Exothermic and endothermic reactions

Which statement about reactions that release heat is incorrect?

Feb/March 2016

Which change shown on the diagram includes combustion? Not all of the reaction products are displayed on the diagram.

Feb/March 2016

Which row gives a description of an endothermic reaction?

Feb/March 2016

The diagram illustrates an energy level diagram for a reaction. From the diagram, it can be seen that the reaction is ......1...... . Raising the temperature increases the rate of reaction. One reason for this is that the ......2...... . Which words correctly fill gaps 1 and 2?

Feb/March 2016

Ammonium chloride is put into $100\,\text{cm}^3$ of water. The temperature falls from $25^\circ\text{C}$ to $20^\circ\text{C}$. What type of reaction takes place?

Feb/March 2017

The energy change for an exothermic reaction is represented in the diagram below. Which reactions would this diagram fit?

Feb/March 2017

A student did two experiments. experiment 1: The student heated a limestone sample very strongly. A white powder was formed. experiment 2: The white powder from experiment 1 was allowed to cool. The student then added a little cold water to the powder. Large amounts of steam were given off. Which statement is incorrect?

Feb/March 2017

Ammonia is produced when nitrogen reacts with hydrogen in the presence of an iron catalyst. This reaction is exothermic. The reaction equation is given below. $\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3$. The bond energies are listed in the table. What is the energy released in this reaction?

Feb/March 2017

The energy level diagram for the reaction in which P and Q react to produce R and S is shown. Which row states the energy changes involved and the reaction type?

Feb/March 2017

The diagram shows a match. When the match is struck, a chemical reaction occurs. Which row gives the description of the chemical reaction?

Feb/March 2018

The energy level diagram for the reaction of $X_2(g)$ with $Y_2(g)$ to produce $XY$ gas is shown. Which statement is correct?

Feb/March 2018

Methane reacts with oxygen to produce carbon dioxide and water. $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$ The bond energies are listed in the table below. What is the energy change for this reaction?

Feb/March 2018

Statement 1: Hydrogen is used as a fuel. Statement 2: As hydrogen burns in air and forms water, heat energy is released. Which statement is correct?

Feb/March 2018

A sample of 10 g of ammonium nitrate is put into water at $25\degree\text{C}$, and the mixture is stirred. The ammonium nitrate dissolves, and after one minute the temperature of the solution becomes $10\degree\text{C}$. Which word describes this change?

Feb/March 2019

10 g of ammonium nitrate is put into water at $25^{\circ}\text{C}$ and the mixture is stirred. The ammonium nitrate dissolves and, after one minute, the solution temperature is $10^{\circ}\text{C}$. Which word describes this change?

Feb/March 2019

Hydrogen undergoes reaction with chlorine as shown by the equation: $\text{H}_2(\text{g}) + \text{Cl}_2(\text{g}) \rightarrow 2\text{HCl}(\text{g})$. This reaction gives out heat. Which statement about this reaction is correct?

Feb/March 2019

Which energy level diagram represents the reaction that releases the greatest amount of energy?

Feb/March 2020

Nitrogen trifluoride, $\text{NF}_3$, is employed in the production of some kinds of solar panels. The equation for the formation of nitrogen trifluoride is shown: $\text{N}_2 + 3\text{F}_2 \rightarrow 2\text{NF}_3$. Using the table of bond energies, what energy change does this reaction have?

Feb/March 2020

Which row identifies an endothermic reaction?

Feb/March 2021

Which row gives the description of an endothermic reaction?

Feb/March 2021

The equation below represents the complete combustion of methane. $\text{CH}_4\text{(g)} + 2\text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} + 2\text{H}_2\text{O( g)}$ The bond energies are listed in the table. What is the energy change for this reaction?

Feb/March 2021

A reaction pathway diagram for the reaction is displayed. Which of the following statements about the reaction are correct?

Feb/March 2023

If powdered sodium carbonate is added to aqueous ethanoic acid, the temperature of the resulting mixture goes down. Which statement about this reaction is correct?

Feb/March 2023

The balanced equation for the complete combustion of ethyne, $\text{H-C} \equiv \text{C-H}$, is given below. $2\text{H-C} \equiv \text{C-H} + 5\text{O}=\text{O} \rightarrow 4\text{O}=\text{C}=\text{O} + 2\text{H-O-H}$ A list of bond energies is provided. What is the enthalpy change for the reaction when $1\,\text{mol}$ of ethyne is completely burned?

Feb/March 2024

There are four statements about photosynthesis below. Which of these statements are correct?

Feb/March 2024

As dilute sulfuric acid reacts with aqueous sodium hydroxide, the temperature of the solution increases. Which terms are used to describe this reaction?

Feb/March 2025

The reaction pathway diagram for the reaction between P and Q to produce R and S is shown. Which letter shows the enthalpy change for the reaction?

Feb/March 2025

The equation for the complete combustion of methane is given below. $\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(g)$ Some bond energies are shown in the table. Calculate the enthalpy change for this reaction.

Feb/March 2025

An energy level diagram for the reaction of sodium hydrogen carbonate with dilute hydrochloric acid is shown. Which row gives the correct description of the reaction type and the energy of the reactants and products?

May/June 2016

An energy level diagram for the reaction between magnesium and hydrochloric acid is shown. Which of the statements about the reaction is incorrect?

May/June 2016

The energy level diagram indicates the energies of the reactants and products in a chemical reaction. Which row gives the correct energy change and the type of reaction shown?

May/June 2016

When hydrogen reacts with oxygen, it burns exothermically. The reaction is represented by $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$. The table lists the bond energies involved. What amount of energy is released in this reaction?

May/June 2016

An energy level diagram for the combustion of methane is displayed. Which row shows the equation and energy change for this reaction?

May/June 2016

Hydrazine, $\text{N}_2\text{H}_4$, breaks down as illustrated to give $\text{N} \equiv \text{N}$ and $2\text{H}-\text{H}$. The energy change for this reaction is $-95\,\text{kJ mol}^{-1}$. The table gives some of the bond energies involved. Calculate the bond energy of the $\text{N}-\text{N}$ bond.

May/June 2016

Which of these statements about exothermic and endothermic reactions are correct?

May/June 2017

Which of these statements about exothermic and endothermic reactions are correct?

May/June 2017

Heat is given out when hydrocarbons react with air. Which equations show this?

May/June 2017

Which statements about exothermic and endothermic reactions are correct?

May/June 2017

Which of the following statements about exothermic and endothermic reactions are correct?

May/June 2017

Chlorine combines with ethane to form chloroethane and hydrogen chloride. $\text{C}_2\text{H}_6 + \text{Cl}_2 \rightarrow \text{C}_2\text{H}_5\text{Cl} + \text{HCl}$ This reaction gives out heat. The bond energies are listed in the table below. C-Cl: $+340\,\text{kJ mol}^{-1}$ C-C: $+350\,\text{kJ mol}^{-1}$ C-H: $+410\,\text{kJ mol}^{-1}$ Cl-Cl: $+240\,\text{kJ mol}^{-1}$ H-Cl: $+430\,\text{kJ mol}^{-1}$ Calculate the energy change for the reaction.

May/June 2017

Photosynthesis and respiration are key natural processes. Which statement is true?

May/June 2017

Which of the statements about exothermic and endothermic reactions are correct?

May/June 2017

The reaction equation for hydrogen reacting with chlorine is shown below. $\text{H}_2(g) + \text{Cl}_2(g) \rightarrow 2\text{HCl}(g)$ This reaction gives out heat. The bond energies are listed in the table. $\text{Cl--Cl}$: $+240\ \text{kJ mol}^{-1}$ $\text{H--Cl}$: $+430\ \text{kJ mol}^{-1}$ $\text{H--H}$: $+436\ \text{kJ mol}^{-1}$ Determine the energy change for this reaction.

May/June 2017

Which of the following statements about exothermic and endothermic reactions are correct?

May/June 2017

Hydrogen reacts with chlorine to produce hydrogen chloride. This reaction releases heat. $\text{H}_2(\text{g}) + \text{Cl}_2(\text{g}) \rightarrow 2\text{HCl}(\text{g})$ The overall energy change for this reaction is $-184\ \text{kJ mol}^{-1}$. The table lists some of the bond energies involved. H-Cl: $+430\ \text{kJ mol}^{-1}$ H-H: $+436\ \text{kJ mol}^{-1}$ What is the Cl-Cl bond energy?

May/June 2017

The burning of fuels is an exothermic reaction. What does the term exothermic mean?

May/June 2018

What is given out when any fuel is burned?

May/June 2018

Solid R was added to dilute sulfuric acid. The starting temperature of the dilute sulfuric acid and the temperature of the resulting solution are given. What was the temperature change in $^{\circ}\text{C}$?

May/June 2018

Plant cells use energy from sunlight during photosynthesis. Which row gives the description and explanation of the energy change that happens?

May/June 2018

Hydrogen bromide breaks down to produce hydrogen and bromine: $2\text{HBr(g)} \rightarrow \text{H}_2\text{(g)} + \text{Br}_2\text{(g)}$. The bond energies are provided. What is the energy change for this reaction?

May/June 2018

Which diagram shows the correctly labelled energy level diagram for an endothermic reaction?

May/June 2018

The equation for the complete combustion of methane is given below. $\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(g)$ The bond energies are listed in the table. What is the energy change for the reaction?

May/June 2018

Details of two reactions are provided. • The neutralisation reaction between citric acid and sodium hydrogencarbonate is endothermic. • The displacement reaction between magnesium and carbon dioxide is exothermic. Which of the following statements about these two reactions are correct?

May/June 2018

Ethene reacts with hydrogen. The equation is given below. $\text{CH}_2{=}\text{CH}_2 + \text{H}_2 \rightarrow \text{C}_2\text{H}_6$ The table shows the bond energies. The reaction gives out heat. Calculate the energy change for the reaction?

May/June 2018

Solid R was reacted with dilute sulfuric acid. The starting temperature of the dilute sulfuric acid and the end temperature of the solution are shown. What was the temperature change in ^{\circ}C?

May/June 2018

Dissolving ammonium chloride in water is an endothermic change. Which row gives the energy change and temperature change of the mixture while ammonium chloride is dissolving?

May/June 2019

Which row gives the energy-level diagram and the energy change for an exothermic reaction?

May/June 2019

Nitrogen combines with hydrogen to make ammonia. $\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3$ This reaction releases heat. The bond energies are listed in the table. Bond energies (in $\text{kJ/mol}$): - $\text{N}\equiv\text{N}$: $945$ - $\text{H}-\text{H}$: $436$ - $\text{N}-\text{H}$: $390$ Calculate the energy change for this reaction.

May/June 2019

Two elements, X and Y, combine to make a covalent molecule, as illustrated. This reaction gives out heat. $\text{X}_2(g) + \text{Y}_2(g) \rightarrow 2\text{XY}(g)$ The bond energies are listed in the table. What is the energy change for this reaction?

May/June 2019

Methane reacts with oxygen during combustion to produce carbon dioxide and water. $\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(l)$ The bond energies are listed in the table. What is the energy change for this reaction?

May/June 2019

Complete combustion of propane is exothermic. The reaction equation is shown here. $\text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow 3\text{CO}_2 + 4\text{H}_2\text{O}$ Which energy-level diagram shows the complete combustion of propane?

May/June 2021

What changes take place when hydrogen is combusted in oxygen?

May/June 2021

Four different fuels are burned to warm a beaker of water for the same length of time, using the apparatus shown. The water’s starting temperature and the temperature after heating by each fuel are measured. Which fuel gives out the greatest amount of heat energy?

May/June 2021

Heat energy transfer in chemical reactions may be represented by energy level diagrams. In which row is the description correct?

May/June 2021

The equations for two reactions are given below. 1. $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$ 2. $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$ Which statement about these reactions is correct?

May/June 2021

Complete combustion of propane is an exothermic reaction. The reaction is represented by this equation: $\text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow 3\text{CO}_2 + 4\text{H}_2\text{O}$ Which energy level diagram shows the complete combustion of propane?

May/June 2021

Four different fuels are used, each for the same length of time, to heat a beaker of water with the apparatus shown. The water’s starting temperature and its temperature after heating with each fuel are measured. Which fuel gives out the greatest amount of heat energy?

May/June 2021

The equation represents the reaction of hydrogen with oxygen. $2\text{ H-H} + \text{O=O} \rightarrow 2\text{ H-O-H}$ The bond energies are listed. $\text{H-H} = 436\,\text{kJ mol}^{-1}$ $\text{O=O} = 495\,\text{kJ mol}^{-1}$ $\text{O-H} = 463\,\text{kJ mol}^{-1}$ Which row gives the energy change and reaction type?

May/June 2021

The equation for the breakdown of hydrogen iodide is shown below. $\text{2HI} \rightarrow \text{H}_2 + \text{I}_2$ Some bond energies are listed. H-H: $440\,\text{kJ/mol}$ I-I: $150\,\text{kJ/mol}$ H-I: $300\,\text{kJ/mol}$ What is the energy change for this reaction?

May/June 2021

An energy level diagram for a reaction is displayed. Which statement is correct?

May/June 2022

The equation for the reaction of gaseous hydrogen with gaseous iodine to produce gaseous hydrogen iodide is shown: $\text{H}_2(g) + \text{I}_2(g) \rightarrow 2\text{HI}(g)$ This reaction is exothermic. Which statement accounts for the fact that the reaction is exothermic?

May/June 2022

On the energy level diagram, which arrow indicates the total energy change for an endothermic reaction?

May/June 2022

A reaction pathway diagram is given. Which statement about this reaction is correct?

May/June 2023

Which statement refers to an exothermic reaction?

May/June 2023

Which process includes combustion? (Some of the reaction products are not labelled in the diagram.)

May/June 2023

Ethene gas, $\text{C}_2\text{H}_4$, is fully combusted in excess oxygen so that carbon dioxide and water are produced. The equation for this exothermic reaction is shown below. $\text{C}_2\text{H}_4 + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 2\text{H}_2\text{O}$ The table gives the bond energies for the bonds involved in the reaction. What is the total energy change in this reaction?

May/June 2023

What equation represents photosynthesis?

May/June 2023

Methane is burned in excess oxygen. The equation is given as: $\text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(g)$. Bond energies are shown. What is the energy change for this reaction?

May/June 2023

The reaction pathway diagram for an exothermic reaction is shown. Which row correctly names labels 1, 2, 3 and 4?

May/June 2023

The complete combustion equation for ethene is given here: $\text{C}_2\text{H}_4(\text{g}) + 3\text{O}_2(\text{g}) \rightarrow 2\text{CO}_2(\text{g}) + 2\text{H}_2\text{O}(\text{g})$. A selection of bond energies is provided. What is the total energy change when 1 mole of ethene is fully combusted?

May/June 2023

Which row shows what occurs in an endothermic reaction?

May/June 2024

Water is mixed with anhydrous copper(II) sulfate. Which row shows the direction of energy change and the colour change of the mixture as the reaction takes place?

May/June 2024

Three reactions are given. Which of the reactions are endothermic?

May/June 2024

Which statements about endothermic reactions are correct?

May/June 2024

When hydrogen reacts with oxygen, $486\,\text{kJ mol}^{-1}$ of energy is released. $\text{2H}_2(g) + \text{O}_2(g) \rightarrow \text{2H}_2\text{O}(g)$ The H-H bond energy is $436\,\text{kJ mol}^{-1}$ and the H-O bond energy is $464\,\text{kJ mol}^{-1}$. Determine the bond energy of O=O.

May/June 2024

Which reaction pathway diagram represents the reaction that releases the greatest amount of energy? The y-axis uses the same scale in every diagram.

May/June 2024

During photosynthesis, plant cells obtain energy from sunlight. Which row describes the energy change that takes place and explains it?

May/June 2024

Two separate experiments are carried out to determine the enthalpy change, $\Delta H$, for each reaction. The temperature of each reaction mixture is recorded at the start of the reaction and again after 3 minutes. Which row shows the correct sign of the value of $\Delta H$ for each experiment and states whether the reaction is endothermic or exothermic?

May/June 2024

Three statements concerning energy changes in chemical reactions are given. 1 For an endothermic reaction, the temperature of the surroundings rises. 2 For an exothermic reaction, thermal energy is absorbed from the surroundings. 3 On the reaction pathway diagram for an exothermic reaction, the products are at a lower energy level than the reactants. Which statements are correct?

May/June 2025

Which reaction pathway diagram shows the greatest rise in the temperature of the surroundings? (The scale on the y-axis is identical in each diagram.)

May/June 2025

When ammonium nitrate is mixed with water, the temperature of the mixture falls. The ammonium nitrate can be obtained again by removing the water through evaporation. Which statement accounts for these observations?

May/June 2025

Water is poured onto anhydrous copper(II) sulfate in a test-tube. The mixture turns hot. Which reaction type and reaction pathway diagram are appropriate for this reaction?

May/June 2025

A reaction pathway diagram is shown. Which row identifies the reaction type and the way the temperature of the surroundings changes during the reaction?

May/June 2025

The mean bond energy for the C-H bond is $413\ \text{kJ mol}^{-1}$. What is the enthalpy change when $1.0\ \text{mol}$ of methane molecules is made from carbon and hydrogen atoms?

May/June 2025

Which row gives the description of an exothermic reaction?

May/June 2025

A reaction pathway diagram is shown. Which row gives the correct labels for X and Y and identifies the type of reaction occurring?

May/June 2025

This question concerns energy changes during reactions.

May/June 2025

This question concerns chemical reactions and the energy changes they produce.

May/June 2025

When anhydrous copper(II) sulfate is added to water, a solution forms and heat is released. Which row indicates the temperature change and the reaction type occurring?

Oct/Nov 2016

When element X undergoes combustion, a large amount of energy is released. What is X?

Oct/Nov 2016