Oct/Nov 2018

The table lists the first four ionisation energies for element X. Which ion of X forms when an electron is taken from a filled shell?

Atomic structure

A mixture containing 0.200 mol of sulfur dioxide and 0.200 mol of oxygen is added to a sealed 1.00 dm$^3$ container. The gases are then left to react until equilibrium is established. $ 2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3 $ When equilibrium is reached, the container contains 0.100 mol of $\text{SO}_3$. Calculate the value of $K_c$.

Equilibria

There are two reactions shown below. reaction 1: $ \text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) $ reaction 2: $ 2\text{O}_3(g) \rightleftharpoons 3\text{O}_2(g) $ For reaction 1, a finely powdered iron catalyst is employed. For reaction 2, a vaporised tetrachloromethane catalyst in ultraviolet light is employed. Which statement about the catalysts used is correct?

Reaction kinetics

Sodium and sulfur are each burned separately in oxygen. Each reaction produces a flame of a different colour. Which row is correct?

The Periodic Table: chemical periodicity

X and Y are elements in Period 3 of the Periodic Table. • The oxide of X is solid at room temperature, and this oxide has a giant structure. • The chloride of X does not react with water. • Argon is the only Period 3 element with a melting point lower than that of Y. What might the formula of a compound made between elements X and Y be?

The Periodic Table: chemical periodicity

Which row gives the structure and bonding of $ \text{SiO}_2 $ and $ \text{SiCl}_4 $?

Chemical bonding

A sample of anhydrous calcium nitrate is put into a test-tube and heated strongly in a roaring Bunsen flame until decomposition occurs. The gas present in the test-tube is then described. After that, a glowing splint is introduced into the test-tube and any resulting changes are recorded. Which observations are correct?

Group 2

Which row gives the correct description of the properties of the halogens as Group 17 is descended from chlorine to iodine?

Group 17

Reaction 1: chlorine is reacted with cold aqueous sodium hydroxide, producing solution Z. Reaction 2: solution Z is heated, and $ \text{ClO}_3^- (aq) $ and $ \text{Cl}^- (aq) $ are formed. Which equations show reaction 1 and reaction 2?

Electrochemistry

Which statement accounts for the observation that magnesium hydroxide dissolves in aqueous ammonium chloride, but does not dissolve in aqueous sodium chloride?

Equilibria

Transition elements and their compounds are commonly employed as catalysts. Which element is present in the catalyst used in the Contact process, and what oxidation number does it have?

Chemistry of transition elements

What basic assumption does the kinetic theory make when it is applied to an ideal gas?

States of matter

What characteristic is common to all nucleophiles?

Chemical bonding

X has the molecular formula $ \text{C}_5\text{H}_{12}\text{O} $. X contains a branched carbon skeleton and a secondary alcohol functional group. How many structural isomers match this description of X?

Hydroxy compounds

A new jet fuel has been made and it is a mixture containing different structural isomers of compound Q. The skeletal formula for Q is shown. Which skeletal formula shows a structural isomer of Q?

An introduction to AS Level organic chemistry

The conversion of propene into propan-2-ol may be done in two steps, as shown by the equations below. reaction 1: $\text{CH}_3\text{CH}=\text{CH}_2(g) + \text{HI}(g) \rightarrow \text{CH}_3\text{CHICH}_3(l)$ reaction 2: $\text{CH}_3\text{CHICH}_3(l) + \text{KOH}(aq) \rightarrow \text{CH}_3\text{CH(OH)CH}_3(aq) + \text{K}^+(aq) + \text{I}^- (aq)$ What description is given for these two reactions?

Halogen compounds

An organic molecule W has 3 carbon atoms. It needs 4.5 molecules of oxygen for complete combustion. What might W be?

Atoms, molecules and stoichiometry

Compound J, $\text{C}_{15}\text{H}_{23}\text{Br}_2\text{Cl}$, is treated with an excess of hot concentrated solution of sodium hydroxide in ethanol. One of the products formed is X. What could the skeletal formula of X be?

Halogen compounds

If sodium reacts with $1\ \text{mol}$ of compound Y and produces $1\ \text{mol}$ of $\text{H}_2(g)$, which compound might Y be?

Atoms, molecules and stoichiometry

Which compound exhibits optical isomerism and produces a positive result with alkaline aqueous iodine?

Hydroxy compounds

When ethanedioic acid, $\text{HO}_2\text{CCO}_2\text{H}$, is reduced by an excess of lithium aluminium hydride, $\text{LiAlH}_4$, which organic product is produced?

Carboxylic acids and derivatives

The diester shown can be hydrolysed by heating it with excess aqueous sodium hydroxide. What would be the products of this reaction be?

Carboxylic acids and derivatives

A sample of the hydrocarbon $\text{C}_6\text{H}_{12}$ is burned completely in dry oxygen, and the resulting product gases are gathered as shown. The mass increases of collecting vessels P and Q are $M_P$ and $M_Q$, respectively. What is the value of the ratio $M_P / M_Q$?

Atoms, molecules and stoichiometry

J is a branched-chain alcohol with formula $\text{C}_5\text{H}_{12}\text{O}$. J is heated under reflux with excess $\text{Cr}_2\text{O}_7^{2-}/\text{H}^+$ until the reaction stops changing. An organic product K is obtained in good yield. The infra-red spectrum of K is shown. What are the structures of the branched-chain alcohol J and compound K?

Hydroxy compounds

Which ions possess one or more unpaired electrons?

Atomic structure

Which molecules and ions have bond angles of $120^{\circ}$?

Chemical bonding

Which statements are true for every exothermic reaction?

Chemical energetics

The factors that affect the speed of reaction between aqueous sodium thiosulfate and hydrochloric acid can be studied. The ionic equation for the reaction is shown. $\text{S}_2\text{O}_3^{2-}(aq) + 2\text{H}^+(aq) \rightarrow \text{H}_2\text{O}(l) + \text{S}(s) + \text{SO}_2(aq)$ Which of the following methods can be used to investigate the rate of this reaction?

Reaction kinetics

Which reaction pathways may be used to prepare a pure sample of barium sulfate?

Group 2

Which properties show an increase from magnesium to barium?

Group 2

2-methylpropene can react with chlorine in more than one route. One of these reactions proceeds by the pathway illustrated. Which statements about this mechanism are correct?

Hydrocarbons

The halogenoalkanes shown below each react with $\text{NaOH}(aq)$. Which of these reactions take place mainly by an $S_N1$ mechanism?

Halogen compounds

3-oxobutanoic acid may be made in a two-step sequence. $X \rightarrow Y \rightarrow$ 3-oxobutanoic acid What might the structure of $X$ be?

Organic synthesis

Samples of 5.0 g of the carbonates of barium, copper, lithium and magnesium are heated so that they decompose into the metal oxides and carbon dioxide. Which compound shows the greatest loss in mass?

Atoms, molecules and stoichiometry

Ethanal reacts with HCN in the presence of KCN. What bond changes take place in this reaction?

Chemical bonding

For this question, assume that methane behaves as an ideal gas. The gas laws are represented by the ideal gas equation shown below. $pV = nRT$ A sample of methane has a measured volume at a temperature of $60\,^{\circ}\text{C}$ and a pressure of $103\,\text{kPa}$. The recorded volume is $5.37 \times 10^{-3}\,\text{m}^3$. Calculate the mass of the methane sample, correct to two significant figures.

States of matter

A butane burner is used to warm water. The $M_r$ of butane is 58. • $\Delta H_c^{\circ}$ of butane is $-2877\,\text{kJ mol}^{-1}$. • $250\,\text{g}$ of water is heated from $12\,^{\circ}\text{C}$ to $100\,^{\circ}\text{C}$. • The burner transfers $47\%$ of the heat released from the burning fuel to the water. Assume that the butane undergoes complete combustion and none of the water evaporates. What mass of butane must be burnt at minimum?

Chemical energetics

Nitric acid is recognised as being involved in the oxidation of sulfur dioxide in the atmosphere. One possible reaction is given below. $\text{SO}_2 + \text{HNO}_3 \rightarrow \text{NO}^+ + \text{HSO}_4^-$ Which row gives the correct changes in oxidation numbers for nitrogen and sulfur?

Electrochemistry

A transition metal ion, $\text{M}^{2+}$, is oxidised by acidified dichromate(VI) ions to give $\text{M}^{4+}$ ions, $\text{Cr}^{3+}$ ions, and $\text{H}_2\text{O}$. Which equation shows this reaction correctly?

Electrochemistry

For this question, assume that every gas behaves ideally. Hydrogen and iodine undergo a reversible reaction shown below. The mixture attains dynamic equilibrium. $\text{H}_2(\text{g}) + \text{I}_2(\text{g}) \rightleftharpoons 2\text{HI}(\text{g}) \qquad \Delta H = -9.5\,\text{kJ mol}^{-1}$ Which statement must be correct for the $K_p$ of this equilibrium to remain constant?

Equilibria

Which of these statements about enthalpy changes is correct?

Chemical energetics

In a chemical system, the particles present have a spread of energies. This can be represented on a graph known as the Boltzmann distribution. Which statement correctly describes the effect of a catalyst on the particles in a chemical system?

Reaction kinetics

Nitrogen and hydrogen may react to produce ammonia. This reaction is exothermic. The rate and yield of the reaction can be changed by altering the conditions used for the reaction. Which row indicates the effects of adding iron to the mixture and raising the temperature?

Equilibria

For the Period 3 elements from phosphorus to argon, the table lists these melting points: P $317\,\text{K}$, S $392\,\text{K}$, Cl $172\,\text{K}$, Ar $84\,\text{K}$. Which factor is responsible for the changes in melting points from phosphorus to argon?

The Periodic Table: chemical periodicity

What observations are seen when a sample of silicon chloride, $\text{SiCl}_4$, is added into a beaker of water?

The Periodic Table: chemical periodicity

A $4.00\,\text{g}$ portion of an anhydrous Group 2 metal nitrate is heated strongly until its mass no longer changes. This leaves a solid residue with a mass of $1.37\,\text{g}$. Which metal is present?

Atoms, molecules and stoichiometry

Which row contains only correct comparisons of magnesium and barium?

Group 2

Which of the following statements about the halogens is correct?

Group 17

When chlorine reacts with sodium hydroxide, the reaction can occur with either cold or hot conditions to give chlorine-containing products. If cold sodium hydroxide gives sodium chlorate($X$), and hot sodium hydroxide gives sodium chlorate($Y$), where $X$ and $Y$ are oxidation numbers, which equation is correct?

Electrochemistry

In the Contact process, the product formed is $Z$. Which reaction or process produces a gas able to neutralise an aqueous solution of $Z$?

Equilibria

When ammonium cyanate is heated with air excluded, the reaction gives only urea, $\text{CO(NH}_2)_2$. No other products are produced in this reaction. What is the formula of the cyanate ion in ammonium cyanate?

Atoms, molecules and stoichiometry

An electrical field deflects beams of charged particles. The deflection angle of a particle is proportional to its charge / mass ratio. In one experiment, protons are deflected through an angle of $+15^{\circ}$. In a separate experiment carried out under identical conditions, $^2_1\text{H}^+$ ions are deflected through an angle of $Y^{\circ}$. What is the value of $Y$?

Atomic structure

There are three structural isomers that have the formula $\text{C}_5\text{H}_{12}$. Which formulae correctly show these three structural isomers?

Hydrocarbons

The diagram depicts a molecule containing $\sigma$ bonds and $\pi$ bonds: $\text{CH}_2{=}\text{CH-CH}_2-\text{C(=O)-O-CH}_2-\text{CH{=}CH}_2$. What is the number of $\sigma$ bonds in this molecule?

Chemical bonding

Polyethene is produced through the polymerisation of ethene. Which statement is correct?

Polymerisation

Compound $P$ undergoes separate reactions with $\text{KOH(aq)}$ and with $\text{HBr}$. Compound $P$ has the formula $\text{CH}_2\text{CHCH}_2\text{CH}_2\text{Cl}$. What are the mechanisms of these two reactions?

Chemical bonding

Which statement correctly describes compound Q? Compound Q has the structure $\text{CH}_3\text{C}=\text{CHCH}_2\text{CH}_3$ with a $\text{CO}_2\text{CH}_3$ group attached to the carbon in the double bond.

Hydrocarbons

A halogenoalkane has the molecular formula $\text{C}_5\text{H}_{11}\text{Br}$. When it is heated with ethanolic sodium hydroxide, no alkene is produced. Which halogenoalkane could it be?

Halogen compounds

The table lists the reactions of four organic compounds. Which one could be propan-2-ol?

Hydroxy compounds

Compound X has the empirical formula $\text{C}_2\text{H}_3\text{O}$. When Compound X is treated with 2,4-dinitrophenylhydrazine reagent, an orange precipitate is formed, and it also decolourises warmed acidified potassium manganate(VII) solution. What could X be?

Carbonyl compounds

When Compound Y is treated with aqueous sodium hydroxide, methanol and sodium ethanoate are formed. What is the structure of Y?

Carboxylic acids and derivatives

Which compound can be converted into propanoic acid by using just one reagent?

Organic synthesis

Rubidium and bromine form ions that are isoelectronic. Each ion contains $36$ electrons. Which row is the correct one?

Atomic structure

The infra-red spectrum of compound L is displayed. What might the structure of L be?

Analytical techniques

Zinc reacts with hydrochloric acid according to the equation shown below: $\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2$ Which of the statements below are correct?

Atoms, molecules and stoichiometry

The melting point of chlorine is lower than the melting point of iodine. Which statements can be used to explain this difference?

States of matter

Aqueous iron(II) sulfate is able to participate in redox reactions. $6\text{FeSO}_4 + 7\text{H}_2\text{SO}_4 + \text{Na}_2\text{Cr}_2\text{O}_7 \\rightarrow 3\text{Fe}_2(\text{SO}_4)_3 + \text{Cr}_2(\text{SO}_4)_3 + \text{Na}_2\text{SO}_4 + 7\text{H}_2\text{O}$ Which redox changes take place in this reaction?

Electrochemistry

This equation shows an equilibrium. $4\text{NH}_3(g) + 5\text{O}_2(g) \rightleftharpoons 4\text{NO}(g) + 6\text{H}_2\text{O}(g) \qquad \Delta H = -900\ \text{kJ mol}^{-1}$ Which change would raise the concentration of NO at equilibrium?

Equilibria

A sample with $x$ mol of $\text{Al}_2\text{Cl}_6$ is mixed with water to form solution W. To precipitate all the aluminium as its hydroxide, $y$ mol of sodium hydroxide are needed. Further alkali is then introduced to dissolve the precipitate again, producing solution Z. Which of the following statements are correct?

Equilibria

Which statements regarding calcium hydroxide are correct?

Group 2

Which of these bromopropenes would be expected to react with cold bromine in the dark to produce a product that has a chiral carbon atom?

Hydrocarbons

Halogenoalkanes can react with hydroxide ions. $\text{RBr} + \text{OH}^- \rightarrow \text{ROH} + \text{Br}^-$ Some halogenoalkanes react via the $\mathrm{S_N1}$ mechanism. Which of the statements about the $\mathrm{S_N1}$ mechanism are correct?

Halogen compounds

Which of the following statements about 2-methylbutan-1-ol are correct?

Hydroxy compounds

In which set are all the molecules arranged so that all their atoms lie in a single plane?

Chemical bonding

cis-hex-3-enal is the compound that produces the characteristic smell of cut grass. Which reagents can react with cis-hex-3-enal?

An introduction to AS Level organic chemistry

Flask X holds $5\,\text{dm}^3$ of helium at a pressure of $12\,\text{kPa}$, while flask Y holds $10\,\text{dm}^3$ of neon at a pressure of $6\,\text{kPa}$. If the flasks are joined together at constant temperature, what is the final pressure?

States of matter

An exact mass of $1.00\,\text{g}$ of a metallic element reacts fully with $300\,\text{cm}^3$ of oxygen at $298\,\text{K}$ and $1\,\text{atm}$ pressure, producing an oxide containing $\text{O}^{2-}$ ions. At this temperature and pressure, one mole of gas occupies $24.0\,\text{dm}^3$. Which metal could this be?

Atoms, molecules and stoichiometry

Ethanol is being used more and more as a fuel in cars. The standard enthalpy change of formation of carbon dioxide is $-393\,\text{kJ mol}^{-1}$. The standard enthalpy change of formation of water is $-286\,\text{kJ mol}^{-1}$. The standard enthalpy change of formation of ethanol is $-277\,\text{kJ mol}^{-1}$. Calculate the standard enthalpy change of combustion of ethanol.

Chemical energetics

Ammonium metavanadate, $\text{NH}_4\text{VO}_3$, may be used to prepare a solution of $\text{VO}_2\text{Cl}$, which contains chloride ions. What is the change in vanadium's oxidation number in this reaction?

Electrochemistry

For this question, every pressure is given in atm. The following equation shows the equilibrium for three gaseous species X, Y and Z. $\text{X} + 3\text{Y} \rightleftharpoons 2\text{Z}$ At temperature $T_1$, the numerical value of $K_p$, the equilibrium constant, is $2$. When the temperature is increased to $T_2$, the equilibrium partial pressures are listed below. $X = 2$, $Y = 3$, $Z = 5$ Which row is correct?

Equilibria

The table shows the first four ionisation energies for element X. Which ion of X is formed when an electron is removed from a filled shell?

Atomic structure

A sealed container with a volume of $1.00\,\text{dm}^3$ initially contains 0.200 mol of sulfur dioxide and 0.200 mol of oxygen. The gases are left to react until equilibrium is established. $\text{2SO}_2 + \text{O}_2 \rightleftharpoons \text{2SO}_3$ When equilibrium is reached, the amount of $\text{SO}_3$ in the container is $0.100$ mol. Calculate the value of $K_c$.

Equilibria

The two reactions below are given. Reaction 1: $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ Reaction 2: $2\text{O}_3(g) \rightleftharpoons 3\text{O}_2(g)$ For reaction 1, a finely divided iron catalyst is used. For reaction 2, a vapourised tetrachloromethane catalyst in ultraviolet light is used. Which statement concerning the catalysts used is correct?

Reaction kinetics

Sodium and sulfur are each burned separately in oxygen. Each reaction produces a flame with a different colour. Which row gives the correct answer?

The Periodic Table: chemical periodicity

X and Y are elements in Period 3 of the Periodic Table. • The oxide of X is a solid at room temperature, and this oxide has a giant structure. • The chloride of X does not react with water. • Argon is the only element in Period 3 that has a lower melting point than Y. What might be the formula of a compound made between X and Y?

The Periodic Table: chemical periodicity

Which row gives the structure and bonding of $\text{SiO}_2$ and $\text{SiCl}_4$?

Chemical bonding

A sample of anhydrous calcium nitrate is put into a test-tube and heated in a roaring Bunsen flame until it breaks down. The gas in the test-tube is then observed. A glowing splint is then inserted into the test-tube and any changes are recorded. Which observations are correct?

Nitrogen and sulfur

Which row correctly shows the properties of the halogens when Group 17 is descended from chlorine to iodine?

Group 17

Reaction 1: chlorine is added to cold aqueous sodium hydroxide to give solution Z. Reaction 2: solution Z is heated and produces $\text{ClO}_3^-(aq)$ and $\text{Cl}^-(aq)$. Which equations match reaction 1 and reaction 2?

Electrochemistry

Which statement accounts for the fact that magnesium hydroxide dissolves in aqueous ammonium chloride, but does not dissolve in aqueous sodium chloride?

Equilibria

Transition elements, together with their compounds, are frequently used as catalysts. What is the identity, and what is the oxidation number, of the element in the catalyst used in the Contact process?

The Periodic Table: chemical periodicity

What fundamental assumption does the kinetic theory make when it is applied to an ideal gas?

States of matter

Which statement is true for every nucleophile?

Chemical bonding

X is described by the molecular formula $\text{C}_5\text{H}_{12}\text{O}$. X contains a branched carbon skeleton and a secondary alcohol functional group. How many structural isomers match this description of X?

Hydroxy compounds

A new jet fuel has been made from a blend of different structural isomers of compound Q. Which skeletal formula shows a structural isomer of Q?

Chemical bonding

Propene may be changed into propan-2-ol in two steps, as set out by the equations below. reaction 1: $\text{CH}_3\text{CH}=\text{CH}_2\text{(g)} + \text{HI(g)} \rightarrow \text{CH}_3\text{CHICH}_3\text{(l)}$ reaction 2: $\text{CH}_3\text{CHICH}_3\text{(l)} + \text{KOH(aq)} \rightarrow \text{CH}_3\text{CH(OH)CH}_3\text{(aq)} + \text{K}^+\text{(aq)} + \text{I}^-\text{(aq)}$ In what way can these two reactions be classified?

Halogen compounds

Organic compound W has 3 carbon atoms. It needs $4.5$ molecules of oxygen to undergo complete combustion. What might W be?

Hydrocarbons

Compound J, $\text{C}_{15}\text{H}_{23}\text{Br}_2\text{Cl}$, is treated with an excess of hot, concentrated sodium hydroxide in ethanol. One product formed is X. Which skeletal formula could represent X?

Halogen compounds

Sodium reacts with $1$ mol of compound Y to form $1$ mol of $\text{H}_2\text{(g)}$. Which compound could Y be?

Atoms, molecules and stoichiometry

Of the compounds listed, which one displays optical isomerism and also produces a positive test in alkaline aqueous iodine?

Hydroxy compounds

Ethanedioic acid, $\text{HO}_2\text{CCO}_2\text{H}$, is reduced with an excess of lithium aluminium hydride, $\text{LiAlH}_4$. Which organic product is formed in the reaction?

Carboxylic acids and derivatives

The diester displayed may be hydrolysed by heating it with excess aqueous sodium hydroxide. What products are formed in this reaction?

Carboxylic acids and derivatives

A specimen of the hydrocarbon $\text{C}_6\text{H}_{12}$ is burned completely in dry oxygen, and the resulting product gases are collected as shown. The increases in mass of the collecting vessels P and Q are $M_p$ and $M_q$, respectively. Determine the ratio $M_p / M_q$?

Atoms, molecules and stoichiometry

J is a branched-chain alcohol with formula $\text{C}_5\text{H}_{12}\text{O}$. It is heated under reflux with excess $\text{Cr}_2\text{O}_7^{2-}/\text{H}^+$ until the reaction is complete. A compound K is obtained in good yield. The infra-red spectrum of K is shown. What are the structures of the branched-chain alcohol J and compound K?

Hydroxy compounds

Which ions have one or more unpaired electrons?

Atomic structure

Which molecules and ions have bond angles of $120^\circ$?

Chemical bonding

For every exothermic reaction, which statements are correct?

Chemical energetics

The factors that influence the rate of reaction between aqueous sodium thiosulfate and hydrochloric acid may be studied. The ionic equation for the reaction is shown. $\text{S}_2\text{O}_3^{2-}(aq) + 2\text{H}^+(aq) \rightarrow \text{H}_2\text{O}(l) + \text{S}(s) + \text{SO}_2(aq)$ Which of the following is suitable for investigating the rate of this reaction?

Reaction kinetics

Which reaction pathways can be used to obtain a pure sample of barium sulfate?

Group 2

Which properties show an increase from magnesium to barium?

Group 2

$2$-methylpropene may react with chlorine in more than one manner. One of these reactions proceeds by the pathway illustrated. Which of the following statements about this mechanism are correct?

Reaction kinetics

The halogenoalkanes shown below each react with $\text{NaOH}(aq)$. Which of the reactions occurs mainly by an $\text{S}_\text{N}1$ mechanism?

Halogen compounds

$3$-oxobutanoic acid may be prepared in a two-step route. $X \rightarrow Y \rightarrow \text{3-oxobutanoic acid}$ What might the structure of $X$ be?

Organic synthesis

When 5.0 g samples of the carbonates of barium, copper, lithium and magnesium are broken down into the corresponding metal oxides and carbon dioxide, which compound shows the largest decrease in mass?

Atoms, molecules and stoichiometry

Ethanal reacts with $\text{HCN}$ in the presence of $\text{KCN}$. Which bonding changes take place in this reaction?

Chemical bonding

For this question, assume that methane acts as an ideal gas. The gas laws are summarised by the ideal gas equation $pV = nRT$. A methane sample has its volume measured at $60\,^{\circ}\text{C}$ and a pressure of $103\,\text{kPa}$. The measured volume is $5.37 \times 10^{-3}\,\text{m}^3$. What is the mass of the methane sample, to two significant figures?

States of matter

A butane burner is being used to heat water. The $M_r$ for butane is 58. The $\Delta H_c^\circ$ of butane is $-2877\,\text{kJ mol}^{-1}$. A mass of $250\,\text{g}$ of water is warmed from $12\,^{\circ}\text{C}$ up to $100\,^{\circ}\text{C}$. The burner passes $47\%$ of the heat released by the burning fuel to the water. Assume that the butane burns completely and that no water evaporates. What is the minimum mass of butane that has to be burnt?

Chemical energetics

Nitric acid is understood to be involved in the oxidation of sulfur dioxide in the atmosphere. One possible reaction is given as: $\text{SO}_2 + \text{HNO}_3 \rightarrow \text{NO}^+ + \text{HSO}_4^-$. Which row gives the correct changes in oxidation numbers for nitrogen and sulfur?

Electrochemistry

A transition metal ion, $M^{2+}$, is oxidised by acidified dichromate(VI) ions to produce $M^{4+}$ ions, $\text{Cr}^{3+}$ ions and $\text{H}_2\text{O}$. Which equation shows this reaction correctly?

Electrochemistry

For this question, assume that all gases behave ideally. Hydrogen and iodine react reversibly in the reaction shown below. The system then attains dynamic equilibrium. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$ $\Delta H = -9.5\,\text{kJ mol}^{-1}$. Which statement must be true for the $K_p$ of this equilibrium to be constant?

Equilibria