Oct/Nov 2017

Which formula gives the empirical formula of a compound?

Atoms, molecules and stoichiometry

The diagram illustrates how molecular energies are spread in a gas sample at temperature $T_1$. The activation energy for the reaction without a catalyst, $E_a\text{(uncat)}$, is shown. Which diagram correctly represents the revised distribution and the new activation energy, $E_a\text{(cat)}$, when the temperature is raised to $T_2$ and a catalyst that increases the reaction rate is added?

Reaction kinetics

$200\,\text{g}$ of water is initially at $25^{\circ}\text{C}$. The water is then heated to $75^{\circ}\text{C}$ by burning $2\,\text{g}$ of ethanol. What is the amount of energy transferred to the water?

Chemical energetics

Cl, Mg, Si and S are all elements in Period 3. Which is the correct order of their melting points, starting with the lowest and ending with the highest?

Chemical bonding

An element $Y$ undergoes the following sequence of reactions: $Y$ burns in $\text{O}_2$ and forms a white solid. This white solid reacts with $\text{HCl(aq)}$ to produce a solution. When $\text{NaOH(aq)}$ is added, a white precipitate is formed, and this precipitate dissolves in excess $\text{NaOH(aq)}$ to give a solution. Which element could $Y$ be?

The Periodic Table: chemical periodicity

Which compound would normally be applied to soil to lower its acidity?

Group 2

Dolomite is a mineral composed of a blend of magnesium carbonate and calcium carbonate. An aqueous reagent, $X$, was added to a small sample of dolomite. Bubbling was observed and a white solid, $Y$, was produced. What could be the correct identity of reagent $X$ and solid $Y$?

Group 2

Which fertiliser has the highest nitrogen percentage by mass?

Atoms, molecules and stoichiometry

When $71.0\,\text{g}$ of chlorine, $\text{Cl}_2$, are reacted with an excess of sodium hydroxide solution at a particular temperature, $35.5\,\text{g}$ of product $X$ is obtained. What is product $X$?

Atoms, molecules and stoichiometry

Compound $Q$ is a white crystalline substance that is readily soluble in water. On adding concentrated sulfuric acid to a dry sample of $Q$, steamy white fumes are produced which, when bubbled through aqueous silver nitrate solution, give a white precipitate. The precipitate dissolves in dilute ammonia solution. What is the most likely identity of compound $Q$?

Analytical techniques

The strengths of the covalent bonds inside halogen molecules, and the van der Waals’ forces acting between halogen molecules, change down Group 17 from chlorine to bromine to iodine. Which row presents these correctly?

Chemical bonding

The graph displays the relative first ionisation energies for four elements whose atomic numbers are consecutive and below 20. One of these elements reacts with hydrogen to produce a covalent compound of formula $\text{HX}$. Which element might X be?

The Periodic Table: chemical periodicity

The structural formula for compound $Q$ is given. How many stereoisomers can this structural formula have?

An introduction to AS Level organic chemistry

State the name of compound $X$?

Hydroxy compounds

A great many, though not every, organic reaction has to be heated before it takes place. Which reaction takes place rapidly at room temperature, $20^{\circ}\text{C}$?

An introduction to AS Level organic chemistry

A portion of an addition polymer chain is illustrated. $\,-\text{CH}-\text{CH}_2-\text{CH}_2-\text{CH}-\,$ with a $\text{Cl}$ group attached to each $\text{CH}$. Which monomer might have been used to produce this polymer?

Polymerisation

Which organic reaction is an instance of nucleophilic substitution?

Chemical bonding

Citric acid may be changed into tricarballylic acid in two steps. A промежmediate, $Q$, is produced. Which reagents are required for each step?

Organic synthesis

Glucose can be converted into sorbitol, a compound that is used as a sugar substitute. Which reagent could be used for this conversion?

Carbonyl compounds

$3$-methylbutanone is reacted with alkaline aqueous iodine. The resulting product mixture is then acidified. Which compound is found in the final product mixture?

Carbonyl compounds

At room temperature, propanoic acid was allowed to react to form sodium propanoate. No gas was given off in the reaction. What might the propanoic acid have reacted with?

Carboxylic acids and derivatives

Ethene is allowed to react with steam in the presence of concentrated $\text{H}_3\text{PO}_4$. The product from this reaction is then added to acidified potassium dichromate(VI) and heated under reflux for one hour. The final organic product is collected and labelled $X$. But-$2$-ene is warmed with hot, concentrated, acidified potassium manganate(VII). The final organic product is collected and labelled $Y$. Which statement is correct?

Hydroxy compounds

In which arrangement are three atoms bonded in a straight line?

Chemical bonding

A sample of the ester $\text{CH}_3\text{CH}_2\text{CH}_2\text{CO}_2\text{CH}_2\text{CH}_3$ undergoes hydrolysis. The mixture produced is then reacted with hot, acidified $\text{KMnO}_4$. What are the carbon-containing products formed at the end?

Carboxylic acids and derivatives

Many chemical terms can be defined using chemical equations. Which terms can be represented by an equation that shows a positive ion being formed?

Electrochemistry

A student prepares sodium chloride by reacting $0.025\,\text{mol}$ of sodium carbonate with excess $0.2\,\text{mol dm}^{-3}$ hydrochloric acid. $\text{Na}_2\text{CO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2$ Which of the following statements about the amounts of substance are correct?

Atoms, molecules and stoichiometry

One method for recovering tin from old printed circuit boards is to dissolve it in a mixture of concentrated hydrochloric acid and concentrated nitric acid. The tin dissolves because it reacts with the blend of these concentrated acids. $\text{Sn} + 4\text{HCl} + 2\text{HNO}_3 \rightarrow \text{SnCl}_4 + \text{NO}_2 + \text{NO} + 3\text{H}_2\text{O}$ Which statements concerning this reaction are correct?

Electrochemistry

The reaction shown below occurs in an appropriate solvent. $\text{Na}^+\text{NH}_2^- + \text{NH}_4^+\text{Cl}^- \rightarrow \text{Na}^+\text{Cl}^- + 2\text{NH}_3$ Which statements account for why this reaction should be identified as a Brønsted-Lowry acid-base reaction?

Equilibria

Which of the following statements concerning the elements barium and calcium, and their compounds, are correct?

Group 2

Which statements account for why nitrogen gas does not react easily?

Chemical bonding

Which molecules have all their carbon atoms in one plane?

Chemical bonding

A reaction pathway diagram is provided. Which reactions could produce this reaction pathway diagram?

Chemical energetics

The compounds shown below are used in perfume manufacture. Which compounds would give a yellow precipitate when treated with alkaline aqueous iodine?

Analytical techniques

In the sodium chloride lattice, the co-ordination number of the sodium ions is defined by the number of chloride ions that are nearest to each sodium ion. State the co-ordination numbers for the sodium ions and the chloride ions in the sodium chloride lattice.

Chemical bonding

The reaction in which ethanal, $\text{CH}_3\text{CHO}$, combines with $\text{HCN}$ to give $2$-hydroxypropanenitrile is catalysed by $\text{NaCN}$. What features does the intermediate in this reaction have?

Reaction kinetics

A fluorescent light tube has an internal volume of $400\,\text{cm}^3$ and an internal pressure of $200\,\text{kPa}$. It contains $0.03$ moles of an ideal gas. What is the gas temperature inside the fluorescent light tube?

States of matter

One reaction that occurs in a lead/acid cell is shown below. $\text{Pb}(s) + \text{PbO}_2(s) + 4\text{H}^+(aq) + 2\text{SO}_4^{2-}(aq) \rightarrow 2\text{PbSO}_4(s) + 2\text{H}_2\text{O}(l)$ Which statement correctly describes this reaction?

Electrochemistry

Iodine and propanone react as shown in the equation below. $\text{I}_2(aq) + \text{CH}_3\text{COCH}_3(aq) \rightarrow \text{CH}_3\text{COCH}_2\text{I}(aq) + \text{HI}(aq)$ When the concentration of propanone is raised while the total reaction volume remains constant, the reaction rate also rises. What might explain this?

Reaction kinetics

Sulfur may be oxidised in two different ways. $\text{S}(s) + \text{O}_2(g) \rightarrow \text{SO}_2(g) \quad \Delta H^\circ = -296.5\,\text{kJ mol}^{-1}$ $2\text{S}(s) + 3\text{O}_2(g) \rightarrow 2\text{SO}_3(g) \quad \Delta H^\circ = -791.4\,\text{kJ mol}^{-1}$ Sulfur trioxide may be prepared from sulfur dioxide and oxygen. $2\text{SO}_2(g) + \text{O}_2(g) \rightarrow 2\text{SO}_3(g)$ What is the standard enthalpy change for this equation?

Chemical energetics

Hydrogen iodide breaks down into hydrogen and iodine. $2\text{HI}(g) \rightleftharpoons \text{H}_2(g) + \text{I}_2(g)$ In an experiment, $b$ mol of hydrogen iodide was placed in a sealed vessel under pressure $p$. When equilibrium was reached, $x$ mol of the hydrogen iodide had dissociated. Which expression for $K_p$ is correct?

Equilibria

In which pair do the atoms have the same number of neutrons?

Atomic structure

A large excess of marble chips was allowed to react with $25\text{ cm}^3$ of $1.0\text{ mol dm}^{-3}$ hydrochloric acid at $40^\circ\text{C}$. What difference will be seen if the reaction is carried out again using $60\text{ cm}^3$ of $0.5\text{ mol dm}^{-3}$ hydrochloric acid at $40^\circ\text{C}$?

Atoms, molecules and stoichiometry

Which alteration changes the activation energy for a specified reaction?

Reaction kinetics

The relative size of property X for five elements is displayed. P, Q, R, S and T are all in Period 3 and have atomic numbers that follow one after another. Which line gives a correct match between property X and element R?

The Periodic Table: chemical periodicity

Z is an element with a giant structure. The chloride of Z reacts with water to form a solution whose pH is below 5. Which row gives two elements that could be Z?

The Periodic Table: chemical periodicity

In Group 2 of the Periodic Table, radium lies beneath barium. Which equation represents the result when solid radium nitrate, $\text{Ra(NO}_3)_2$, is heated strongly?

Group 2

A mass of exactly $3.705\text{ kg}$ of substance Y is required to neutralise $100$ moles of $\text{HCl(aq)}$. What might substance Y be?

Atoms, molecules and stoichiometry

In an experiment, $0.125$ mol of chlorine gas, $\text{Cl}_2$, is made to react with an excess of cold, aqueous sodium hydroxide. One product formed is a compound containing sodium, oxygen and chlorine. What mass of this product is formed?

Atoms, molecules and stoichiometry

Sodium bromide is reacted with concentrated sulfuric acid. What observation would be seen?

Electrochemistry

In car engines or when lightning occurs during thunderstorms, nitrogen and oxygen react to form oxides of nitrogen at high temperatures. What is the main reason that these reactions need such high temperatures?

Reaction kinetics

X is made up of a mixture containing two compounds of Group 2 elements. On heating, X undergoes thermal decomposition and yields a white solid together with only two gaseous products. One of those gases relights a glowing splint. What might the components of mixture X be?

Group 2

The formulae for two hydrocarbons are $\text{C}_W\text{H}_X$ and $\text{C}_Y\text{H}_Z$. $W$, $X$, $Y$ and $Z$ stand for different whole numbers. $\frac{W}{X} = \frac{Y}{Z}$ When the two hydrocarbons are compared, which row is correct?

Atoms, molecules and stoichiometry

Which compound does not show stereoisomerism?

An introduction to AS Level organic chemistry

The diagram illustrates the skeletal formula of citric acid. What molecular formula does citric acid have?

Atoms, molecules and stoichiometry

Which compound would give two different carboxylic acids when it is heated with concentrated, acidified manganate(VII) ions?

Hydrocarbons

In the addition polymerisation of alkenes, which bonds are broken and which bonds are formed?

Chemical bonding

When 2,3-dimethylpent-2-ene, $(\text{CH}_3)_2\text{C=C(CH}_3)\text{CH}_2\text{CH}_3$, is reacted with cold, dilute $\text{KMnO}_4$, the resulting product is then heated with an excess of concentrated $\text{H}_2\text{SO}_4$ at $180^\circ\text{C}$, producing a mixture of isomeric hydrocarbons with molecular formula $\text{C}_7\text{H}_{12}$. What is the name of one of the isomeric hydrocarbons?

Hydrocarbons

The same volume of aqueous silver nitrate was placed into separate small amounts of bromoethane and iodoethane in two test-tubes. The test-tubes were then shaken. Which row giving the observations for bromoethane is correct?

Halogen compounds

A large number, though not every one, of organic reactions have to be heated before they happen. Which reaction happens quickly at room temperature (20^{\circ}C)?

Reaction kinetics

When compound X is heated with dilute, acidified potassium dichromate(VI), no colour change occurs. X also fails to form an orange precipitate with 2,4-dinitrophenylhydrazine reagent. What might X be?

Hydroxy compounds

Which are the only structures produced when butan-2-ol is heated with concentrated $\text{H}_2\text{SO}_4$?

Hydroxy compounds

Compound G contains a chiral centre, produces a positive test with alkaline aqueous iodine, and does not form a silver mirror with Tollens’ reagent. Which compound could G be?

Hydroxy compounds

Car airbags include sodium azide, $\text{NaN}_3$, together with an excess of potassium nitrate, $\text{KNO}_3$. During a car crash, the reactions shown below take place, forming nitrogen. This makes the airbag inflate very quickly. $2\text{NaN}_3 \rightarrow 2\text{Na} + 3\text{N}_2$ $10\text{Na} + 2\text{KNO}_3 \rightarrow \text{K}_2\text{O} + 5\text{Na}_2\text{O} + \text{N}_2$ How many moles of nitrogen gas are formed in total when $1\ \text{mol}$ of sodium azide, $\text{NaN}_3$, decomposes inside an airbag?

Atoms, molecules and stoichiometry

An ester that has a banana-like smell has the formula $\text{CH}_3\text{CO}_2\text{CH}_2\text{CHCH}_2\text{CH}_3$ (with a $\text{CH}_3$ group attached to the central carbon). Which pair of reactants, when reacted under suitable conditions, would form this ester?

Organic synthesis

In 2011, an international team of scientists agreed to include two further elements in the Periodic Table. These elements were produced artificially and are named flerovium, $\text{Fl}$, and livermorium, $\text{Lv}$. Using the information in the table about atoms, which of the following statements is correct?

The Periodic Table: chemical periodicity

The chlorine oxide free radical, $\text{ClO}\cdot$, is formed when chlorine atoms react with ozone. $\text{Cl}\cdot + \text{O}_3 \rightarrow \text{ClO}\cdot + \text{O}_2$ Which characteristics are present in the chlorine oxide free radical?

Chemical bonding

Hydrogen sulfide may be oxidised to produce sulfur dioxide. $2\text{H}_2\text{S} + 3\text{O}_2 \rightarrow 2\text{SO}_2 + 2\text{H}_2\text{O}$ Which of these statements are correct?

Electrochemistry

Methanoic acid, $\text{HCO}_2\text{H}$, and hydrocyanic acid, $\text{HCN}$, are both able to act as acids. A solution of methanoic acid has a smaller pH than a hydrocyanic acid solution with the same concentration. Which statements account for this?

Equilibria

Which statements accurately describe a trend when moving down Group 2?

Group 2

Modern cars are equipped with catalytic converters to cut air pollution produced by undesirable reactions that take place during fuel combustion. Which statements are correct?

Reaction kinetics

Which of the following statements are correct for an $\mathrm{S_N2}$ mechanism?

Reaction kinetics

Bromoethane is heated under reflux with concentrated aqueous $\mathrm{NaOH}$. Which of the following statements are correct?

Halogen compounds

Compound M is an important component of perfume. M reacts with $\mathrm{HCN}$. Which statements about this reaction are correct?

Carbonyl compounds

When ethane burns in oxygen, carbon dioxide and water vapour are produced. What bond angles are found in the molecules of ethane and in the products of its combustion?

Chemical bonding

Carboxylic acids may be changed into their salts through several reactions at room temperature. Which reaction would form sodium butanoate and a gas?

Carboxylic acids and derivatives

A sample of ideal gas is kept in a gas syringe at a fixed temperature of $300\ \text{K}$. Its pressure is raised, and a graph of $\frac{pV}{RT}$ against pressure is drawn. Which graph correctly shows the results?

States of matter

To calculate the enthalpy change, $\Delta H$, for an experiment that uses solutions, the mass of the solution, $m$, the specific heat capacity of the solution, $c$, and the temperature change, $\Delta T$, are required. $\Delta T = T_{\text{final}} - T_{\text{initial}}$ Which expression for $\Delta H$ is correct?

Chemical energetics

Use the information below to answer this question. $\Delta H_f^\circ(\text{P}_4\text{O}_{10}(s)) = -3012\ \text{kJ mol}^{-1}$ $\Delta H_f^\circ(\text{H}_2\text{O}(l)) = -286\ \text{kJ mol}^{-1}$ $\Delta H_f^\circ(\text{H}_3\text{PO}_4(s)) = -1279\ \text{kJ mol}^{-1}$ What is $\Delta H^\circ$ for the reaction displayed? $\text{P}_4\text{O}_{10}(s) + 6\text{H}_2\text{O}(l) \rightarrow 4\text{H}_3\text{PO}_4(s)$

Chemical energetics

Which statement is always true for an oxidation reaction?

Electrochemistry

Nitrogen dioxide, $\text{NO}_2$, is a brown gas. Dinitrogen tetroxide, $\text{N}_2\text{O}_4$, is a colourless gas. In a closed vessel, an equilibrium is set up between $\text{NO}_2$ and $\text{N}_2\text{O}_4$. $2\text{NO}_2(g) \rightleftharpoons \text{N}_2\text{O}_4(g) \qquad \Delta H = -57\ \text{kJ mol}^{-1}$ Which row gives the effect of altering the conditions on the colour of an equilibrium mixture of $\text{NO}_2$ and $\text{N}_2\text{O}_4$?

Equilibria

Which formula shows the empirical formula of a compound?

Atoms, molecules and stoichiometry

The diagram illustrates how the molecular energies are distributed in a gas sample at temperature $T_1$. The activation energy for the gas’s uncatalysed reaction, $E_a(\text{uncat})$, is indicated. Which diagram most accurately displays the revised distribution and the revised activation energy, $E_a(\text{cat})$, after the temperature is raised to $T_2$, and a catalyst is added to increase the reaction rate?

Reaction kinetics

A sample of 200 g of water is initially at $25\degree\text{C}$. It is then warmed to $75\degree\text{C}$ by burning 2 g of ethanol. What is the amount of energy transferred to the water?

Chemical energetics

The elements Cl, Mg, Si and S are all located in Period 3. Which of these has the correct order of melting points, arranged from the lowest to the highest?

The Periodic Table: chemical periodicity

Element Y undergoes the following reaction pathway: $Y$ is burned in $\text{O}_2 \rightarrow$ white solid $\xrightarrow{\text{HCl(aq)}}$ solution $\xrightarrow{\text{NaOH(aq)}}$ white precipitate $\xrightarrow{\text{excess NaOH(aq)}}$ solution. What might element Y be?

The Periodic Table: chemical periodicity

Which compound would most commonly be added to soil to decrease its acidity?

Equilibria

The mineral dolomite is made up of magnesium carbonate and calcium carbonate. An aqueous reagent, X, was added to a small sample of dolomite. Effervescence was observed and a white solid, Y, was produced. What might be the correct identity of reagent X and solid Y?

Group 2

Which fertiliser has the highest percentage of nitrogen by mass?

Atoms, molecules and stoichiometry

At a chosen temperature, 71.0 g of chlorine, $\text{Cl}_2$, is allowed to react with an excess amount of sodium hydroxide solution. Exactly 35.5 g of product X is formed. What is product X?

Group 17

Compound Q is a white crystalline solid that dissolves readily in water. If concentrated sulfuric acid is added to a dry sample of Q, steamy white fumes are produced; when these are passed into aqueous silver nitrate solution, a white precipitate is formed. This precipitate dissolves in dilute ammonia solution. What could be the identity of compound Q?

Group 17

The bond strengths of the covalent bonds inside halogen molecules, together with the van der Waals’ forces between halogen molecules, change down Group 17 from chlorine to bromine to iodine. Which row shows these correctly?

Chemical bonding

The graph displays the relative first ionisation energies for four elements whose atomic numbers are consecutive and less than 20. One of these elements reacts with hydrogen to make a covalent compound with the formula $\text{HX}$. Which element could X be?

The Periodic Table: chemical periodicity

The structural formula of compound Q is shown. With this structural formula, how many stereoisomers are there?

Chemical bonding

What is compound X called?

Hydroxy compounds

A number of organic reactions, though not every one, have to be warmed before they will take place. Which reaction takes place rapidly at room temperature, $20\degree\text{C}$?

Reaction kinetics

A portion of an addition polymer chain is displayed. Which monomer could have been used to form this polymer?

Polymerisation

Which organic reaction counts as an example of nucleophilic substitution?

An introduction to AS Level organic chemistry

Citric acid may be changed into tricarballylic acid in two steps. A compound intermediate, Q, is produced. Which reagents are required for each step?

Organic synthesis

Glucose can be converted into sorbitol, a compound that is used as a sugar substitute. Which reagent could be used for this conversion?

Carbonyl compounds

3-methylbutanone is reacted with alkaline aqueous iodine. The resulting product mixture is then acidified. Which compound is found in the final product mixture?

Carbonyl compounds

At room temperature, propanoic acid was allowed to react so that sodium propanoate was formed. No gas was given off in the reaction. What could the propanoic acid have reacted with?

Carboxylic acids and derivatives

Steam is added to ethene in the presence of concentrated $\text{H}_3\text{PO}_4$. The product from this reaction is then mixed with acidified potassium dichromate(VI) and heated under reflux for one hour. The final organic product is isolated and given the label X. But-2-ene is then treated with hot, concentrated, acidified potassium manganate(VII). The final organic product is isolated and given the label Y. Which statement is correct?

Hydroxy compounds

In what type of structure are three atoms joined in a straight line?

Chemical bonding

When a sample of the ester $\text{CH}_3\text{CH}_2\text{CH}_2\text{CO}_2\text{CH}_2\text{CH}_3$ is hydrolysed, the mixture formed is then treated with hot, acidified $\text{KMnO}_4$. Which carbon-containing products are present at the end?

Carboxylic acids and derivatives

Many chemical terms can be shown using chemical equations. Which term can be represented by an equation that shows the formation of a positive ion?

Chemical bonding

A student prepares sodium chloride by letting $0.025$ mol of sodium carbonate react with an excess of $0.2\,\text{mol dm}^{-3}$ hydrochloric acid. $\text{Na}_2\text{CO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2$. Which statements concerning the amounts of substance are correct?

Atoms, molecules and stoichiometry

One method for recovering tin from obsolete printed circuit boards is to dissolve it in a combination of concentrated hydrochloric acid and concentrated nitric acid. The tin dissolves because it reacts with this mixture of concentrated acids. $\text{Sn} + 4\text{HCl} + 2\text{HNO}_3 \rightarrow \text{SnCl}_4 + \text{NO}_2 + \text{NO} + 3\text{H}_2\text{O}$ Which of the following statements about this reaction are correct?

Electrochemistry

The reaction shown below occurs in a suitable solvent. $\text{Na}^+\text{NH}_2^- + \text{NH}_4^+\text{Cl}^- \rightarrow \text{Na}^+\text{Cl}^- + 2\text{NH}_3$ Which statements justify classifying this reaction as a Brønsted-Lowry acid-base reaction?

Equilibria

Which of these statements about the elements barium and calcium and their compounds are correct?

Group 2

Which statements account for nitrogen gas being unreactive?

Nitrogen and sulfur

Which molecules have every carbon atom in one plane?

Chemical bonding

A reaction pathway diagram is shown. Which reactions could be represented by this reaction pathway diagram?

Chemical energetics

The compounds shown below are used in the production of perfumes. Which compounds would give a yellow precipitate with alkaline aqueous iodine?

Carbonyl compounds

In the sodium chloride lattice, the number of chloride ions surrounding each sodium ion is known as the co-ordination number of the sodium ions. What are the co-ordination numbers of the sodium ions and the chloride ions in the sodium chloride lattice?

Chemical bonding

When ethanal, $\text{CH}_3\text{CHO}$, reacts with HCN to give 2-hydroxypropanenitrile, NaCN acts as the catalyst. What characteristics does the intermediate in this reaction have?

Reaction kinetics

A fluorescent lamp tube has an internal volume of $400\text{ cm}^3$ and an internal pressure of $200\text{ kPa}$. It contains $0.03$ moles of an ideal gas. What is the gas temperature inside the fluorescent lamp tube?

States of matter

A reaction occurring in a lead/acid cell is given below. $\text{Pb}(s) + \text{PbO}_2(s) + 4\text{H}^+(aq) + 2\text{SO}_4^{2-}(aq) \rightarrow 2\text{PbSO}_4(s) + 2\text{H}_2\text{O}(l)$ Which statement correctly describes this reaction?

Electrochemistry

Iodine and propanone react in accordance with the equation below. $\text{I}_2(aq) + \text{CH}_3\text{COCH}_3(aq) \rightarrow \text{CH}_3\text{COCH}_2\text{I}(aq) + \text{HI}(aq)$ When the concentration of propanone is raised, while the total reaction volume remains unchanged, the reaction rate also rises. What might explain this?

Reaction kinetics

There are two possible oxidation routes for sulfur. $\text{S}(s) + \text{O}_2(g) \rightarrow \text{SO}_2(g) \quad \Delta H^\circ = -296.5\,\text{kJ mol}^{-1}$ $2\text{S}(s) + 3\text{O}_2(g) \rightarrow 2\text{SO}_3(g) \quad \Delta H^\circ = -791.4\,\text{kJ mol}^{-1}$ Sulfur trioxide is formed when sulfur dioxide reacts with oxygen. $2\text{SO}_2(g) + \text{O}_2(g) \rightarrow 2\text{SO}_3(g)$ Calculate the standard enthalpy change, $\Delta H^\circ$, for this reaction.

Chemical energetics

Hydrogen iodide breaks down into hydrogen and iodine. $2\text{HI}(g) \rightleftharpoons \text{H}_2(g) + \text{I}_2(g)$ For an experiment, $b$ mol of hydrogen iodide was introduced into a sealed container at pressure $p$. When equilibrium was reached, $x$ mol of the hydrogen iodide had dissociated. Which expression for $K_p$ is correct?

Equilibria