Chemical energetics

Which equation shows a reaction enthalpy that is equal to the standard enthalpy change of atomisation of chlorine?

Feb/March 2016

The diagram shows the enthalpy changes for a series of reactions. R $\rightarrow$ S with $\Delta H = -134\ \text{kJ mol}^{-1}$ S $\rightarrow$ U with $\Delta H = +92\ \text{kJ mol}^{-1}$ R $\rightarrow$ T with $\Delta H = -75\ \text{kJ mol}^{-1}$ T $\rightarrow$ U Which of the following statements are correct?

Feb/March 2016

Nitric oxide, $\text{NO}$, and bromine vapour react with each other according to the equation below. $2\text{NO(g)} + \text{Br}_2\text{(g)} \rightarrow 2\text{NOBr(g)} \qquad \Delta H^\circ = -23\ \text{kJ mol}^{-1}$ For this reaction, the activation energy is $+5.4\ \text{kJ mol}^{-1}$. Which reaction pathway diagram is correct for this reaction?

Feb/March 2016

A student combined $25.0\,\text{cm}^3$ of $4.00\,\text{mol dm}^{-3}$ hydrochloric acid with the same volume of $4.00\,\text{mol dm}^{-3}$ sodium hydroxide. At the start, both solutions were at $15.0\,^{\circ}\text{C}$. The greatest temperature measured was $30.0\,^{\circ}\text{C}$. From these measurements, determine the enthalpy change of neutralisation of hydrochloric acid?

Feb/March 2017

Which equation shows the standard enthalpy change of formation of water?

Feb/March 2018

Hess’ Law together with bond energy data may be used to work out the enthalpy change of a reaction. Bromoethane, $\text{CH}_3\text{CH}_2\text{Br}$, can be prepared by reacting ethene with hydrogen bromide. $\text{CH}_2{=}\text{CH}_2 + \text{HBr} \rightarrow \text{CH}_3\text{CH}_2\text{Br}$. What is the enthalpy change for this reaction?

Feb/March 2018

At standard conditions, which statement is correct?

Feb/March 2019

The standard enthalpy changes for combustion of carbon, hydrogen and methanol are listed below. $\text{C}(s)+\text{O}_2(g)\rightarrow\text{CO}_2(g)\quad\Delta H_c^\circ=-394\,\text{kJ mol}^{-1}$ $\text{H}_2(g)+\frac{1}{2}\text{O}_2(g)\rightarrow\text{H}_2\text{O}(l)\quad\Delta H_c^\circ=-286\,\text{kJ mol}^{-1}$ $\text{CH}_3\text{OH}(l)+\frac{3}{2}\text{O}_2(g)\rightarrow\text{CO}_2(g)+2\text{H}_2\text{O}(l)\quad\Delta H_c^\circ=-726\,\text{kJ mol}^{-1}$ Which expression represents the standard enthalpy change of formation of methanol, in $\text{kJ mol}^{-1}$?

Feb/March 2019

A chemical reaction equation is given below. Every substance is in its standard state. $\text{XeF}_6 + 3\text{H}_2\text{O} \rightarrow \text{XeO}_3 + 6\text{HF}$ Which statement gives the standard enthalpy change of reaction for this reaction?

Feb/March 2019

A reaction involving carbon and oxygen is given. $\text{C(s)} + \frac{1}{2}\text{O}_2\text{(g)} \rightarrow \text{CO(g)}$ Which description correctly identifies the standard enthalpy change for this reaction?

Feb/March 2020

Use the information below to answer this question. $\text{NaHCO}_3(s) + \text{HCl}(aq) \rightarrow \text{NaCl}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$, $\Delta H = -38.97\ \text{kJ mol}^{-1}$ $\text{Na}_2\text{CO}_3(s) + 2\text{HCl}(aq) \rightarrow 2\text{NaCl}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$, $\Delta H = -96.59\ \text{kJ mol}^{-1}$ When heated, sodium hydrogencarbonate breaks down as follows. $2\text{NaHCO}_3(s) \rightarrow \text{Na}_2\text{CO}_3(s) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$ Determine the enthalpy change for this decomposition?

Feb/March 2020

The energy cycle for the combustion of methane is illustrated here. $\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(l)$ Which of these expressions may be used to work out the energy change, $\Delta H_z$?

Feb/March 2021

An experiment was carried out to find the enthalpy of combustion of ethanol. The recorded data are: mass of water $= W\,\text{g}$; mass of ethanol burned $= X\,\text{g}$; temperature rise $= Y^{\circ}\text{C}$; molar mass of ethanol $= Z\,\text{g mol}^{-1}$; specific heat capacity of water $= 4.2\,\text{J K}^{-1}\text{g}^{-1}$. Which expression may be used to work out the enthalpy of combustion of ethanol in $\text{kJ mol}^{-1}$?

Feb/March 2021

Reaction 1 is represented by the equation shown here. Reaction 1: $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 \rightarrow 2\mathrm{CO}_2 + 2\mathrm{C}_2\mathrm{H}_5\mathrm{OH}$. The standard enthalpy changes of combustion, $\Delta H_c^\circ$, are: for $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$ it is $a$, and for $\mathrm{C}_2\mathrm{H}_5\mathrm{OH}$ it is $b$, in $\text{kJ mol}^{-1}$. Which expression gives the enthalpy change of reaction 1 correctly?

Feb/March 2022

Nitrogen monoxide is an atmospheric pollutant produced in car engines by an endothermic reaction of nitrogen with oxygen. $\text{N}_2(g) + \text{O}_2(g) \rightarrow 2\text{NO}(g)$ Which diagram shows the energy profile that corresponds to this reaction?

Feb/March 2022

The chemical equation for a reaction is given below. Every substance is in its standard state. $\text{XeF}_6 + 3\text{H}_2\text{O} \rightarrow \text{XeO}_3 + 6\text{HF}$ Which statement gives the standard enthalpy change of reaction for this reaction?

Feb/March 2023

Which reaction corresponds to the standard enthalpy change of formation of propane?

Feb/March 2024

Which process has the greatest enthalpy change per mole?

Feb/March 2024

For the reaction below, the enthalpy change is given as $\Delta H_r^\circ$. $2\text{C}_2\text{H}_6(g) + 3\text{O}_2(g) \rightarrow 2\text{CH}_4(g) + 2\text{CO}_2(g) + 2\text{H}_2\text{O}(l)$. Which expression could be used to determine $\Delta H_r^$?

Feb/March 2024

A student combines $25.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ sodium hydroxide solution with $25.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ hydrochloric acid, and the student measures a temperature increase of $2.50\,^{\circ}\text{C}$. What is the enthalpy change of the reaction per mole of NaOH?

Feb/March 2025

Carbon monoxide and methanol may react together to produce ethanoic acid. $\text{CO}(g) + \text{CH}_3\text{OH}(l) \xrightarrow[]{\Delta H^{\circ}} \text{CH}_3\text{CO}_2\text{H}(l)$ The table lists the standard enthalpy changes of combustion. $\Delta H_c^{\circ}(\text{CO}) = -283.0\,\text{kJ mol}^{-1}$ $\Delta H_c^{\circ}(\text{CH}_3\text{OH}) = -726.0\,\text{kJ mol}^{-1}$ $\Delta H_c^{\circ}(\text{CH}_3\text{CO}_2\text{H}) = -874.1\,\text{kJ mol}^{-1}$ Determine the value of $\Delta H_r^{\circ}$ for the reaction between carbon monoxide and methanol?

Feb/March 2025

Every reactant and product in an exothermic reaction is in the gaseous state. Which statement about this reaction is correct?

Feb/March 2025

The bond energy data below are given. C-H: $410\ \text{kJ mol}^{-1}$ C-Cl: $340\ \text{kJ mol}^{-1}$ Cl-Cl: $244\ \text{kJ mol}^{-1}$ Br-Br: $193\ \text{kJ mol}^{-1}$ These bond energy data correspond to the four reactions shown here. P: $\text{Br}_2 \rightarrow 2\text{Br}$ Q: $2\text{Cl} \rightarrow \text{Cl}_2$ R: $\text{CH}_3 + \text{Cl} \rightarrow \text{CH}_3\text{Cl}$ S: $\text{CH}_4 \rightarrow \text{CH}_3 + \text{H}$ Which sequence correctly arranges the enthalpy changes for these reactions from the most negative to the most positive?

May/June 2010

Using the enthalpy changes shown below, $\text{I}_2(g) + 3\text{Cl}_2(g) \rightarrow 2\text{ICl}_3(s) \quad \Delta H^\circ = -214\ \text{kJ mol}^{-1}$ $\text{I}_2(s) \rightarrow \text{I}_2(g) \quad \Delta H^\circ = +38\ \text{kJ mol}^{-1}$ What is the standard enthalpy change of formation of iodine trichloride, $\text{ICl}_3(s)$?

May/June 2010

The bond energy data shown are listed here. Bond energies: C-H: $410\ \text{kJ mol}^{-1}$ C-Cl: $340\ \text{kJ mol}^{-1}$ Cl-Cl: $244\ \text{kJ mol}^{-1}$ Br-Br: $193\ \text{kJ mol}^{-1}$ These bond energy values correspond to the four reactions below: P: $\text{Br}_2 \rightarrow 2\text{Br}$ Q: $2\text{Cl} \rightarrow \text{Cl}_2$ R: $\text{CH}_3 + \text{Cl} \rightarrow \text{CH}_3\text{Cl}$ S: $\text{CH}_4 \rightarrow \text{CH}_3 + \text{H}$ In which sequence do the enthalpy changes of these reactions run from the most negative to the most positive?

May/June 2010

Using the enthalpy changes shown below, $I_2(g) + 3\text{Cl}_2(g) \rightarrow 2\text{ICl}_3(s)$ $\Delta H^\circ = -214\ \text{kJ mol}^{-1}$ $I_2(s) \rightarrow I_2(g)$ $\Delta H^\circ = +38\ \text{kJ mol}^{-1}$ Calculate the standard enthalpy change of formation for iodine trichloride, $\text{ICl}_3(s)$?

May/June 2010

Using the enthalpy changes below, $\text{I}_2(g) + 3\text{Cl}_2(g) \rightarrow 2\text{ICl}_3(s)$, $\Delta H^\circ = -214\,\text{kJ mol}^{-1}$ $\text{I}_2(s) \rightarrow \text{I}_2(g)$, $\Delta H^\circ = +38\,\text{kJ mol}^{-1}$ What is the standard enthalpy change of formation of iodine trichloride, $\text{ICl}_3(s)$?

May/June 2010

Several bond energy values are given below. These bond energy values are connected to the following four reactions: $\text{P: } \text{Br}_2 \rightarrow 2\text{Br}$ $\text{Q: } 2\text{Cl} \rightarrow \text{Cl}_2$ $\text{R: } \text{CH}_3 + \text{Cl} \rightarrow \text{CH}_3\text{Cl}$ $\text{S: } \text{CH}_4 \rightarrow \text{CH}_3 + \text{H}$ In what sequence should the enthalpy changes for these reactions be arranged, from the most negative to the most positive?

May/June 2010

The equation given here shows gaseous atoms of non-metal X and hydrogen combining to produce gaseous $\text{X}_2\text{H}_6$ molecules. $2\text{X(g)} + 6\text{H(g)} \rightarrow \text{X}_2\text{H}_6\text{(g)} \qquad \Delta H = -2775\,\text{kJ mol}^{-1}$ The bond energy for an X-H bond is $395\,\text{kJ mol}^{-1}$. Calculate the bond energy of an X-X bond.

May/June 2011

50 cm$^3$ of 2.50 mol dm$^{-3}$ hydrochloric acid was put into a polystyrene beaker with negligible heat capacity. The temperature was measured and then 50 cm$^3$ of 2.50 mol dm$^{-3}$ NaOH, initially at the same temperature, was rapidly added while stirring. The temperature increased by 17 ^{\circ}C. The final solution can be taken to have a specific heat capacity of 4.2 J g$^{-1}$ K$^{-1}$. What is an approximate value for the molar enthalpy change of neutralisation of hydrochloric acid and sodium hydroxide from this experiment?

May/June 2011

Titanium is found in nature as the mineral rutile, $\text{TiO}_2$. One way to extract titanium is to heat the rutile with carbon so that reduction occurs. $\text{TiO}_2(s) + 2\text{C}(s) \rightarrow \text{Ti}(s) + 2\text{CO}(g)$ The standard enthalpy changes of formation of $\text{TiO}_2(s)$ and $\text{CO}(g)$ are $-940\,\text{kJ mol}^{-1}$ and $-110\,\text{kJ mol}^{-1}$ respectively. Determine the standard enthalpy change for this reaction.

May/June 2011

Which reaction has an enthalpy change that is the same as the standard enthalpy change of formation of propane?

May/June 2011

When compound X was changed into compound Z, the reaction was observed to pass through compound Y, and Y could be isolated. The sequence of stages was as follows. $X \rightarrow Y ; \Delta H$ positive $Y \rightarrow Z ; \Delta H$ negative Which reaction profile is consistent with these results?

May/June 2011

$50\ \text{cm}^3$ of $2.50\ \text{mol dm}^{-3}$ hydrochloric acid was poured into a polystyrene beaker with negligible heat capacity. Its temperature was measured, after which $50\ \text{cm}^3$ of $2.50\ \text{mol dm}^{-3}$ NaOH at the same temperature was added rapidly, with stirring. The temperature increased by $17\ ^\circ\text{C}$. For the purposes of the calculation, the final solution can be treated as having a specific heat capacity of $4.2\ \text{J g}^{-1}\ \text{K}^{-1}$. What approximate value would you obtain for the molar enthalpy change of neutralisation of hydrochloric acid and sodium hydroxide from this experiment?

May/June 2011

The equation shown describes gaseous atoms of non-metal X and hydrogen combining to produce gaseous $\text{X}_2\text{H}_6$ molecules. $2\text{X}(g) + 6\text{H}(g) \rightarrow \text{X}_2\text{H}_6(g) \quad \Delta H = -2775\,\text{kJ mol}^{-1}$ The bond energy for an X-H bond is $395\,\text{kJ mol}^{-1}$. Determine the bond energy of an X-X bond?

May/June 2011

A reaction pathway diagram is shown. Which reaction is not represented by this profile?

May/June 2012

The equation for a reaction is given below. $\text{H}_2(\text{g}) + \frac{1}{2}\text{O}_2(\text{g}) \rightarrow \text{H}_2\text{O}(\ell)\ ; \Delta H = x\ \text{kJ mol}^{-1}$ Which pair of statements is entirely correct for this reaction?

May/June 2012

Propanone has the molecular formula $\text{C}_3\text{H}_6\text{O}$. The enthalpy change of combustion of hydrogen is $-286\ \text{kJ mol}^{-1}$. The enthalpy change of combustion of carbon is $-394\ \text{kJ mol}^{-1}$. The enthalpy change of combustion of propanone is $-1786\ \text{kJ mol}^{-1}$. From this data, determine the enthalpy change of formation of propanone?

May/June 2012

Red lead oxide, $\text{Pb}_3\text{O}_4$, is used in metal priming paints. It can be prepared by heating PbO in air. $6\text{PbO(s)} + \text{O}_2\text{(g)} \rightarrow 2\text{Pb}_3\text{O}_4\text{(s)}$. Which two quantities are required to calculate the enthalpy change for this reaction?

May/June 2012

Slaked lime, $\text{Ca(OH)}_2$, can be produced starting from limestone, $\text{CaCO}_3$. When limestone is heated in a lime kiln at $1000^\circ\text{C}$, it breaks down according to the equation below. reaction 1: $\text{CaCO}_3(s) \rightarrow \text{CaO}(s) + \text{CO}_2(g)$ Water is then added to calcium oxide, $\text{CaO}$, in the reaction shown below. reaction 2: $\text{CaO}(s) + \text{H}_2\text{O}(l) \rightarrow \text{Ca(OH)}_2(s)$ What are the enthalpy changes of these reactions?

May/June 2012

A reaction pathway diagram is shown. Which reaction does not show this kind of profile?

May/June 2012

A reaction equation is given below. $\text{H}_2(g) + \tfrac{1}{2}\text{O}_2(g) \rightarrow \text{H}_2\text{O}(l) ;\ \Delta H = x\,\text{kJ mol}^{-1}$ Which pair of statements is entirely correct for this reaction?

May/June 2012

The molecular formula of propanone is $\text{C}_3\text{H}_6\text{O}$. The enthalpy change of combustion of hydrogen is $-286\,\text{kJ mol}^{-1}$. The enthalpy change of combustion of carbon is $-394\,\text{kJ mol}^{-1}$. The enthalpy change of combustion of propanone is $-1786\,\text{kJ mol}^{-1}$. From this data, determine the enthalpy change of formation of propanone.

May/June 2012

Bond enthalpy data should be used to answer this question. The equation below shows the complete combustion of methane. $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$ What is the enthalpy change of combustion of methane?

May/June 2013

The reaction pathway for a reversible reaction is displayed below. Which statement is right?

May/June 2013

This question requires use of the Data Booklet. A student combined $25\ \text{cm}^3$ of $0.10\ \text{mol dm}^{-3}$ sodium hydroxide solution with $25\ \text{cm}^3$ of $0.10\ \text{mol dm}^{-3}$ hydrochloric acid and observed a temperature increase of $2.5^\circ\text{C}$. Determine the enthalpy change for the reaction per mole of NaOH.

May/June 2013

What energy change is represented by the enthalpy change of atomisation of hydrogen at $298\ \text{K}$?

May/June 2013

Propanone has the molecular formula $\text{C}_3\text{H}_6\text{O}$. The enthalpy change of combustion of hydrogen is $-286\ \text{kJ mol}^{-1}$. The enthalpy change of combustion of carbon is $-394\ \text{kJ mol}^{-1}$. The enthalpy change of formation of propanone is $-254\ \text{kJ mol}^{-1}$. Using this data, what is the enthalpy change of combustion of propanone?

May/June 2013

Four equations for enthalpy changes are given below. $\text{Na(g)} \rightarrow \text{Na}^+(g) + e^- \quad \Delta H = W$ $\text{Na(g)} \rightarrow \text{Na}^{2+}(g) + 2e^- \quad \Delta H = X$ $\text{Na(s)} \rightarrow \text{Na(g)} \quad \Delta H = Y$ $\text{Na(s)} \rightarrow \text{Na}^{2+}(g) + 2e^- \quad \Delta H = Z$ Determine the second ionisation energy of sodium.

May/June 2013

The diagram illustrates the reaction pathway of a reversible reaction. Which statements are correct?

May/June 2013

This question requires use of the Data Booklet. Answer this question using bond enthalpy data. The equation below shows the complete combustion of methanal. $ \text{H}_2\text{C}=\text{O} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} $ What is the enthalpy change of combustion for methanal?

May/June 2013

The pathway diagram for a reversible reaction is shown below. Which of the statements are correct?

May/June 2013

The thermal decomposition of Group II nitrates follows the equation below. $\text{X(NO}_3)_2 \rightarrow \text{XO} + 2\text{NO}_2 + \tfrac{1}{2}\text{O}_2$ Which Group II nitrate needs the greatest temperature for its thermal decomposition to occur?

May/June 2014

Enthalpy changes that are not easy to measure directly can often be found by using Hess’ Law to build an enthalpy cycle. Which enthalpy change does X represent in the enthalpy cycle shown? The cycle shows $\text{C(s)} + 2\text{H}_2\text{(g)} + 2\text{O}_2\text{(g)}$ changing to $\text{CH}_4\text{(g)} + 2\text{O}_2\text{(g)}$ with $\Delta H_f^\circ$, then to $\text{CO}_2\text{(g)} + 2\text{H}_2\text{O(l)}$ with $\Delta H_f^\circ$, and reaction arrows labelled $\Delta H_c^\circ$ and X.

May/June 2014

A student combined $25.0\,\text{cm}^3$ of $0.350\,\text{mol dm}^{-3}$ sodium hydroxide solution with $25.0\,\text{cm}^3$ of $0.350\,\text{mol dm}^{-3}$ hydrochloric acid. The temperature increased by $2.50\,^\circ\text{C}$. Assume that none of the heat was transferred to the surroundings. The resulting mixture had a specific heat capacity of $4.20\,\text{J cm}^{-3}\,\text{K}^{-1}$. Calculate the molar enthalpy change for the reaction.

May/June 2014

The diagram illustrates the skeletal formula of cyclopropane. The enthalpy change of formation of cyclopropane is $+53.3\,\text{kJ mol}^{-1}$, while the enthalpy change of atomisation of graphite is $+717\,\text{kJ mol}^{-1}$. The bond enthalpy of H-H is $436\,\text{kJ mol}^{-1}$ and that of C-H is $410\,\text{kJ mol}^{-1}$. What value for the mean bond enthalpy of the C-C bond in cyclopropane can be determined from these data?

May/June 2014

For carbon dioxide, the enthalpy change of formation is $-394\,\text{kJ mol}^{-1}$, for water it is $-286\,\text{kJ mol}^{-1}$, and for methane it is $-74\,\text{kJ mol}^{-1}$. Calculate the enthalpy change of combustion of methane.

May/June 2014

Which equation shows the standard enthalpy change of formation of ethanol, $\text{C}_2\text{H}_5\text{OH}$?

May/June 2014

Which reaction corresponds to the standard enthalpy change of formation of propane?

May/June 2014

A student carries out an investigation using four different fuels. The fuels are tested one at a time to increase the temperature of $1\ \text{dm}^3$ of water from $20\degree\text{C}$ to $100\degree\text{C}$. In every case, the fuel burns completely. All the other conditions remain unchanged for each experiment. Which fuel would give the smallest amount of carbon dioxide in these experiments?

May/June 2014

A reaction pathway diagram is given. For which enthalpy change would this diagram not be suitable?

May/June 2014

The enthalpy change of formation of $\text{Mn(NO}_3)_2(s)$ is $-696\,\text{kJ mol}^{-1}$. The enthalpy change of formation of $\text{MnO}_2(s)$ is $-520\,\text{kJ mol}^{-1}$. The enthalpy change of formation of $\text{NO}_2(g)$ is $+33\,\text{kJ mol}^{-1}$. When heated, $\text{Mn(NO}_3)_2$ breaks down to form $\text{MnO}_2$ and $\text{NO}_2$. $\text{Mn(NO}_3)_2(s) \rightarrow \text{MnO}_2(s) + 2\text{NO}_2(g)$. What is the standard enthalpy change for this reaction?

May/June 2014

The standard enthalpy changes of combustion for glucose and ethanol are $-2820$ and $-1368\,\text{kJ mol}^{-1}$, respectively. Glucose, $\text{C}_6\text{H}_{12}\text{O}_6$, can be changed into ethanol. $\text{C}_6\text{H}_{12}\text{O}_6(s) \rightarrow 2\text{C}_2\text{H}_5\text{OH}(l) + 2\text{CO}_2(g)$ Calculate the standard enthalpy change for this reaction?

May/June 2015

Which statements are true for every exothermic reaction?

May/June 2015

Metaldehyde, $(\text{CH}_3\text{CHO})_4$, is employed as a solid fuel in camping stoves. The equation for metaldehyde’s complete combustion is given below. $(\text{CH}_3\text{CHO})_4(s) + 10\text{O}_2(g) \rightarrow 8\text{CO}_2(g) + 8\text{H}_2\text{O}(l)$ $\Delta H_c^{\circ}$ = standard enthalpy change of combustion. Which expression gives the correct value for the enthalpy change of formation of metaldehyde?

May/June 2015

In an experiment, a student set out to determine the enthalpy change of combustion of ethane. He took the following values for the standard enthalpy changes of combustion of carbon and hydrogen. $\Delta H_c^{\circ}(\text{carbon}) = -394\,\text{kJ mol}^{-1}$ $\Delta H_c^{\circ}(\text{hydrogen}) = -286\,\text{kJ mol}^{-1}$ From his calculations, the enthalpy change of formation of ethane was found to be $-140\,\text{kJ mol}^{-1}$. What experimental value did he obtain for the standard enthalpy change of combustion of ethane?

May/June 2015

Carbon monoxide and methanol can combine to produce ethanoic acid. $\text{CO(g)} + \text{CH}_3\text{OH(l)} \xrightarrow{\Delta H_r^{\circ}} \text{CH}_3\text{CO}_2\text{H(l)}$ The table provides standard enthalpy changes of combustion. What value is obtained for $\Delta H_r^{\circ}$ for the reaction between carbon monoxide and methanol?

May/June 2015

Which equation represents the reaction occurring in the standard enthalpy change of atomisation of bromine?

May/June 2016

When gaseous phosphorus pentachloride is heated, it breaks down to form gaseous phosphorus trichloride and chlorine. The table lists the bond energies. Bond energies: $\text{P-Cl}$ (in both chlorides): $330\,\text{kJ mol}^{-1}$ $\text{Cl-Cl}$: $242\,\text{kJ mol}^{-1}$ What is the enthalpy change for the decomposition of $\text{PCl}_5$ into $\text{PCl}_3$ and $\text{Cl}_2$?

May/June 2016

An ethanol burner may be used to warm water. If the relevant measurements are recorded, a value for the enthalpy of combustion of ethanol can be worked out. The equation $\text{heat transferred} = -mc\Delta T$ is used as part of the calculation. Which symbols are correctly described?

May/June 2016

The equation for the complete combustion of propan-1-ol is given below. $\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}(l) + 4\frac{1}{2}\,\text{O}_2(g) \rightarrow 3\text{CO}_2(g) + 4\text{H}_2\text{O}(l)$ Standard enthalpy changes of formation are provided. What is the standard enthalpy change of combustion of propan-1-ol, in $\text{kJ mol}^{-1}$?

May/June 2016

Enthalpy changes, $\Delta H$, may be either positive or negative. Which row is the correct one?

May/June 2016

A pair of students, $P$ and $Q$, had to sketch bar charts to show how the sizes of certain properties of the halogens and their compounds vary. Their sketches are given. The bar charts indicate only the pattern of change, not the real numerical values. Student $P$: solubility of $\text{AgX}(s)$ in $\text{NH}_3(aq)$. Student $Q$: $\Delta H^\circ$ for $\text{H}_2(g) + X_2(g) \rightarrow 2\text{HX}(g)$. Which of the students have produced bar charts that display the trends correctly?

May/June 2016

A reaction pathway diagram is displayed. The four reactions that come next are all exothermic. Which reaction would not be expected to have a pathway like this?

May/June 2016

Methanol can be made by reacting carbon monoxide with hydrogen. $\text{CO(g)} + 2\text{H}_2\text{(g)} \rightarrow \text{CH}_3\text{OH(g)}$ The average bond energies needed are shown below: $E(\text{C} \equiv \text{O}) = 1077\,\text{kJ mol}^{-1}$ $E(\text{C-O}) = 360\,\text{kJ mol}^{-1}$ $E(\text{C-H}) = 410\,\text{kJ mol}^{-1}$ $E(\text{H-H}) = 436\,\text{kJ mol}^{-1}$ $E(\text{O-H}) = 460\,\text{kJ mol}^{-1}$ What is the enthalpy change for this reaction?

May/June 2016

The reaction between carbon and oxygen is given. $\text{C(s)} + \frac{1}{2}\,\text{O}_2(\text{g}) \rightarrow \text{CO(g)}$ Which description best matches the enthalpy change for this reaction?

May/June 2017

Which expression represents the standard enthalpy change of combustion of methane?

May/June 2017

Which of the following statements concerning endothermic reactions are correct?

May/June 2017

Use the data below for this question. $\Delta H_f^\circ(\text{CO(g)}) = -111\,\text{kJ mol}^{-1}$ $\Delta H_f^\circ(\text{CO}_2\text{(g)}) = -394\,\text{kJ mol}^{-1}$ $\Delta H_f^\circ(\text{Fe}_2\text{O}_3\text{(s)}) = -822\,\text{kJ mol}^{-1}$ Iron(III) oxide reacts with carbon monoxide. $3\text{CO(g)} + \text{Fe}_2\text{O}_3\text{(s)} \rightarrow 3\text{CO}_2\text{(g)} + 2\text{Fe(s)}$ Calculate the enthalpy change when $55.8\,\text{g}$ of iron are produced by this reaction?

May/June 2017

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

May/June 2018

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

May/June 2018

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

May/June 2018

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

May/June 2018

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

May/June 2018

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

May/June 2018

When the temperature is $550\,^{\circ}\text{C}$, nitrogen dioxide reacts with unburnt hydrocarbon fragments such as $\text{CH}_3$ inside the catalytic converter of a motor vehicle. $\text{4CH}_3 + \text{7NO}_2 \rightarrow 3\tfrac{1}{2}\text{N}_2 + 4\text{CO}_2 + 6\text{H}_2\text{O}$ Which row indicates the energy change for this reaction and a plausible explanation for it?

May/June 2019

Which of these statements about enthalpy changes are correct?

May/June 2019

The following two reactions are given together with their enthalpy changes. $2\text{C}(s) + 2\text{H}_2(g) \rightarrow \text{C}_2\text{H}_4(g) \quad \Delta H^\circ = +52.2\,\text{kJ mol}^{-1}$ $\text{C}_2\text{H}_2(g) + \text{H}_2(g) \rightarrow \text{C}_2\text{H}_4(g) \quad \Delta H^\circ = -175.8\,\text{kJ mol}^{-1}$ The information above may be used to determine the enthalpy change for the reaction below. $2\text{C}(s) + \text{H}_2(g) \rightarrow \text{C}_2\text{H}_2(g) \quad \Delta H^\circ = X$ What is the value of $X$?

May/June 2019

A reaction pathway diagram is displayed. Which row is the correct one?

May/June 2019

Which enthalpy changes always have a negative value of $\Delta H$?

May/June 2019

A reaction pathway diagram for a chemical reaction is shown. Which statement is correct?

May/June 2019

The following two reactions are given. $\text{H}_2(g) \rightarrow 2\text{H}(g)$ $\text{CO}(g) + \tfrac{1}{2}\text{O}_2(g) \rightarrow \text{CO}_2(g)$ When molar quantities are taken, how may the two energy changes linked to these reactions be identified?

May/June 2020

Which reactions would produce the reaction profile shown?

May/June 2020

In solid sulfur, the particles are $\text{S}_8$ molecules. Which equation shows the standard enthalpy of atomisation of sulfur?

May/June 2020

Gaseous sodium ions may be produced from sodium atoms. $\text{Na(s)} \rightarrow \text{Na}^+(\text{g})$ Which quantities must be used to work out the enthalpy change of formation of $\text{Na}^+(\text{g})$?

May/June 2020

The enthalpy changes for two reactions are given below. $\text{K}_2\text{CO}_3(s) + 2\text{HCl}(aq) \rightarrow 2\text{KCl}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g) \quad \Delta H = -34.0\,\text{kJ mol}^{-1}$ $\text{KHCO}_3(s) + \text{HCl}(aq) \rightarrow \text{KCl}(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g) \quad \Delta H = +32.8\,\text{kJ mol}^{-1}$ Determine the enthalpy change for the reaction shown below. $2\text{KHCO}_3(s) \rightarrow \text{K}_2\text{CO}_3(s) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$

May/June 2020

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 $\text{Cl}^-(aq) \rightarrow \text{Cl}(g) + aq$

May/June 2021

$\Delta H_1^\circ$ 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 $\Delta H_c^\circ$?

May/June 2021

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?

May/June 2021

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

May/June 2021