May/June 2021

Which has the greatest number of hydrogen atoms?

Atoms, molecules and stoichiometry

The diagram shows the Haber process used to produce ammonia from nitrogen and hydrogen. What is the function of the heat exchanger?

Equilibria

Which statement concerning catalysts is correct?

Reaction kinetics

X is an element in Period 3. X makes a solid oxide, Y. Y undergoes reaction with hot concentrated hydrochloric acid. Y also reacts with hot aqueous sodium hydroxide, producing a compound in which X is present as part of an anion. How many $p$ electrons are there in the outer shell of one atom of X?

The Periodic Table: chemical periodicity

Heating a mixture of $\text{Ca(OH)}_2$ and $\text{NH}_4\text{Cl}$ gives gaseous products, which are then sent through solid $\text{CaO}$. One gaseous substance, W, is obtained. When a sample of W is allowed to react with $\text{Cl}_2(\text{g})$, two gases, X and Y, are formed. X is an element, whereas Y is acidic. Y reacts with W to form Z. Identify X and Z.

Nitrogen compounds

Q is made up of a Group 2 oxide and a Group 2 sulfate in equal quantities. When Q is shaken with water, the mixture is then filtered and a solid residue remains. The solid residue shows no reaction on shaking with $\text{HCl}(\text{aq})$. On shaking the filtrate with $\text{H}_2\text{SO}_4(\text{aq})$, a white precipitate is formed. What might Q be?

Group 2

Which substance is not formed during the thermal decomposition of hydrated magnesium nitrate?

Nitrogen and sulfur

A $5\,\text{cm}^3$ portion of $0.05\,\text{mol dm}^{-3}$ sodium chloride is combined with a $5\,\text{cm}^3$ portion of $0.05\,\text{mol dm}^{-3}$ potassium iodide. Next, $10\,\text{cm}^3$ of acidified $0.05\,\text{mol dm}^{-3}$ silver nitrate is added, and then concentrated ammonia solution is introduced. What observation is made after excess concentrated ammonia solution has been added?

Equilibria

The volatility of the Group 17 elements chlorine, bromine and iodine gets lower down the group. What causes this trend?

States of matter

Acid rain consists of a dilute solution of sulfuric acid. Which pollutant also helps in the formation of acid rain?

Nitrogen and sulfur

R is the oxide of the Period 3 element T. $5.00\,\text{g}$ of R contains $2.50\,\text{g}$ of T. Which element is T?

Atoms, molecules and stoichiometry

Which pair of species has both members with only one unpaired p electron?

Atomic structure

Cyanide ions react with bromoethane, giving propanenitrile. Which statement correctly describes the $\text{S}_\text{N}2$ mechanism for this reaction?

Halogen compounds

Which compound would form two different carboxylic acids on treatment with hot, concentrated, acidified manganate(VII) ions?

Hydrocarbons

Which compound might exhibit both cis-trans isomerism and optical isomerism?

An introduction to AS Level organic chemistry

Limonene is a hydrocarbon that occurs in the peel of citrus fruits. What is the molecular formula of limonene?

Atoms, molecules and stoichiometry

The compound cetyl palmitate, $\text{C}_{15}\text{H}_{31}\text{CO}_2\text{C}_{16}\text{H}_{33}$, is a wax-like solid. Cetyl palmitate is warmed under reflux with an excess of aqueous sodium hydroxide. Which products are formed?

Carboxylic acids and derivatives

If an organic compound undergoes oxidation, any oxygen atom incorporated into the organic molecule is taken to have come from a water molecule, which also forms $2\text{H}^+ + 2\text{e}^-$. Any hydrogen atom removed may be regarded as being lost as $\text{H}^+ + \text{e}^-.$ These alterations may be shown by the two equations below. $\text{H}_2\text{O} \rightarrow [\text{O}] + 2\text{H}^+ + 2\text{e}^-$ $[\text{H}] \rightarrow \text{H}^+ + \text{e}^-$ Compound X is oxidised by heating under reflux with hot, acidified potassium dichromate(VI) for one hour. The half-equation for the reduction reaction is shown. $\text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ + 6\text{e}^- \rightarrow 2\text{Cr}^{3+} + 7\text{H}_2\text{O}$ At these conditions, one mole of potassium dichromate(VI) oxidises three moles of X. What could X be?

Electrochemistry

Compound X has the empirical formula $\text{C}_2\text{H}_4\text{O}$. The infra-red spectrum for it is shown. What could the skeletal formula of compound X be?

Chemical bonding

What number of moles of hydrogen, $\text{H}_2$, is evolved when excess sodium metal is added to 1 mole of citric acid?

Atoms, molecules and stoichiometry

Which statement is correct about the reaction between carbonyl compounds and HCN?

Carbonyl compounds

The table shows four reactions involving propene. Which row is correct?

Hydrocarbons

Phosphorus can make two chlorides. Phosphorus(III) chloride, $\text{PCl}_3$, is a covalent liquid, whereas phosphorus(V) chloride is an ionic solid. One of the ions present is $[\text{PCl}_4]^+$. What is the shape of the $\text{PCl}_3$ molecule and the $[\text{PCl}_4]^+$ ion?

Chemical bonding

Butanoic acid is made starting from 1-bromopropane. The synthesis involves two reactions carried out in sequence. Which compound is produced in the first stage of the synthesis?

Organic synthesis

Ethanol reacts with ethanoic acid to produce ethyl ethanoate in the reaction shown below. $\text{C}_2\text{H}_5\text{OH}(l) + \text{CH}_3\text{CO}_2\text{H}(l) \rightleftharpoons \text{CH}_3\text{CO}_2\text{C}_2\text{H}_5(l) + \text{H}_2\text{O}(l)$ $\Delta H^\circ = -6\,\text{kJ mol}^{-1}$ 9.2 g of ethanol, 12 g of ethanoic acid and 8.8 g of ethyl ethanoate are combined and left at 298 K until equilibrium is attained. $(M_r:\ \text{C}_2\text{H}_5\text{OH},\ 46;\ \text{CH}_3\text{CO}_2\text{H},\ 60;\ \text{CH}_3\text{CO}_2\text{C}_2\text{H}_5,\ 88)$ The analysed equilibrium mixture is shown to have 4.8 g of ethanoic acid. The experiment is then carried out again at 323 K. Which statements are true?

Equilibria

The diagram below shows an unfinished energy profile diagram for a reaction. Which reactions could this diagram be describing? 1 $\text{CaCO}_3(s) \rightarrow \text{CaO}(s) + \text{CO}_2(g)$ 2 $\text{H}_2(g) \rightarrow 2\text{H}(g)$ 3 $\text{Cl}^-(aq) \rightarrow \text{Cl}(g) + aq$

Chemical energetics

A hydrocarbon in the gaseous state has a density of $2.42\,\text{g dm}^{-3}$ at room conditions. What could the skeletal formula of this hydrocarbon be?

Atoms, molecules and stoichiometry

Which of the following molecules includes at least one bond angle of $120^\circ$? 1 $\text{C}_2\text{H}_4$ 2 $\text{PF}_5$ 3 $\text{NCl}_3$

Chemical bonding

Which of the following statements are correct as you move across Period $3$ from sodium to chlorine? 1 The nuclear charge increases, so the electrons are attracted more strongly towards it. 2 The radius of the most common ion for each element gets smaller. 3 Shielding due to inner electrons decreases, so the outer electrons are drawn nearer to the nucleus.

The Periodic Table: chemical periodicity

Which of the following statements are correct? 1 Magnesium carbonate breaks down at a lower temperature than calcium carbonate. 2 Calcium hydroxide is more soluble in water than magnesium hydroxide. 3 Calcium is a stronger reducing agent than magnesium.

Group 2

Which of these statements are correct? 1 $1,1$-difluoroethane is less reactive than $1,1$-dichloroethane. 2 $1,1$-difluoroethane is polar. 3 The C-F bond is stronger than the C-Cl bond.

Chemical bonding

By using a test with alkaline aqueous iodine, which of the following pairs of compounds can be told apart? 1 butanal and butanone 2 pentan-$2$-one and pentan-$3$-ol 3 propanone and propan-$2$-ol

Carbonyl compounds

In which of these reactions is a coloured organic product formed? 1 ethanal + $2,4$-dinitrophenylhydrazine reagent 2 ethanol + acidified potassium dichromate(VI) 3 ethene + cold dilute acidified potassium manganate(VII)

Electrochemistry

$\Delta H_1^\circ$ represents the standard enthalpy of formation of methane. $\Delta H_2^\circ$ represents the standard enthalpy of combustion of carbon. $\Delta H_3^\circ$ represents the standard enthalpy of combustion of hydrogen. $\text{CH}_4(g) + 2\text{O}_2(g) \xrightarrow{\Delta H_c^\circ} \text{CO}_2(g) + 2\text{H}_2\text{O}(l)$ Which expression is equal to $\Delta H_c^\circ$?

Chemical energetics

Propanoic acid is made to react with an excess of lithium aluminium hydride. The organic compound obtained from this reaction is then reacted with ethanoic acid, with concentrated sulfuric acid present, to produce product X. What are the main commercial applications of X? 1 for fuel 2 as a solvent 3 for flavouring

Carboxylic acids and derivatives

The diagram illustrates the Boltzmann distribution for the same gas at two different temperatures, $T_1$ and $T_2$. What quantity is shown on the y-axis, and which curve corresponds to the higher temperature?

Reaction kinetics

What least mass of oxygen is required to make $12\,\text{dm}^3$ of propane burn completely at room conditions?

Atoms, molecules and stoichiometry

Why is the first ionisation energy of oxygen lower than that of nitrogen?

The Periodic Table: chemical periodicity

At room conditions, which gas would be expected to show behaviour closest to that of an ideal gas?

States of matter

When hydrogen iodide reacts with concentrated sulfuric acid, more than one reaction takes place, including: $8\text{HI} + \text{H}_2\text{SO}_4 \rightarrow \text{H}_2\text{S} + 4\text{H}_2\text{O} + 4\text{I}_2$ Which row shows the change in oxidation number of iodine and sulfur for this reaction?

Electrochemistry

Which statement concerning the Avogadro constant is correct?

Atoms, molecules and stoichiometry

A reaction vessel is charged with 3.60 moles of hydrogen gas and 2.00 moles of iodine vapour, then sealed and kept at a fixed temperature. The reaction is represented by the equation: $\text{H}_2 + \text{I}_2 \rightleftharpoons 2\text{HI}$. When equilibrium is reached, 3.20 moles of hydrogen are still present. Every reactant and product is in the gaseous state. What is the value of $K_p$ for these conditions?

Equilibria

Two chemicals, X and Y, react in solution to produce product Z. The initial rate of formation of product Z was measured in five experiments, 1-5, using different concentrations of X and Y. The results are shown in the table. Which statement is correct?

Reaction kinetics

A sample of $\text{SiCl}_4$ is introduced into cold water. Which statement best describes the mixture present after the reaction has finished?

The Periodic Table: chemical periodicity

L and M are elements from Period 3 in the Periodic Table. • The oxide formed by L is a solid at room temperature. It has a giant structure. • The chloride of L shows no reaction with water. • Of all the elements in Period 3, only argon has a melting point lower than M. Which formula shows a compound made from L and M?

The Periodic Table: chemical periodicity

A farmer needs a solid compound to increase the pH of the soil in a field from $5.5$ to above $6.0$. Which compound might the farmer use?

Equilibria

Z is an anhydrous compound of a Group 2 element. On heating, Z decomposes thermally to form two different gases. Compared with other Group 2 compounds that contain the same anion as Z, it has relatively low thermal stability. What is compound Z?

Group 2

Which row shows mixtures that both lead to the oxidation of a halide ion?

Electrochemistry

Chlorine gas is commonly used to disinfect polluted water. After chlorine is introduced into water, which chemical species present is responsible for killing bacteria?

Equilibria

What environmental consequence can result from the uncontrolled use of nitrate fertilisers?

Nitrogen and sulfur

Ammonia gas, $\text{NH}_3$, together with hydrogen sulfide gas, $\text{H}_2\text{S}$, combine to make the salt ammonium sulfide, $(\text{NH}_4)_2\text{S}$. When ammonium sulfide is dissolved in water, it gives an orange alkaline solution. $(\text{NH}_4)_2\text{S(aq)} \rightleftharpoons \text{NH}_3\text{(aq)} + \text{NH}_4\text{SH(aq)}$ If $\text{NaOH(aq)}$ is added to this solution, a gas, X, is formed. If $\text{HCl(aq)}$ is added to another sample of the solution, a gas, Y, is formed. X and Y may be different gases, or they may be the same gas. What are the identities of X and Y?

Equilibria

Which equation shows the first ionisation energy of iodine?

Atomic structure

Compound P is reacted with excess hydrogen gas in the presence of a nickel catalyst. The resulting product Q is completely saturated. What number of chiral carbon atoms are present in product Q?

Hydrocarbons

Hexadeca-10,12-dien-1-ol is made by silk moths from hexadecanoic acid through a three-stage enzymic process. Which row gives the correct descriptions of these three stages?

Organic synthesis

Compound X can be changed into compound Y in one step. What might X be?

Organic synthesis

Methane and bromine undergo free radical substitution. P and Q take part in the reaction mechanism. P and Q: • act as reactants in propagation steps • act as reactants in termination steps What could P and Q be?

Reaction kinetics

A few drops of 2-bromopropane were added to a test tube. The same volume of aqueous silver nitrate was then introduced. A precipitate was produced. The test was then carried out again using 2-iodopropane. Which row is correct?

Reaction kinetics

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

Halogen compounds

When alcohol X is treated with concentrated sulfuric acid, a mixture of products is formed. Two of these products are structural isomers. What might X be?

Hydroxy compounds

Which reaction would produce a strong organic base?

Equilibria

Which reaction mechanism is correct for the formation of $\text{C}_2\text{H}_5\text{CH(OH)(CN)}$?

An introduction to AS Level organic chemistry

The synthesis route illustrated may be used to produce propan-1-ol. step 1 $\rightarrow$ compound X $\rightarrow$ step 2 Which row shows the reagents that are correct for steps 1 and 2?

Organic synthesis

The structures show three compounds, each containing four carbon atoms in each molecule. Which row gives the correct order from lowest boiling point to highest boiling point?

States of matter

Z has the molecular formula $\text{C}_4\text{H}_8\text{O}$. The infra-red spectrum for Z is shown. What might Z be?

Chemical bonding

Which ions have the same number of electrons as neutrons?

Atomic structure

Compound X is an unbranched hydrocarbon with an $M_r$ of $84$. What can be inferred about X?

Hydrocarbons

When a sample of ammonium chloride is heated, it breaks down to form ammonia and hydrogen chloride gas. $\text{NH}_4\text{Cl}(s) \rightarrow \text{NH}_3(g) + \text{HCl}(g)$ (reaction 1) If the hot ammonia and hydrogen chloride gases come into contact with a cold surface, white ammonium chloride solid is produced again. Which statements are correct?

Equilibria

Hydrogen chloride gas is produced by the reaction below. $\text{H}_2(g) + \text{Cl}_2(g) \rightarrow 2\text{HCl}(g)$ Which change will alter the average kinetic energy of the reacting gas particles?

States of matter

Which oxides will alter the pH when they are added to water?

The Periodic Table: chemical periodicity

By what reaction routes can a pure sample of barium sulfate be made?

Atoms, molecules and stoichiometry

Cortisone is a synthetic hormone. Which class or classes of alcohol are present in this molecule?

Hydroxy compounds

Which changes are usually involved when an addition polymer is formed?

Polymerisation

Which alcohols can be oxidised to produce an organic compound that gives coloured precipitates with both 2,4-dinitrophenylhydrazine reagent and alkaline aqueous iodine?

Hydroxy compounds

The structural formula for alliin is displayed. What are the approximate bond angles $x$, $y$ and $z$ in an alliin molecule?

Chemical bonding

Which of the following mixtures produces a carboxylic acid as one of the products?

Carboxylic acids and derivatives

Flask Q has $5\,\text{dm}^3$ of helium at a pressure of $12\,\text{kPa}$. Flask R has $10\,\text{dm}^3$ of neon at a pressure of $6\,\text{kPa}$. When the flasks are joined together at constant temperature, what will the final pressure be?

States of matter

Sodium chloride, water and air each illustrate one of the three states of matter: solid, liquid and gas. Which row is correct?

States of matter

A reaction pathway diagram is shown for the catalysed and uncatalysed reactions between $\text{N}_2$ and $\text{H}_2$: $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$. Which letter shows the activation energy for the first step in the decomposition of $\text{NH}_3$ in the presence of a catalyst?

Reaction kinetics

Nitrogen and oxygen can combine to produce nitrogen monoxide, NO. $\text{N}_2 + \text{O}_2 \rightarrow 2\text{NO}\quad \Delta H = +180\,\text{kJ mol}^{-1}$. What is the bond energy of the bond between the atoms in NO?

Chemical energetics

This redox equation is given: $\text{SnCl}_2(aq) + 2\text{HgCl}_2(aq) \rightarrow \text{SnCl}_4(aq) + \text{Hg}_2\text{Cl}_2(s)$. Which species undergoes oxidation in this reaction?

Electrochemistry

X is an organic compound whose mass composition is 30.6% carbon, 3.8% hydrogen, 20.4% oxygen and 45.2% chlorine. Calculate the empirical formula of X.

Atoms, molecules and stoichiometry

Nitrogen combines with hydrogen to form ammonia. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ A sealed vessel with a volume of $1\,\text{dm}^3$ contains a mixture of $2.00$ mol of nitrogen, $6.00$ mol of hydrogen and $2.40$ mol of ammonia, and this mixture is left until equilibrium is reached. The equilibrium mixture is then found to contain $2.32$ mol of nitrogen. Which expression could be used to determine the value of $K_c$?

Equilibria

Nitric acid is made by the oxidation of ammonia. In the first stage, ammonia is reacted with oxygen while a catalyst is present, so that nitrogen monoxide is formed. $4\text{NH}_3(g) + 5\text{O}_2(g) \rightleftharpoons 4\text{NO}(g) + 6\text{H}_2\text{O}(g) \quad \Delta H = -1636\ \text{kJ mol}^{-1}$ Which combination of conditions would give the highest equilibrium yield of nitrogen monoxide?

Equilibria

In a Boltzmann distribution, the height of the curve’s peak shows how many molecules possess the most probable energy. A sample of gas is cooled, while the number of molecules stays the same. Which statement correctly describes a feature of the Boltzmann distribution for the gas when the temperature decreases?

Reaction kinetics

Ammonia is composed of simple covalent molecules, $\text{NH}_3$. Ammonia may react with suitable reagents to produce products that contain ammonium ions, $\text{NH}_4^+$. Ammonia may also react with suitable reagents to produce products that contain amide ions, $\text{NH}_2^-$. In an aqueous solution of ammonia, which of these nitrogen-containing species are present?

Equilibria

Which problem may occur if farmers apply too much $\text{NH}_4\text{NO}_3$ to crops?

Nitrogen and sulfur

As you move down Group 17 from chlorine to iodine, which statement is correct?

Group 17

The powder is thought to be either a single sodium halide or a blend of two sodium halides. A portion of the powder was dissolved in water. Aqueous silver nitrate was then added, producing a pale yellow precipitate. When concentrated aqueous ammonia was added after that, part of this precipitate dissolved, leaving a darker yellow precipitate. What might the powder be?

Equilibria

Which of the following statements is correct?

Analytical techniques

A solid, X, was added to an excess of the liquid Y. A colourless gas was evolved and a white precipitate formed. The precipitate was not X. What might X and Y be?

Analytical techniques

Two oxides of Period 3 elements are each placed in water separately. In both cases, colourless solutions are formed. One of the solutions is alkaline, whereas the other is acidic. Which two oxides could they be?

The Periodic Table: chemical periodicity

A $9.61\,\text{g}$ sample of propane, $\text{C}_3\text{H}_8$, is burned completely in excess oxygen at room conditions. What volume of carbon dioxide gas is formed?

Atoms, molecules and stoichiometry

Which compound exhibits stereoisomerism?

Chemical bonding

Two carbon-containing products are formed when alkene Z reacts with a hot, concentrated, acidified solution of potassium manganate(VII). One of the products gives an orange precipitate with 2,4-dinitrophenylhydrazine reagent. The other product is a gas that produces a white precipitate with aqueous calcium hydroxide. Which alkene could be alkene Z?

Hydrocarbons

Which mechanism correctly describes the addition of hydrogen bromide to ethene?

Chemical bonding

Halogenoalkanes are attacked by nucleophiles such as $\text{OH}^-$. Which two halogenoalkanes both undergo an $S_\text{N}1$ mechanism?

Halogen compounds

A blend of ethanol and methanol is burned in oxygen, giving $35\,\text{cm}^3$ of $\text{CO}_2$ and $55\,\text{cm}^3$ of $\text{H}_2\text{O}$. The combustion is complete, and the volumes of both products are recorded at $101\,\text{kPa}$ and $120^\circ\text{C}$. What is the molar ratio, ethanol:methanol, in the mixture?

Atoms, molecules and stoichiometry

The two reactions below are displayed, and in each case only one product has been named. $\text{ethanol} + \text{acidified } \text{Cr}_2\text{O}_7^{2-} \rightarrow \text{ethanal}$ $\text{ethanol} + \text{sodium} \rightarrow \text{sodium ethoxide}$ Which statement concerning these reactions is correct?

Electrochemistry

The skeletal formulae of three compounds, R, S and T, are shown. Which of these compounds would produce a positive result with 2,4-dinitrophenylhydrazine reagent?

Carbonyl compounds

The diagram illustrates the structure of a compound produced when HCN reacts with a carbonyl compound, X. Name the mechanism of this reaction and the functional group present in X?

Carbonyl compounds

Compound Y is reacted with one reagent in suitable conditions. The product formed is 2-methylbutanoic acid. What might compound Y be?

Carboxylic acids and derivatives

Two reactions are depicted. $(\text{CH}_3)_2\text{CHCO}_2\text{H} \xrightarrow{\text{LiAlH}_4} \text{alcohol P}$ $\text{CH}_3\text{CO}_2\text{CH(CH}_3)_2 \xrightarrow{\text{hydrolysis}} \text{alcohol Q} + \text{acid R}$ Which classes of alcohol do P and Q belong to?

Hydroxy compounds

Which atom has the same total number of electrons as an ammonium ion?

Atomic structure

The infra-red spectrum for molecule Z is displayed. What might Z be?

Analytical techniques

Which of the following statements about first ionisation energies are correct?

The Periodic Table: chemical periodicity

This equation represents the breakdown of 3 moles of a chromium-containing ion in acidic solution. $3\text{CrO}_4^{3-}(aq) + 8\text{H}^+(aq) \rightarrow 2\text{CrO}_4^{2-}(aq) + \text{Cr}^{3+}(aq) + 4\text{H}_2\text{O}(l)$ Which of the statements below are correct?

Electrochemistry

Disaccharides undergo hydrolysis in slightly acidic solutions, but the reaction is very slow. A biological catalyst is introduced into a slightly acidic mixture containing three disaccharides: sucrose, maltose and lactose. The hydrolysis reaction is still slow for sucrose and maltose, but it is now much faster for lactose. Which statements about the catalyst are true?

Reaction kinetics

Element X is a solid at room temperature. It is present as an impurity in fossil fuels. When fossil fuels are burnt, its oxide, Y, is produced. In the atmosphere, Y can then be oxidised further to Z. Which statements about X, Y and Z are correct?

Nitrogen and sulfur

Which reagents are used to form a solution of sodium chlorate(V)?

Group 17

Which statements account for the increase in melting point from sodium to aluminium?

Chemical bonding

The diagram depicts a molecule of a compound that is used as a flame retardant. Which of these statements about this structure are correct?

Chemical bonding

Depending on the solvent used, Bromoethane reacts with NaOH in different ways. Which of the following rows about these reactions is correct?

Halogen compounds

Three compounds, X, Y and Z, are shown here. $X$: $\text{C}_2\text{H}_5\text{COCH}_3$, $Y$: $\text{C}_2\text{H}_5\text{CHO}$, $Z$: $\text{CH}_3\text{CO}_2\text{H}$. Which of the following statements about X, Y and Z are correct?

Carbonyl compounds

Ethanal reacts with hydroxylamine, $\text{NH}_2\text{OH}$, to produce the molecule shown. In this structure, what is the order of increasing bond angle, from the smallest to the largest?

Chemical bonding

5-hydroxypentanoic acid is easily converted into the cyclic compound L. Which of the following statements about this reaction are correct?

Equilibria

The bonding present in three substances is described below. substance 1: strong covalent bonds between atoms, permanent dipole-dipole attractions between molecules substance 2: strong covalent bonds between atoms, weak forces between molecules substance 3: strong covalent bonds between atoms, hydrogen bonding between molecules Which compounds could correspond to substances 1, 2 and 3?

Chemical bonding

Which type of bonding is never present in elements?

Chemical bonding

From the information in the table, what is the enthalpy change, $q$, for the reaction shown? $\text{Cs}^+(g) + \text{Br}^-(g) \rightarrow \text{CsBr}(s) \qquad \Delta H = q\,\text{kJ mol}^{-1}$

Chemical energetics

In the enthalpy cycle shown, which enthalpy change does $X$ represent?

Chemical energetics

When copper reacts with dilute nitric acid, it forms a blue solution of $\text{Cu(NO}_3)_2$, together with water and nitrogen(II) oxide as the only products. In the balanced equation, how many moles of acid are needed for three moles of copper?

Atoms, molecules and stoichiometry