Oct/Nov 2019

The diagram illustrates the Boltzmann distribution for the energies of particles in a gas. This gas takes part in a reaction with an activation energy, $E_a$. The highest point on the curve is marked $P$. If the same reaction is done in the presence of a catalyst, which statement is correct?

Reaction kinetics

Compounds X and Y react to form compound Z. This reaction is reversible. $X + Y \rightleftharpoons Z$ When X and Y are placed together in a closed system, a dynamic equilibrium is slowly established. Which graph could show how the rates of the forward and reverse reactions change with time?

Equilibria

The reaction of sulfur dioxide with oxygen is reversible. $\text{2SO}_2(g) + \text{O}_2(g) \rightleftharpoons \text{2SO}_3(g)$ $K_c = 280\ \text{mol}^{-1}\ \text{dm}^3$ at $1000\ \text{K}$ For an equilibrium mixture at $1000\ \text{K}$, the concentration of sulfur dioxide is $0.200\ \text{mol dm}^{-3}$ and the concentration of oxygen is $0.100\ \text{mol dm}^{-3}$. Determine the concentration of sulfur trioxide.

Equilibria

Which oxide will raise the pH when it is added to water?

The Periodic Table: chemical periodicity

X, Y and Z are three neighbouring elements in Period 3 of the Periodic Table. Element Y has the highest first ionisation energy and the lowest melting point of the three. What are the identities of X, Y and Z?

The Periodic Table: chemical periodicity

When a $5.00\ \text{g}$ sample of an anhydrous Group 2 metal nitrate is heated strongly, its mass falls by $3.29\ \text{g}$. Which metal is present?

Atoms, molecules and stoichiometry

Solutions P and Q each contain a different Group 2 ion at equal concentration. One has $\text{Mg}^{2+}$, whereas the other has $\text{Ba}^{2+}$. Separate $5\ \text{cm}^3$ portions of P and Q are tested. test 1: add $1\ \text{cm}^3$ of $0.1\ \text{mol dm}^{-3}\ \text{Na}_2\text{SO}_4(aq)$ test 2: add $1\ \text{cm}^3$ of $0.1\ \text{mol dm}^{-3}\ \text{NaOH}(aq)$ What outcomes would these tests give?

Equilibria

Chlorine and bromine differ in their volatilities. Which row names the more volatile element and gives the correct explanation?

States of matter

Sodium azide, $\text{NaN}_3$, is dissolved in water. Acidified silver nitrate is then added to the solution, producing a white precipitate. After that, aqueous ammonia is added to the white precipitate. The azide ion, $\text{N}_3^-$, shows chemical behaviour similar to the $\text{Cl}^-$ ion. Which row in the table could be predicted from this information?

Analytical techniques

What type of reaction takes place when solid ammonium sulfate is heated with an excess of sodium hydroxide solution?

Nitrogen and sulfur

Many cars have catalytic converters installed in their exhaust systems. Which gas: - leads to acid rain when it is released into the atmosphere - is taken out of car exhaust fumes by a catalytic converter?

Reaction kinetics

Diamond consists of carbon in pure form. A diamond’s mass can be measured in carats. One carat is $0.200\,\text{g}$ of carbon. Which expression gives the number of carats that contain $6.02 \times 10^{23}$ carbon atoms?

Atoms, molecules and stoichiometry

Which substance reacts with trichloroethene in order to produce a chiral product?

Hydrocarbons

Alkanes are saturated hydrocarbons. What type of reaction are alkanes most likely to undergo?

Hydrocarbons

An alkene is reacted with hot, concentrated, acidified potassium manganate(VII), giving one organic product, as illustrated. hot, concentrated, acidified $\text{KMnO}_4(aq)$ Which alkene structure would produce this product?

Hydrocarbons

A tertiary bromoalkane, represented here by $>\!\text{C--Br}$, undergoes reaction with aqueous $\text{NaOH}$. The mechanism follows the pathway illustrated. Which point on the diagram is labelled correctly?

Halogen compounds

Bromoethane and chloroethane are each mixed with water in separate tests. Hydrolysis takes place. Which compound undergoes hydrolysis more quickly, and what is the mechanism?

Halogen compounds

When alcohol X is oxidised, compound Y is formed. Y has a composition of $54.54\%$ carbon, $36.36\%$ oxygen and $9.10\%$ hydrogen. The $M_r$ of Y is $88.0$. What structure could alcohol X have?

Atoms, molecules and stoichiometry

The diagram depicts the structure of compound Z. What product is formed in the reaction of compound Z with an excess of $\text{NaBH}_4$?

Carbonyl compounds

Compound Q has these test results: with 2,4-dinitrophenylhydrazine, an orange precipitate forms; with Fehling’s reagent, a red-brown precipitate is produced; and with alkaline aqueous iodine, a pale yellow precipitate appears. What is the identity of Q?

Carbonyl compounds

Many plants contain tartaric acid, $\text{HO}_2\text{CCH(OH)CH(OH)CO}_2\text{H}$. When a sample of tartaric acid is treated with an excess of $\text{LiAlH}_4$, the organic product J is formed. What is observed when $\text{NaOH(aq)}$ is added to separate samples of tartaric acid and J?

Equilibria

When $\text{CH}_2(\text{OH})\text{CH=CHCO}_2\text{H}$ is heated with a small amount of concentrated sulfuric acid, it produces a cyclic compound. What is the skeletal formula of this cyclic compound?

Chemical bonding

Which molecule or ion has the smallest bond angle?

Chemical bonding

The infra-red spectrum for compound P is shown. Which substance could compound P be?

Chemical bonding

A germanium atom, Ge, with nucleon number $70$ is considered. Which of the following statements about the $^{{70}}_{{32}}\text{Ge}$ atom are correct?

Atomic structure

The first ionisation energy of chlorine is higher than the first ionisation energy of sulfur. Which of these factors account for this?

The Periodic Table: chemical periodicity

Liquids X and Y do not react with each other. Their boiling points are the same. When a certain volume of X is shaken with an equal volume of Y, they produce a liquid mixture Z. The mean intermolecular forces in liquid Z are stronger than the mean forces in X and the mean forces in Y. Which deductions drawn from this information are correct?

States of matter

The equation below shows the stoichiometry of a catalysed reaction. $\text{P(g)} + \text{Q(g)} \rightleftharpoons \text{R(g)} + \text{S(l)}$ In two experiments, the amount of R is measured. The outcomes are shown in the diagram. Which changes in the conditions could account for the results shown?

Equilibria

Which of the following statements are correct?

Atoms, molecules and stoichiometry

Nitrogen gas is not very reactive, whereas oxygen gas and chlorine gas react more easily. Which statements help to explain this difference?

Chemical bonding

The structure of tiglic acid is $\text{CH}_3\text{CH} = \text{C(CH}_3)\text{CO}_2\text{H}$. Which of these statements about the properties of a single molecule of this acid are correct?

Chemical bonding

Which compounds, when heated with an excess of concentrated sulfuric acid, form only one product with molecular formula $\text{C}_7\text{H}_{10}$?

Hydroxy compounds

Hydrogen cyanide reacts with propanone in the presence of potassium cyanide. Which statements about this reaction are correct?

Carbonyl compounds

The four compounds listed are $\text{C}_2\text{H}_4$, $\text{C}_2\text{H}_5\text{OH}$, $\text{CH}_3\text{CHO}$, and $\text{CH}_3\text{CO}_2\text{H}$. For how many of these compounds is the number of $\sigma$ bonds odd?

Chemical bonding

Which compounds give rise to three distinct organic products after hydrolysis?

Carboxylic acids and derivatives

Ethanal, $\text{CH}_3\text{CHO}$, ethanol, $\text{C}_2\text{H}_5\text{OH}$, and methoxymethane, $\text{CH}_3\text{OCH}_3$, are three organic compounds. Which of these compounds has the greatest boiling point, and which interaction is responsible for this boiling point being the greatest?

States of matter

What oxidation number does sulfur have in each species?

Electrochemistry

The information below is required for this question. $\Delta H_f^\circ(\text{N}_2\text{H}_4(\ell)) = 50.6\,\text{kJ mol}^{-1}$, $\Delta H_f^\circ(\text{N}_2\text{O}_4(\text{g})) = 9.2\,\text{kJ mol}^{-1}$, $\Delta H_f^\circ(\text{H}_2\text{O}(\text{g})) = -241.8\,\text{kJ mol}^{-1}$. Hydrazine, $\text{N}_2\text{H}_4(\ell)$, combines with dinitrogen tetraoxide, $\text{N}_2\text{O}_4(\text{g})$, producing nitrogen gas and water vapour: $2\text{N}_2\text{H}_4(\ell) + \text{N}_2\text{O}_4(\text{g}) \rightarrow 3\text{N}_2(\text{g}) + 4\text{H}_2\text{O}(\text{g})$. What is the enthalpy change for this reaction?

Chemical energetics

When sodium reacts with oxygen, heat energy is released and the compound $\text{Na}_2\text{O}$ is formed. The reaction equation is shown here: $2\text{Na}(\text{s}) + \tfrac{1}{2}\text{O}_2(\text{g}) \rightarrow \text{Na}_2\text{O}(\text{s})$. Which statement about this reaction is correct?

Chemical energetics

In this chemical equation, $w$, $x$, $y$, and $z$ each represent whole numbers. $w\text{ClO}_3^- + x\text{MnO}_4^- + y\text{H}^+ \rightarrow w\text{ClO}_4^- + x\text{MnO}_2 + z\text{H}_2\text{O}$. Once the equation has been balanced, what are $w$, $x$ and $y$?

Electrochemistry

The diagram illustrates a Boltzmann distribution for the energies of gaseous molecules together with the activation energies, $E_a$, for a reaction both in the absence of a catalyst and in the presence of a catalyst. Which statement about this distribution curve is correct?

Reaction kinetics

The decomposition of $\text{SO}_3(g)$ forms a dynamic equilibrium. $\text{2SO}_3(g) \rightleftharpoons \text{2SO}_2(g) + \text{O}_2(g)$ What effect does increasing the pressure of the system have?

Equilibria

The following reaction occurs for hydrated aluminium ions. $[\text{Al(H}_2\text{O)}_6]^{3+}(aq) + \text{H}_2\text{O}(l) \rightleftharpoons [\text{Al(H}_2\text{O)}_5\text{OH}]^{2+}(aq) + \text{H}_3\text{O}^+(aq)$ Which statement is true about this reaction?

Equilibria

Which diagram correctly displays the electronegativity values of the elements Na, Mg, Al and Si plotted against their first ionisation energies?

The Periodic Table: chemical periodicity

Which statement concerning the compounds of Group 2 elements magnesium to barium is correct?

Group 2

When equal volumes of saturated barium hydroxide solution and calcium hydroxide solution are combined, a white precipitate, Y, is formed. The mixture is then filtered, and carbon dioxide is passed through the filtrate, giving a second white precipitate, Z. What are Y and Z?

Equilibria

During the redox reaction of chlorine with hot aqueous sodium hydroxide, chlorate(V) ions, $\text{ClO}_3^-$, are formed. Oxidation numbers may be used to help in balancing the equation for this reaction. $v\text{Cl}_2(g) + w\text{OH}^-(aq) \rightarrow x\text{Cl}^-(aq) + y\text{ClO}_3^-(aq) + z\text{H}_2\text{O}(l)$ State the values of v, x and y in the balanced equation.

Electrochemistry

The characteristics of chlorine, bromine and the compounds they form are being compared. Which characteristic is lower for chlorine than for bromine?

Group 17

When solid sodium iodide is treated with concentrated sulfuric acid, more than one sulfur-containing product is produced. What is the smallest oxidation number of sulfur in these products?

Group 17

Which emission released by an internal combustion engine causes marble statues to erode?

Nitrogen and sulfur

Ammonia, carbon dioxide and water combine to produce ammonium carbonate. Which statement concerning this reaction is correct?

Nitrogen and sulfur

For this question, assume that $(\text{NH}_4)_2\text{CO}_3·\text{H}_2\text{O}(s)$ dissolves in water with no change in volume. What mass of $(\text{NH}_4)_2\text{CO}_3·\text{H}_2\text{O}(s)$ must be added to $800\,\text{cm}^3$ of water to produce a $0.100\,\text{mol dm}^{-3}$ solution of $\text{NH}_4^+$ ions?

Atoms, molecules and stoichiometry

When answering this question, take structural isomerism and stereoisomerism into account. How many isomers with the formula $\text{C}_5\text{H}_{10}$ have structures containing $\pi$ bonding?

Hydrocarbons

The diagram illustrates the skeletal formula for phenazine. What is the empirical formula of phenazine?

Atoms, molecules and stoichiometry

An organic compound X is treated with hot, concentrated acidified potassium manganate(VII) solution and produces only one carbon-containing product. What could X be?

An introduction to AS Level organic chemistry

In ethanol, 1-chloro-2-methylbutane undergoes nucleophilic substitution with sodium cyanide. Which intermediate or transition state is most likely to be formed in this reaction?

Reaction kinetics

Propan-1-ol may be treated with acidified potassium dichromate(VI) to produce propanoic acid in reaction 1, or propanal in reaction 2. How can the reaction be done so that reaction 2 takes place instead of reaction 1?

Electrochemistry

What is the least amount of oxygen molecules required for the complete combustion of $40.0\,\text{g}$ of methanol?

Atoms, molecules and stoichiometry

Compound $X$ shows stereoisomerism and produces a precipitate on warming with Fehling’s reagent. What is the possible structure of compound $X$?

Carbonyl compounds

The diagram illustrates the structure of $Y$. Two statements are given about $Y$: 1. $Y$ can be oxidised by hot, acidified dichromate(VI) ions. 2. When $Y$ reacts with an excess of alkaline aqueous iodine, one mole of $Y$ yields one mole of tri-iodomethane. Which of these statements are correct?

Carbonyl compounds

Esters may be formed by reacting a carboxylic acid with an alcohol in the presence of concentrated sulfuric acid. Which row shows the correct names of the reagents that would be suitable for making ester $Z$?

Carboxylic acids and derivatives

Compound $Q$ may be hydrolysed using $\text{HCl(aq)}$. The two products formed by this hydrolysis share the same empirical formula. What could $Q$ be?

Carboxylic acids and derivatives

The graph displays the successive ionisation energies of element X and element Y. Both elements belong to Period 3. Which statement is right?

The Periodic Table: chemical periodicity

Analysis of substance $T$ showed that it contained $62.07\%$ carbon, $10.34\%$ hydrogen and $27.59\%$ oxygen. The infra-red spectrum for substance $T$ is shown. Which substance might $T$ be?

Atoms, molecules and stoichiometry

Which gaseous molecules show polarity?

Chemical bonding

In a carbon monoxide molecule, CO, there are three bonds joining the carbon atom to the oxygen atom. Which of the following features occur in one CO molecule?

Chemical bonding

Carbon may occur as allotropes, including graphite, diamond and a fullerene. Which of the following statements are correct?

Chemical bonding

A reaction pathway diagram for a reversible reaction is given. Which statements are correct?

Chemical energetics

Silicon can form a tetrachloride, $\text{SiCl}_4$. Which of the statements below are correct?

Chemical bonding

Which of the following statements about ammonia are correct?

Nitrogen compounds

Once crude oil has been separated by fractional distillation, which process can be used to make propene from larger hydrocarbon molecules?

Hydrocarbons

Bromoethane undergoes nucleophilic substitution reactions. Which of the following statements are accurate?

Halogen compounds

Which reagents, if they are in excess, could convert Y into Z? $\text{CH}_3\text{CH(OH)CO}_2\text{H} \rightarrow \text{CH}_3\text{CH(OH)CO}_2\text{Na}$

Carboxylic acids and derivatives

Which statement correctly describes the electrons in a carbon atom in the ground state?

Atomic structure

Each compound shown below is reacted on its own with excess NaBH$_4$. The product from each reaction is then heated with excess concentrated $\text{H}_2\text{SO}_4$. Which compounds produce just one final product with molecular formula $\text{C}_7\text{H}_{10}$?

Carbonyl compounds

For this question, assume that the vapour acts as an ideal gas. $0.175\,\text{g}$ of a volatile liquid forms a vapour with volume $4.50 \times 10^{-5}\,\text{m}^3$ at $100\,^\circ\text{C}$ and pressure $1.013 \times 10^5\,\text{Pa}$. Determine the $M_r$ of the liquid.

Atoms, molecules and stoichiometry

Which reaction is described as endothermic?

Chemical energetics

Which equation correctly shows the standard enthalpy change of atomisation for the element given?

Chemical energetics

$(\text{NH}_4)_2\text{Cr}_2\text{O}_7$ breaks down on heating. $(\text{NH}_4)_2\text{Cr}_2\text{O}_7 \rightarrow \text{N}_2 + 4\text{H}_2\text{O} + \text{Cr}_2\text{O}_3$ State which element undergoes oxidation and which element undergoes reduction?

Electrochemistry

If lead(II) sulfide, $\text{PbS}$, is heated in air, sulfur dioxide and lead(II) oxide are produced. What is the equation for the reaction between $\text{PbS}$ and oxygen?

Atoms, molecules and stoichiometry

The diagram presents the Boltzmann distribution of energies in a gas. The gas reacts with an activation energy, $E_a$. The maximum of the distribution is marked P. If the same reaction is done in the presence of a catalyst, which statement is correct?

Reaction kinetics

Compounds X and Y react with each other to form compound Z. This reaction is reversible. $X + Y \rightleftharpoons Z$ If X and Y are put together in a closed system, a dynamic equilibrium is slowly established. Which graph could show how the rates of the forward and reverse reactions vary with time?

Equilibria

Sulfur dioxide and oxygen react reversibly. $\text{2SO}_2(g) + \text{O}_2(g) \rightleftharpoons \text{2SO}_3(g)$  $K_c = 280\,\text{mol}^{-1}\,\text{dm}^3$ at $1000\,\text{K}$ For an equilibrium mixture at $1000\,\text{K}$, the concentration of sulfur dioxide is $0.200\,\text{mol dm}^{-3}$ and that of oxygen is $0.100\,\text{mol dm}^{-3}$. Determine the concentration of sulfur trioxide.

Equilibria

Which oxide will lead to a rise in pH when it is added to water?

The Periodic Table: chemical periodicity

X, Y and Z are three elements that sit next to one another in Period 3 of the Periodic Table. Of these three, element Y has both the greatest first ionisation energy and the smallest melting point. What are the identities of X, Y and Z?

The Periodic Table: chemical periodicity

When a $5.00\,\text{g}$ portion of an anhydrous Group 2 metal nitrate is heated strongly, its mass decreases by $3.29\,\text{g}$. Which metal is present?

Atoms, molecules and stoichiometry

Solutions P and Q each have a different Group 2 ion, both at the same concentration. One solution contains $\text{Mg}^{2+}$ and the other contains $\text{Ba}^{2+}$. Separate $5\,\text{cm}^3$ samples of P and Q are tested. test 1: add $1\,\text{cm}^3$ of $0.1\,\text{mol dm}^{-3}$ $\text{Na}_2\text{SO}_4(aq)$ test 2: add $1\,\text{cm}^3$ of $0.1\,\text{mol dm}^{-3}$ $\text{NaOH}(aq)$ What outcomes are obtained in these tests?

Equilibria

Chlorine and bromine differ in volatility. Which row shows which element is more volatile, and states the correct reason?

States of matter

Sodium azide, $\text{NaN}_3$, is dissolved in water. Acidified silver nitrate is then added to the solution, producing a white precipitate. Aqueous ammonia is added next to the white precipitate. The azide ion, $\text{N}_3^-$, shows chemical properties similar to those of the $\text{Cl}^-$ ion. Which row in the table could be predicted from this information?

Group 17

What type of reaction takes place when solid ammonium sulfate is warmed with an excess of sodium hydroxide solution?

Nitrogen compounds

Catalytic converters are installed in the exhaust systems of many cars. Which gas: • leads to acid rain if it is released into the air • is taken out of car exhaust fumes by a catalytic converter?

Reaction kinetics

Diamond is a pure form of carbon. The mass of a diamond may be measured in carats. One carat is 0.200 g of carbon. Which expression shows the number of carats that contain $6.02 \times 10^{23}$ carbon atoms?

Atoms, molecules and stoichiometry

Which substance reacts with trichloroethene to form a chiral product?

Chemical bonding

Alkanes are saturated hydrocarbons. Which type of reaction do alkanes usually undergo?

Hydrocarbons

An alkene is oxidised by hot, concentrated, acidified potassium manganate(VII) to give one organic product, as illustrated. alkene $\xrightarrow{\text{hot, concentrated, acidified } \text{KMnO}_4(aq)}$ organic product What structure does the alkene have?

Hydrocarbons

A tertiary bromoalkane, represented here by $>\text{C-Br}$, undergoes reaction with aqueous NaOH. The mechanism shows the reaction pathway. Which point on the diagram has been identified correctly?

Halogen compounds

Bromoethane and chloroethane are each placed in water separately. Hydrolysis reactions take place. Which compound hydrolyses at a faster rate, and what is the mechanism?

Reaction kinetics

Alcohol X undergoes oxidation to produce compound Y. Y contains 54.54% carbon, 36.36% oxygen and 9.10% hydrogen. The $M_r$ of Y is 88.0. What might be the structure of alcohol X?

Atoms, molecules and stoichiometry

The diagram illustrates the structure of compound Z. What product is formed when compound Z reacts with an excess of NaBH$_4$?

Carbonyl compounds

Compound Q has these test results. • It forms an orange precipitate with 2,4-dinitrophenylhydrazine. • It forms a red-brown precipitate with Fehling’s reagent. • It forms a pale yellow precipitate with alkaline aqueous iodine. What is Q likely to be?

Carbonyl compounds

The compound tartaric acid, $\text{HO}_2\text{CCH(OH)CH(OH)CO}_2\text{H}$, occurs in a wide range of plants. When a sample of tartaric acid is treated with an excess of LiAlH$_4$, the organic product J is formed. What happens if NaOH(aq) is added to separate samples of tartaric acid and J?

Carboxylic acids and derivatives

If $\text{CH}_2(\text{OH})\text{CH}=\text{CHCO}_2\text{H}$ is heated gently with a small amount of concentrated sulfuric acid, a cyclic compound is produced. What is the skeletal formula of this cyclic compound?

Chemical bonding

Which molecule or ion has the smallest bond angle?

Chemical bonding

The infra-red spectrum of compound P is displayed. Which compound could P be?

Analytical techniques

One atom of germanium, Ge, has a nucleon number of $70$. Which of the following statements about a $^{{70}}_{{32}}\text{Ge}$ atom are correct?

Atomic structure

The first ionisation energy of chlorine is greater than that of sulfur. Which factors help to account for this?

The Periodic Table: chemical periodicity

Liquids $X$ and $Y$ do not react with each other, and they have the same boiling point. If a given volume of $X$ is shaken with an equal volume of $Y$, a liquid mixture $Z$ is formed. The average intermolecular forces in liquid $Z$ are stronger than the average forces in $X$ and the forces in $Y$. Which conclusions from this information are correct?

States of matter

The stoichiometry for a catalysed reaction is represented by the equation shown below. $\text{P}(g) + \text{Q}(g) \rightleftharpoons \text{R}(g) + \text{S}(l)$ Two experiments are performed, and the quantity of $R$ is measured. The outcomes are given in the diagram. Which changes in conditions might account for the results shown?

Equilibria

Which of the following statements are correct?

Atoms, molecules and stoichiometry

Nitrogen gas is unreactive, but oxygen gas and chlorine gas are reactive. Which statements explain this difference?

Chemical bonding

The structural formula of tiglic acid is $\text{CH}_3\text{CH}=\text{C}(\text{CH}_3)\text{CO}_2\text{H}$.\n\nWhich of the following statements about the properties of a single molecule of this acid are correct?

Carboxylic acids and derivatives

Which compounds, when heated with an excess of concentrated sulfuric acid, form only one product with molecular formula $\text{C}_7\text{H}_{10}$?

Hydroxy compounds

Hydrogen cyanide reacts with propanone in the presence of potassium cyanide. Which of the following statements about this reaction are correct?

Carbonyl compounds

Four compounds are displayed. $\text{C}_2\text{H}_4$\quad $\text{C}_2\text{H}_5\text{OH}$\quad $\text{CH}_3\text{CHO}$\quad $\text{CH}_3\text{CO}_2\text{H}$ What number of these compounds has an odd number of $\sigma$ bonds?

Chemical bonding

Which compounds yield three distinct organic products on hydrolysis?

Carboxylic acids and derivatives

Ethanal, $\text{CH}_3\text{CHO}$, ethanol, $\text{C}_2\text{H}_5\text{OH}$, and methoxymethane, $\text{CH}_3\text{OCH}_3$, are three organic compounds. Which of these compounds has the greatest boiling point, and which interaction makes its boiling point the greatest?

Hydroxy compounds

Determine the oxidation number of sulfur in each species? $\text{H}_2\text{S}$\quad $\text{SO}_2$\quad $\text{H}_2\text{SO}_3$

Electrochemistry

For this question, the following data will be required. $\Delta H_f^\circ(\text{N}_2\text{H}_4(l)) = 50.6\,\text{kJ mol}^{-1}$ $\Delta H_f^\circ(\text{N}_2\text{O}_4(g)) = 9.2\,\text{kJ mol}^{-1}$ $\Delta H_f^\circ(\text{H}_2\text{O}(g)) = -241.8\,\text{kJ mol}^{-1}$ Hydrazine, $\text{N}_2\text{H}_4(l)$, reacts with dinitrogen tetraoxide, $\text{N}_2\text{O}_4(g)$, to produce nitrogen gas and water vapour. $2\text{N}_2\text{H}_4(l) + \text{N}_2\text{O}_4(g) \rightarrow 3\text{N}_2(g) + 4\text{H}_2\text{O}(g)$ What is the enthalpy change for this reaction?

Chemical energetics

When sodium burns in oxygen, heat energy is released and the compound $\text{Na}_2\text{O}$ is produced. The reaction equation is shown below. $2\text{Na}(s) + \frac{1}{2}\text{O}_2(g) \rightarrow \text{Na}_2\text{O}(s)$ Which statement about this reaction is correct?

Chemical energetics

In the chemical equation, $w$, $x$, $y$ and $z$ are each whole numbers. $w\text{ClO}_3^- + x\text{MnO}_4^- + y\text{H}^+ \rightarrow w\text{ClO}_4^- + x\text{MnO}_2 + z\text{H}_2\text{O}$ After the equation has been balanced, what are the values of $w$, $x$ and $y$?

Electrochemistry