\text{V}^-(aq)$ or $\text{W}^-(aq)$. $\text{V}_2(aq)$ produces $\text{U}_2$ with $\text{U}^-(aq)$, does not react with $\text{V}^-(aq)$, and produces $\text{W}_2$ with $\text{W}^-(aq)$. $\text{W}_2(aq)$ produces $\text{U}_2$ with $\text{U}^-(aq)$ and does not react with $\text{V}^-(aq)$ or $\text{W}^-(aq)$. Which row gives the ions $\text{U}^-$, $\text{V}^-$ and $\text{W}^-$ in descending order of reducing strength?

Electrochemistry

Copper(II) nitrate crystals are made by reacting nitric acid with an excess of malachite. Malachite has the formula $\text{Cu(OH)}_2\cdot\text{CuCO}_3$, $(M_r = 221.0)$. A sample of $12.0\,\text{g}$ of malachite is added to $30.0\,\text{cm}^3$ of $1.50\,\text{mol dm}^{-3}$ nitric acid. What mass of malachite remains unreacted after the reaction has finished?

Atoms, molecules and stoichiometry

J can be $\text{MgCl}_2$ or $\text{AlCl}_3$. K can be $\text{SiO}_2$ or $\text{SiCl}_4$. $\text{J}(aq) \xrightarrow[]{\text{add drops of aqueous sodium hydroxide}}$ white precipitate $\xrightarrow[]{\text{add an excess of aqueous sodium hydroxide}}$ precipitate dissolves $\text{K} \xrightarrow[]{\text{add water}}$ misty white fumes and a white precipitate in a solution with $\text{pH} < 7$ Which row is the correct one?

The Periodic Table: chemical periodicity

River water from an agricultural area contains $\text{NH}_4^+$, $\text{CO}_3^{2-}$, $\text{HCO}_3^-$, $\text{Cl}^-$ and $\text{NO}_3^-$ ions. A calculated amount of calcium hydroxide is then added to treat this water. What precipitate is formed when calcium hydroxide is added to the river water?

Equilibria

Four atmospheric pollutants are given below. 1 nitrogen oxides 2 carbon monoxide 3 unburnt hydrocarbons 4 sulfur dioxide Which two pollutants react together to produce peroxyacetyl nitrate, PAN?

Nitrogen and sulfur

Which graph correctly shows a trend observed in Group 17? [X stands for a halogen atom.]

Group 17

Gas M is formed when $\text{NH}_4\text{Cl(aq)}$ is heated together with $\text{CaO(s)}$. Which row is correct?

Nitrogen and sulfur

The two nitrates undergo thermal decomposition on heating, as given by the equations below. $2\text{Pb(NO}_3)_2\text{(s)} \rightarrow 2\text{PbO(s)} + 4\text{NO}_2\text{(g)} + \text{O}_2\text{(g)}$ $2\text{NH}_4\text{NO}_3\text{(s)} \rightarrow 2\text{N}_2\text{(g)} + \text{O}_2\text{(g)} + 4\text{H}_2\text{O(l)}$ A separate sample of one mole of each nitrate is heated. The gas formed in each case is then passed through $\text{NaOH(aq)}$. After that, the volume of any gas that does not react with $\text{NaOH(aq)}$ is collected and measured. Which nitrate undergoes the larger percentage decrease in mass and gives the larger volume of gas collected?

Atoms, molecules and stoichiometry

Organic compound X has empirical formula $\text{C}_2\text{H}_4\text{O}$. Compound X is reduced by $\text{LiAlH}_4$, but it is not reduced by $\text{NaBH}_4$. What is compound X?

Atomic structure

What mechanism describes the reaction between hydrogen cyanide and propanone?

Carbonyl compounds

Which compound could be made from an alkene with formula $\text{C}_4\text{H}_8$ by an addition reaction?

Hydrocarbons

The structure of compound G is illustrated below. Compound G undergoes addition polymerisation. Which diagram represents the repeat unit of the polymer that is produced?

Chemical bonding

X and Y are elements in the same group of the Periodic Table. The 5th to 9th ionisation energies of X and Y are given. Ionisation energy / $\text{kJ mol}^{-1}$: Element X: 5th $11020$, 6th $15160$, 7th $17870$, 8th $92040$, 9th $106437$. Element Y: 5th $6540$, 6th $9360$, 7th $11020$, 8th $33360$, 9th $38600$. Which row is used to identify elements X and Y?

The Periodic Table: chemical periodicity

Compound T is examined with three reagents, and the observations are shown below. 2,4-DNPH: orange precipitate Fehling’s solution: no reaction acidified $\text{K}_2\text{Cr}_2\text{O}_7$: no reaction Identify compound T.

Chemical bonding

Reagent X is introduced separately to 2-methylbutan-1-ol and 3-methylbutan-2-ol. The observations seen are not the same. What is reagent X?

Hydroxy compounds

Compound Y is broken down by warm aqueous silver nitrate to give a precipitate that dissolves in dilute aqueous ammonia. Compound Y then undergoes an elimination reaction to produce an alkene. What is the skeletal formula for compound Y?

Halogen compounds

Propan-2-ol can be changed into 2-chloropropane by using reagent M first and then reagent N. Which row is correct?

Halogen compounds

The skeletal formulae for four organic compounds are displayed. Which two compounds, when each is heated separately with dilute sulfuric acid, produce propanoic acid as one of the products?

Carboxylic acids and derivatives

1-chloro-2-methylpropane and 2-bromo-2-methylbutane are each reacted separately with aqueous silver nitrate in ethanol. In both cases, nucleophilic substitution occurs and a precipitate is produced. The time needed for 1-chloro-2-methylpropane to produce a precipitate is $T_1$. The time needed for 2-bromo-2-methylbutane to produce a precipitate is $T_2$. Which row is correct?

Halogen compounds

The diagram illustrates the structure of progesterone. Which of the following statements about progesterone is correct?

Carbonyl compounds

Hexane molecules can be cracked in several different ways. Three compounds are shown. 1 $\text{C}_3\text{H}_8$ 2 $\text{C}_4\text{H}_8$ 3 $\text{C}_5\text{H}_{12}$ Which of these compounds are present in the mixture of products obtained from cracking hexane molecules?

Atoms, molecules and stoichiometry

The diagrams illustrate the arrangements of two isomeric dicarboxylic acids, X and Y. X may be reduced to compound P, which has empirical formula $\text{C}_2\text{H}_5\text{O}$. Y may be reduced to compound Q, which also has empirical formula $\text{C}_2\text{H}_5\text{O}$. Which statement is correct?

Carboxylic acids and derivatives

What is the total number of $sp^3$ hybridised atomic orbitals involved in the bonding of but-2-ene?

Chemical bonding

An ion carrying a charge of $2-$ has $10$ electrons and $14$ neutrons. What is the nucleon number of this ion?

Atomic structure

Compound L is made up of carbon atoms. It is examined in a mass spectrometer. The table gives the relative abundance of the only two peaks detected with $m/e$ greater than 127. The peak at $m/e = 128$ has a relative abundance of 50. The peak at $m/e = 129$ has a relative abundance of 5.5. How many carbon atoms are present in one molecule of compound L?

Analytical techniques

The molecular structure of the hormone histamine is shown. Which row gives the bond angles $x$, $y$ and $z$ in histamine arranged correctly from the smallest to the largest?

An introduction to AS Level organic chemistry

When an organic acid is mixed with an alcohol, the reaction is reversible and produces an ester together with water. $0.40\,\text{mol}$ of an organic acid and $0.30\,\text{mol}$ of an alcohol are then combined and left at $25^\circ\text{C}$ until equilibrium is achieved. At equilibrium, $0.20\,\text{mol}$ of ester has formed. Calculate the equilibrium constant, $K_c$, for the conditions used?

Equilibria

Details of two substances are provided. Substance P: conducts electricity well in both the solid state and the molten state; when placed in water, it reacts vigorously to form an alkaline solution; melting point $454\,\text{K}$. Substance Q: does not conduct electricity in any state; when placed in water, it reacts vigorously to form an acidic solution; melting point $317\,\text{K}$. Which row gives the structure and bonding for substances P and Q?

Chemical bonding

An excess amount of zinc is reacted with $x\,\text{cm}^3$ of $2.00\,\text{mol dm}^{-3}$ hydrochloric acid. The gas formed is dried and then collected. At $101000\,\text{Pa}$ and $293\,\text{K}$, the gas has a volume of $1.534\,\text{dm}^3$. The gas formed follows ideal gas behaviour. Determine the value of $x$.

Atoms, molecules and stoichiometry

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?

Reaction kinetics

Phosphorus and chlorine are both elements in Period 3 of the Periodic Table.

Group 17

Define the term metallic bonding.

Group 2

The halogens chlorine, bromine and iodine display patterns in chemical and physical properties down the group. Table 3.1 gives some properties of chlorine, bromine and iodine.

Group 17

Fig. 4.1 presents compounds J to M, and each contains four carbon atoms.

Carbonyl compounds

Silver, Ag, is one of the metals in the d-block of the Periodic Table.

Chemical energetics

Propanone, $\text{CH}_3\text{COCH}_3$, is a familiar organic solvent and reagent. Under acidic conditions, propanone reacts with methanol, $\text{CH}_3\text{OH}$, to produce compound A, as shown in reaction 1: $\text{CH}_3\text{COCH}_3 + 2\text{CH}_3\text{OH} \xrightarrow{\text{H}^+} \text{A} + \text{H}_2\text{O}$ The overall order of reaction 1 can be determined from experimental observations. Table 2.1 shows the way the initial rate changes when $[\text{CH}_3\text{OH}]$ and $[\text{H}^+]$ are altered. In every experiment, a large excess of $\text{CH}_3\text{COCH}_3$ is employed.

Reaction kinetics

$\text{Fe}^{2+}$ and $\text{Fe}^{3+}$ ions can make a range of complexes with different species.

Chemistry of transition elements

State the relative basicities of ammonia, $\text{NH}_3$, propanamide, $\text{CH}_3\text{CH}_2\text{CONH}_2$, and propylamine, $\text{CH}_3\text{CH}_2\text{CH}_2\text{NH}_2$. Explain your answer.

States of matter

Cumene is an aromatic hydrocarbon that is used to make other useful chemicals.

Hydrocarbons

Maleic anhydride is an unsaturated cyclic compound that is used to make several polymers. It can be converted into maleic acid and tartaric acid, as shown in Fig. 6.1.

Chemistry of transition elements