May/June 2018

This question concerns isolated gaseous atoms. Which atom has every electron paired?

Atomic structure

Element X has a greater first ionisation energy than element Y. Two students each give what they think is a reason for this. student 1: "X has a greater first ionisation energy than Y because an atom of X contains more protons in its nucleus than an atom of Y." student 2: "X has a greater first ionisation energy than Y because X has a smaller atomic radius than Y." Only one of these students is right. What could X and Y be?

The Periodic Table: chemical periodicity

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

Reaction kinetics

Silicon is heated with chlorine in excess, forming compound J. Excess water is then added to the J sample that is formed. Which row is correct?

Chemical bonding

Which element has the second-smallest atomic radius within its group and the third-lowest first ionisation energy across its period?

The Periodic Table: chemical periodicity

When chlorine reacts with cold aqueous sodium hydroxide, sodium chloride, water and compound X are formed. When chlorine reacts with hot aqueous sodium hydroxide, sodium chloride, water and compound Y are formed. What are the oxidation states of chlorine in compound X and compound Y?

Electrochemistry

In which reaction does ammonia act as a Brønsted-Lowry base?

Equilibria

A solution of potassium iodide is treated with aqueous silver nitrate. Next, aqueous ammonia is added. What observations would be made?

Group 17

Oxides of nitrogen occur in the environment because of both natural and human-made sources. Which row is correct?

Nitrogen and sulfur

When $3.00\,\text{g}$ of a Group 2 metal anhydrous nitrate is decomposed, $1.53\,\text{g}$ of gas is produced. What is the nitrate compound?

Atoms, molecules and stoichiometry

Which row gives the correct description of one property of barium and one property of barium oxide?

Group 2

Which compound’s boiling point is affected by hydrogen bonding?

States of matter

Fructose is a sugar that has more than one chiral centre. In the diagram of the fructose molecule, X, Y and Z label three carbon atoms. Which of these carbon atoms are chiral centres?

Chemical bonding

Which two alcohols are isomers of one another?

Hydroxy compounds

Sodium methoxide, $\text{Na}^+\text{CH}_3\text{O}^-$, undergoes nucleophilic substitution with 2-chloro-2-methylpropane. The nucleophile is the $\text{CH}_3\text{O}^-$ ion. Which row is correct?

Halogen compounds

Which alcohol can be dehydrated to produce two products that are structural isomers of one another?

Hydroxy compounds

Which reagent could be used to detect alcohol in a mixture made up mainly of alkanes and alkenes?

Hydroxy compounds

Compound Q • has a chiral centre, • produces a positive result with Fehling’s reagent, • produces a positive result with alkaline aqueous iodine. What might compound Q be?

Carbonyl compounds

What mechanism explains the reaction between ethanal, $\text{CH}_3\text{CHO}$, and hydrogen cyanide, $\text{HCN}$, when $\text{NaCN}$ is present?

Carbonyl compounds

Ethyl propanoate is heated under reflux with aqueous sodium hydroxide. The alcohol formed is then reacted with methyl propanoic acid to produce a second ester. What is the structural formula for this second ester?

Carboxylic acids and derivatives

What reagent could be used to perform the reaction shown below?

Organic synthesis

Four reactions of propanoic acid that produce salts and other products are shown. Which reaction does not display the formulae for all of the correct products?

Carboxylic acids and derivatives

Which fuel would generate the greatest mass of $\text{CO}_2$ when $10\,\text{kg}$ of the fuel is completely combusted?

Atoms, molecules and stoichiometry

Compound X has three carbon atoms. A section of the simplified infra-red spectrum for compound X is displayed. Which compound might X be?

Chemical bonding

Aqueous solution is prepared using one mole of sulfuric acid. It contains $\text{H}_2\text{SO}_4$ molecules, $\text{H}^+$ ions, $\text{SO}_4^{2-}$ ions and $\text{HSO}_4^-$ ions. Which of these statements are correct?

Equilibria

Which of the following statements are correct?

Atoms, molecules and stoichiometry

When calcium reacts with water, calcium hydroxide and hydrogen are produced. $\text{Ca(s)} + 2\text{H}_2\text{O(l)} \rightarrow \text{Ca(OH)}_2\text{(s)} + \text{H}_2\text{(g)}$ For this reaction, the standard enthalpy change is $-414\,\text{kJ mol}^{-1}$. What additional information is required to determine the standard enthalpy change of formation of calcium hydroxide, $\Delta H_f^\circ(\text{Ca(OH)}_2\text{(s)})$?

Chemical energetics

Which statements are correct when a reversible reaction has reached equilibrium?

Equilibria

A chemical reaction can occur for each of the three mixtures shown. Which of these mixtures gives a redox reaction?

Electrochemistry

Which statements accurately describe how a nitrogen oxide acts as an atmospheric pollutant?

Nitrogen and sulfur

The chain fragment of polymer Z is shown below. This particular section occurs many times in the chains of polymer Z, but it is not the repeat unit. $-\text{CH}_2-\text{CHCl}-\text{CH}_2-$ What might polymer Z be called?

Chemical bonding

Limonene is present in lemons. Limonene is heated with concentrated acidified potassium manganate(VII). Which compounds are formed?

Hydrocarbons

Chlorofluoroalkanes have been used as refrigerants in refrigerators, but old refrigerators must be disposed of with care. Which statements about chlorofluoroalkanes are correct?

Chemical bonding

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?

Reaction kinetics

The $M_r$ value for compound X is $72$. By mass, X contains $66.7\%$ carbon, $11.1\%$ hydrogen and $22.2\%$ oxygen. X produces an orange precipitate with 2,4-dinitrophenylhydrazine reagent. X shows no reaction with Fehling’s reagent. From this information, what can be inferred?

Carbonyl compounds

Which molecule has no net dipole?

Chemical bonding

Which solid has more than one kind of bonding?

Chemical bonding

Enthalpy changes of combustion may be used to find enthalpy changes of formation. The equation below shows the enthalpy change of formation of butane. $4\text{C}(s) + 5\text{H}_2(g) \rightarrow \text{C}_4\text{H}_{10}(g)$ Using the standard enthalpy of combustion data given below, what is the value of the standard enthalpy change of formation, $\Delta H_f^{\circ}$, of butane?

Chemical energetics

When ethanedioate ions, $\text{C}_2\text{O}_4^{2-}$, react with an appropriate reagent, $\text{CO}_2$ is produced. The half-equation for this reaction is given below. $\text{C}_2\text{O}_4^{2-} \rightarrow 2\text{CO}_2 + 2e^-$ Which row is the correct one?

Electrochemistry

Use oxidation numbers to answer this question. A redox reaction occurs between hydroxylammonium ions, $[\text{NH}_3\text{OH}]^+$, and acidified iron(III) ions, $\text{Fe}^{3+}$. The products are iron(II) ions, $\text{Fe}^{2+}$, $\text{H}^+$ ions, water, and a nitrogen compound. The mole ratio of hydroxylammonium ions reacting to iron(III) ions reacting is $1:2$. Which nitrogen-containing compound could be produced in the reaction?

Electrochemistry

What characteristic is shared by both ethene and poly(ethene)?

Chemical bonding

For a certain reversible reaction, the product yield rises • when the temperature is raised; • when the pressure is lowered. Which equation might represent this reversible reaction?

Equilibria

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?

Reaction kinetics

Which oxide fails to react with cold, dilute sodium hydroxide to form a salt?

The Periodic Table: chemical periodicity

The graphs illustrate patterns in four physical properties of the elements in Period 3, with argon left out. Which graph shows electronegativity on the $y$-axis?

The Periodic Table: chemical periodicity

In this question, X denotes an atom of chlorine, bromine or iodine. Which explanation of the change in volatility down Group 17 is correct?

States of matter

In cement manufacture, 1000 million tonnes of limestone are decomposed each year. For producing lime used in agriculture, 200 million tonnes of limestone are decomposed each year. What is the combined mass of carbon dioxide, in million tonnes, generated in a year by these two processes?

Atoms, molecules and stoichiometry

In Group 2 of the Periodic Table, the properties of the elements and their compounds change regularly down the group. Which property decreases from magnesium to barium?

Group 2

When concentrated sulfuric acid is added to solid sodium bromide, bromine gas is formed together with several other products. However, when concentrated sulfuric acid is added to solid sodium chloride, only hydrogen chloride and sodium hydrogensulfate are formed. What accounts for this difference?

Group 17

The dative covalent bond may be shown with an arrow, $\rightarrow$. The arrow is drawn towards the atom that accepts the lone pair. Which diagram of an ammonium ion is correct?

Chemical bonding

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

Reaction kinetics

The electronic configuration of a sulfur atom is $1s^2 2s^2 2p^6 3s^2 3p^4$. In one sulfur atom, how many electrons are in the valence shell, and how many electrons are unpaired?

Atomic structure

Compound Y is reacted with an excess of hydrogen gas in the presence of a nickel catalyst. The product becomes fully saturated. What is the number of chiral carbon atoms in the product?

Chemical bonding

Which equation shows a correct propagation step in the chlorination of ethane?

Hydrocarbons

Maleic acid has applications in the food industry and also in drug stabilisation. It is the cis-isomer of butenedioic acid, and its structural formula is $\text{HO}_2\text{CCH}=\text{CHCO}_2\text{H}$. What product is produced when maleic acid reacts with cold, dilute, acidified manganate(VII) ions?

Hydrocarbons

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?

Reaction kinetics

When working through this question, take into account structural isomerism and stereoisomerism. A colourless liquid, $\text{C}_5\text{H}_{11}\text{Cl}$, occurs as a mixture of two optical isomers. If it is heated with sodium hydroxide in ethanol, just a mixture of two alkenes is produced. What might the colourless liquid be?

Halogen compounds

If warm water is introduced to halogenoalkane X, an $S_N1$ reaction takes place. $\text{AgNO}_3(aq)$ is then added, and a yellow precipitate appears. What could X be?

Halogen compounds

Which alcohol reacts with acidified potassium dichromate(VI) solution to form a ketone with six carbon atoms?

Hydroxy compounds

Which statement concerning butanone is correct?

Carbonyl compounds

Ethanal, $\text{CH}_3\text{CHO}$, is used in the preparation of product R by means of a three-stage synthesis. $\text{CH}_3\text{CHO} \xrightarrow[\text{NaCN}]{\text{HCN}} \text{product P} \xrightarrow[\text{reflux}]{\text{H}_2\text{SO}_4\text{(aq)}} \text{product Q} \xrightarrow[\text{a few drops}]{\text{conc. }\text{H}_2\text{SO}_4} \text{product R}$ In the reaction, two molecules of Q combine to form one molecule of R and two molecules of water. Each molecule of R contains two ester functional groups. Sodium does not react with R. Determine the empirical formula of R.

Carboxylic acids and derivatives

The ester ethyl butanoate may be hydrolysed with excess dilute sodium hydroxide solution. Which substance is formed in this reaction?

Carboxylic acids and derivatives

In which pair does the second substance have a boiling point lower than the first substance?

States of matter

An infra-red spectrum of an organic compound is shown. Which compound might produce this spectrum?

Chemical bonding

In complete combustion, $1\,$mol of an organic compound X needs $2.5\,$mol of $\text{O}_2$. Which compounds might X be?

Atoms, molecules and stoichiometry

Which pairs contain species with the same number of electrons?

Atomic structure

For which reactions does the value of $\Delta H^\circ$ correspond to both a standard enthalpy change of combustion and a standard enthalpy change of formation?

Chemical energetics

The temperature of a reversible reaction in the gas phase is raised. Which of the following statements are always correct?

Equilibria

Each of three chlorine gas samples contains $0.710\,$g of chlorine. A reagent is used to react with each sample. • In the first reaction, one sample is reacted fully with hydrogen gas. • In the second reaction, one sample is reacted fully with cold $\text{NaOH(aq)}$. • In the third reaction, one sample is reacted fully with hot $\text{NaOH(aq)}$. Which masses of the named products would be produced?

Atoms, molecules and stoichiometry

Solid barium oxide is added to a sample of ammonium sulfate solution in a test tube, and the mixture is heated. A piece of damp red litmus paper is then held above the mouth of the test tube. What observations would be seen?

Nitrogen and sulfur

Among the following compounds, which can exhibit geometrical (cis-trans) isomerism?

Chemical bonding

Which pairs of compounds can be told apart by carrying out a test with alkaline aqueous iodine?

Analytical techniques

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

Reaction kinetics

Compound J reacts with excess oxygen to produce only carbon dioxide and water. If a $3.00\,\text{g}$ sample of compound J is burned in excess oxygen, $4.40\,\text{g}$ of carbon dioxide and $1.80\,\text{g}$ of water are produced. What is the empirical formula of J?

Atoms, molecules and stoichiometry

The ester $\text{C}_2\text{H}_5\text{CO}_2\text{CH}_2\text{CH}_2\text{CH}_3$ may be prepared in a school or college laboratory by using compound Z as the only organic starting material in a route of four reactions or fewer. What could the identity of compound Z be?

Organic synthesis

The gases X and Y react to make Z. $\text{X}(g) + \text{Y}(g) \rightleftharpoons \text{Z}(g)$ This equilibrium mixture of the three gases is then compressed at constant temperature. What changes will occur in the mole fraction of Z and in $K_p$?

Equilibria

Which gas is most likely to show the greatest departure from ideal gas behaviour?

States of matter

For reaction 1, the enthalpy change is $-114\,\text{kJ mol}^{-1}$. $2\text{NaOH}(aq) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{Na}_2\text{SO}_4(aq) + 2\text{H}_2\text{O}(l)$ (reaction 1) Using this data, what is the best estimate for the enthalpy change of reaction 2? $\text{Ba(OH)}_2(aq) + 2\text{HCl}(aq) \rightarrow \text{BaCl}_2(aq) + 2\text{H}_2\text{O}(l)$ (reaction 2)

Chemical energetics

Sulfur undergoes a redox reaction with concentrated nitric acid. $\text{S} + 4\text{HNO}_3 \rightarrow \text{SO}_2 + 4\text{NO}_2 + 2\text{H}_2\text{O}$ State the changes in oxidation number for sulfur and for nitrogen in this reaction.

Electrochemistry

Materials may be classified according to their chemical structures. Four standard types of structure are metallic, ionic, simple molecular and giant molecular. The table lists some physical properties of four substances. Which of the substances has a simple molecular structure?

Chemical bonding

What explains why ammonia, $\text{NH}_3$, has a higher boiling point than phosphine, $\text{PH}_3$?

States of matter

This equilibrium is established when ammonia is made by the Haber process. $\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3$ At equilibrium, the concentrations present under specific conditions are as follows. $[\text{N}_2] = 0.200\ \text{mol dm}^{-3}$, $[\text{H}_2] = 0.300\ \text{mol dm}^{-3}$, $[\text{NH}_3] = 0.600\ \text{mol dm}^{-3}$ What numerical value does $K_c$ have under these conditions?

Equilibria

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?

Reaction kinetics

Which statement correctly describes the bonding and acid/base properties of aluminium oxide?

Chemical bonding

X and Y are elements from the third period. X and Y are each heated separately in excess chlorine. Their products are purified and then added one by one to water, forming two solutions. The pH of both solutions is less than 5. Which substances could X and Y be?

Chemical bonding

An ore includes magnesium carbonate and barium carbonate. A portion of the ore is dissolved in nitric acid. How can this solution be treated to obtain a magnesium compound and a separate barium compound?

Group 2

When calcium and calcium hydride, $\text{CaH}_2$, react independently with water, each reaction forms a white solid and a colourless gas. In both cases, the white solid is the same compound. Which of the following statements is correct?

Group 2

When concentrated sulfuric acid is added to solid sodium chloride, HCl is produced but not $\text{Cl}_2$. When concentrated sulfuric acid is added to solid sodium iodide, $\text{I}_2$ is produced. Which statement accounts for these observations?

Electrochemistry

When silver chloride and silver iodide are added to water, equilibria are set up. $\text{AgCl}(s) \rightleftharpoons \text{Ag}^+(aq) + \text{Cl}^-(aq) \quad K_c = K_1$ $\text{AgI}(s) \rightleftharpoons \text{Ag}^+(aq) + \text{I}^-(aq) \quad K_c = K_2$ The equilibrium position for each of these lies far to the left. Silver iodide does not dissolve in aqueous ammonia, but silver chloride does dissolve in aqueous ammonia. A further equilibrium is established. $\text{Ag}^+(aq) + 2\text{NH}_3(aq) \rightleftharpoons \text{Ag(NH}_3\text{)}_2^+(aq) \quad K_c = K_3$ This equilibrium position lies to the right. What order of magnitude do these three equilibrium constants have?

Equilibria

Elements and their compounds play an important role as catalysts. In which process is a compound used instead of an element?

Reaction kinetics

The gaseous substances produced when a mixture of $\text{Ca(OH)}_2$ and $\text{NH}_4\text{Cl}$ is heated are led over solid CaO. The CaO removes water vapour, and gas W is then collected. A sample of W is oxidised by $\text{Cl}_2(g)$, forming two gases, X and Y. X is an element. Y is acidic. Y reacts with W to form Z. Identify X and Z.

Nitrogen and sulfur

A beam of neutrons is sent through an electric field. The mass of a single neutron, compared with $\frac{1}{12}$ of the mass of a $^{12}\text{C}$ atom, and any deflection produced by the electric field are recorded. Which row is correct?

Atomic structure

The structure of molecule G is displayed. How many chiral centres are there in each molecule of G?

Chemical bonding

Sibirene, $\text{C}_{15}\text{H}_{24}$, is allowed to react with an excess of $\text{HBr}(g)$. The main product formed is X. What is the skeletal formula for X?

Hydrocarbons

Which statement is incorrect?

Atoms, molecules and stoichiometry

The presence of a halogen in an organic compound may be identified by heating the organic compound with aqueous silver nitrate. Which compound would form a precipitate most rapidly?

Reaction kinetics

Halogenoalkanes undergo reaction with $\text{NaOH(aq)}$ by either an $S_N1$ mechanism or an $S_N2$ mechanism. The mechanism used in the reaction is determined by the structure of the halogenoalkane. In this question, the reaction of 3-bromo-3-ethylpentane, $(\text{C}_2\text{H}_5)_3\text{CBr}$, is considered. Which statement is the correct one?

Reaction kinetics

Which compound is a secondary alcohol and, on dehydration, produces an alkene with $M_r = 70$?

Hydroxy compounds

If $0.0075\,\text{mol}$ of alcohol $X$ is fully combusted in an excess of oxygen, and the resulting gases are then bubbled through excess limewater (calcium hydroxide solution), $3.0\,\text{g}$ of calcium carbonate are formed. When $X$ is heated with acidified potassium dichromate(VI), the colour changes from orange to green. What might the identity of $X$ be?

Atoms, molecules and stoichiometry

If only structural isomers are included, how many alcohols of each kind have the formula $\text{C}_5\text{H}_{12}\text{O}$?

Chemical bonding

A student performed a two-stage synthesis where $\text{CH}_3\text{CH}_2\text{CH}_2\text{Br}$ was changed into $\text{CH}_3\text{CH}_2\text{CH}_2\text{CO}_2\text{H}$. Which compound may have been produced in the first stage of this synthesis?

Atoms, molecules and stoichiometry

An ester $X$ has the structural formula $\text{CH}_3\text{CO}_2\text{CH(CH}_3)\text{CH}_2\text{CH}_3$. $X$ may be made by heating an alcohol $Y$ under reflux with ethanoic acid and an acid catalyst. What is the correct name of $Y$?

Hydroxy compounds

The table shows the electron arrangement in the second shell of an atom that has eight protons. Which row is correct for this atom?

Atomic structure

Compound $S$ may be obtained from natural compounds. When $S$ is treated with hot, concentrated $\text{KMnO}_4$, the organic product $T$ is formed. Several absorptions in the infra-red spectra of $S$ and $T$ are given. $S$ shows no strong absorption between $1670$ and $1740\,\text{cm}^{-1}$. $T$ shows a strong absorption at $1720\,\text{cm}^{-1}$, but it does not show any strong, broad absorption between $2500$ and $3000\,\text{cm}^{-1}$. On the basis of this information, what might the formulae of $S$ and $T$ be?

Analytical techniques

A hydrocarbon sample was completely burned, producing $0.132\,\text{g}$ of carbon dioxide and $0.054\,\text{g}$ of water. Which formulae could be correct for this hydrocarbon?

Atoms, molecules and stoichiometry

Which of the following statements are correct?

Atoms, molecules and stoichiometry

Ammonia and chlorine react according to the equation shown. $8\text{NH}_3 + 3\text{Cl}_2 \rightarrow \text{N}_2 + 6\text{NH}_4\text{Cl}$. Which statements are true?

Atoms, molecules and stoichiometry

The diagram illustrates the reaction profile for a reversible reaction. Which of the following statements are correct? 1. The forward reaction is exothermic. 2. The enthalpy change for the forward reaction is $-30\ \text{kJ mol}^{-1}$. 3. The enthalpy change for the backward reaction is $+90\ \text{kJ mol}^{-1}$.

Chemical energetics

Metals are thought to consist of positive ions in a sea of delocalised electrons. For the metals in Period 3, melting points rise as atomic number rises. Which of these statements can be used to account for this pattern from sodium to aluminium? 1. The metal ion has a higher charge. 2. Each metal ion is associated with a greater number of delocalised electrons. 3. The radius of the metal ion decreases.

Chemical bonding

A sample of gas, $X$, occupies $600\ \text{cm}^3$ under room conditions and has a mass of $0.700\ \text{g}$. Which gas could $X$ be? 1. carbon monoxide gas 2. ethene gas 3. nitrogen gas

Atoms, molecules and stoichiometry

After treatment with $\text{NaBH}_4$, which of these compounds gives a product that contains a chiral carbon atom? 1. $\text{CH}_3\text{CH}_2\text{CH}_2\text{COCH}_3$ 2. $\text{CH}_2\text{CHCOCH}_2\text{CH}_3$ 3. $\text{CH}_3\text{CH}_2\text{COCH}_2\text{CH}_3$

Carbonyl compounds

Compound $Y$ is an unbranched molecule with formula $\text{C}_n\text{H}_{2n+1}X$. $X$ is a halogen. The $M_r$ of $Y$ is $137$. The halogen atom is bonded to the second carbon atom in the chain. Which statements are correct? 1. $Y$ has a chiral centre. 2. $Y$ can eliminate $HX$ to produce two structurally isomeric alkenes. 3. $Y$ can eliminate $HX$ to produce two geometrically isomeric alkenes.

Chemical bonding

Propanone and hydrogen cyanide react by the mechanism illustrated. Which of the following statements about this mechanism are correct? 1. $\text{CN}^-$ acts as an electrophile. 2. The reaction is an addition reaction. 3. Heterolytic bond breaking occurs.

Carbonyl compounds

Which statement describes the bond joining carbon and hydrogen in an ethene molecule?

Chemical bonding

Acrolein is an organic compound whose molecular formula is $\text{C}_3\text{H}_4\text{O}$. It has uses in water treatment and as a herbicide. When acrolein is reacted with $2,4$-dinitrophenylhydrazine, an orange precipitate forms. Acrolein gives a silver mirror with Tollens’ reagent. Which of the following statements are correct? 1. Acrolein reacts with alkaline aqueous iodine to form a yellow precipitate. 2. Acrolein can be reduced to a primary alcohol. 3. Acrolein decolourises bromine water.

Carbonyl compounds

Aspirin, $\text{C}_9\text{H}_8\text{O}_4$, $M_r = 180.0$, may be prepared by reacting 2-hydroxybenzoic acid, $\text{C}_7\text{H}_6\text{O}_3$, $M_r = 138.0$, with ethanoic anhydride, $\text{C}_4\text{H}_6\text{O}_3$, $M_r = 102.0$. The balanced equation for this reaction is shown. $\text{C}_7\text{H}_6\text{O}_3 + \text{C}_4\text{H}_6\text{O}_3 \rightarrow \text{C}_9\text{H}_8\text{O}_4 + \text{C}_2\text{H}_4\text{O}_2$ If the reaction mixture contains $10.0\,\text{g}$ of each reactant, what is the greatest mass of aspirin that can be formed?

Atoms, molecules and stoichiometry

Which diagram accurately shows the behaviour of a fixed mass of an ideal gas? ($T$ is measured in $\text{K}$.)

States of matter

When anhydrous copper(II) chloride, $\text{CuCl}_2$, reacts with water, $\text{CuCl}_2\cdot2\text{H}_2\text{O}$ is formed. The standard enthalpy changes of formation for this reaction are listed in the table. What is the standard enthalpy change for the reaction shown? $\text{CuCl}_2 + 2\text{H}_2\text{O} \rightarrow \text{CuCl}_2\cdot2\text{H}_2\text{O}$

Chemical energetics

When xenon hexafluoride, $\text{XeF}_6$, is added to water, it reacts. $\text{XeF}_6 + 3\text{H}_2\text{O} \rightarrow \text{XeO}_3 + 6\text{HF}$ Which of the following statements is correct?

The Periodic Table: chemical periodicity

The industrial manufacture of hydrogen from methane is represented by the equation below. $\text{CH}_4(\text{g}) + \text{H}_2\text{O}(\text{g}) \rightleftharpoons \text{CO}(\text{g}) + 3\text{H}_2(\text{g}) \quad \Delta H^{\circ} = +205\,\text{kJ mol}^{-1}$ Under what conditions would hydrogen formation be favoured most?

Equilibria