Exothermic & endothermic reactions

A student investigates the temperature change when 10 g of solid magnesium chloride is dissolved in 100 cm³ of water.

Figure 2 shows the apparatus the student uses.

Name the piece of apparatus labelled X in Figure 2.

The student carries out the following steps

step 1 measure the initial temperature of the water in the beaker

step 2 add the magnesium chloride

step 3 stir the mixture

step 4 record the new temperature.

State why the mixture is stirred in step 3.

State two ways the apparatus could be changed to reduce the heat energy lost during the investigation.

The student carries out the experiment three times.

Figure 3 shows the results.

Calculate the mean temperature change for this investigation.

Explain, using the information in Figure 3, the type of reaction that occurs when magnesium chloride dissolves in water.

In one reaction the temperature of the reaction mixture decreases.

Which word describes this type of reaction?

In an experiment, a salt is dissolved in water.

The temperature change is measured.

Figure 7 shows the apparatus that is used.

State what is used to measure the temperature change in Figure 7.

State one reason for using the piece of equipment A in Figure 7.

A student suggests putting a lid on piece of equipment B.

State why this would help to give a more accurate value for the temperature change.

Four different salts, P, Q, R and S, are dissolved in water.

Figure 8 shows the starting temperature of the water and the final temperature of the solution after the salt dissolves.

Complete the table

• to show the temperature changes when salt R and salt S dissolve

• by placing a tick (✓) in the box, on the bottom row, for the salt that absorbs the most heat energy when it dissolves.

One of the salts dissolved is barium chloride, BaCl₂.

Barium chloride contains the chloride ion, Cl^–.

Give the formula of the barium ion in barium chloride.

This question is about bromine.

Give the colour and physical state of bromine at room temperature.

Bromine reacts with hydrogen to form hydrogen bromide.

Write the word equation for this reaction.

Hydrogen bromide dissolves in water to form a solution.

This solution of hydrogen bromide reacts with alkalis.

State the type of reaction that occurs when a solution of hydrogen bromide reacts with an alkali.

Bromine and the other halogens react with hot iron wool.

Figure 11 shows the relative speed of some of these reactions.

Fluorine also reacts with hot iron wool.

Use Figure 11 to predict the relative speed of this reaction.

Potassium bromide contains 32.8% potassium by mass.

Calculate the mass of potassium and the mass of bromine in 500 g potassium bromide.

Some reactions are exothermic and some reactions are endothermic.

What does an exothermic reaction always give out?

In an experiment, a solid is mixed with a liquid. The temperature change of the mixture is measured.

Figure 6 shows the apparatus that is used.

Give the letter of the piece of apparatus, A, B, C or D, in Figure 6 that is used to measure the temperature.

Give the name of the piece of apparatus B shown in Figure 6.

The piece of apparatus labelled C is made from polystyrene.

State why polystyrene is a better material than glass for this piece of apparatus.

The results of the experiment are given in Figure 7.

Calculate the change in temperature.

Give a sign and a unit in your answer.

The solid used in this experiment contained only NH⁺₄ ions and NO^–₃ ions.

Give the formula and the name of the solid.

The concentration of a solution can be calculated using the equation

A student dissolved 9.25 g of ammonium chloride in water and made up the

Use the equation to calculate the concentration of this solution in gdm⁻³.

concentration =_........ g dm

Dissolving ammonium chloride in water is an endothermic process. Figure 17 shows part of the reaction profile for this process.

Explain how Figure 17 shows that dissolving ammonium chloride in water is an endothermic process.

Complete the reaction profile in Figure 17 and label the activation energy.

A student used the equipment in Figure 18 to investigate whether electricity can pass through solid ammonium chloride and through ammonium chloride solution.

If an electrical current flows in the circuit, the lamp will light up.

Figure 19 shows the results of the investigation.

Explain the results of the investigation.

Ammonia gas is toxic.

Which symbol should be placed on a container of a toxic gas?

Give one safety precaution that should be taken when working with toxic gases in the laboratory.

The concentration of a solution can be calculated using the equation

A student dissolved 9.25 g of ammonium chloride in water and made up the

Use the equation to calculate the concentration of this solution in gdm⁻³.

concentration =_........ g dm

Dissolving ammonium chloride in water is an endothermic process. Figure 2 shows part of the reaction profile for this process.

Explain how Figure 2 shows that dissolving ammonium chloride in water is an endothermic process.

Complete the reaction profile in Figure 2 and label the activation energy.

A student used the equipment in Figure 3 to investigate whether electricity can pass through solid ammonium chloride and through ammonium chloride solution.

If an electrical current flows in the circuit, the lamp will light up.

Figure 4 shows the results of the investigation.

Explain the results of the investigation.

A student investigated the reaction between potassium iodide and lead nitrate.

Solutions of potassium iodide and lead nitrate were mixed together. Lead iodide and potassium nitrate were formed.

Complete the word equation.

The student recorded the total mass of the reactants and the total mass of the products.

The results are shown in Figure 4.

State how the results in Figure 4 show that mass is conserved in this reaction.

In another experiment, a student investigated the temperature decrease when different amounts of ammonium nitrate crystals were dissolved in 100 cm³ of water.

The apparatus used is shown in Figure 5.

The student used the following method.

step N $pour 100 cm³ of water into the polystyrene cup

step 2 add one spatula of ammonium nitrate crystals to the water

step 3 stir the mixture

step 4 use the thermometer to record the lowest temperature reached by the mixtur e

step 5 repeat steps 1 to 4 using different amounts of ammonium nitrate

Name a piece of apparatus that should be used to measure the 100 cm³ of water in step 1.

The student cannot work out the temperature decrease using the method described.

State what the student must do before step 2 to be able to work out the temperature decrease.

State why a polystyrene cup is used in this experiment.

Figure 6 shows the reaction profile for this reaction.

Use the words from the box to complete the labels on Figure 6.

A student poured 50 cm³ water into a beaker and measured the water’s temperature.

The student added 1.00 g calcium chloride to the water, stirred the mixture and then recorded the temperature.

Give the name of the apparatus that could be used to measure 1.00 g of calcium chloride.

The student’s results were

temperature of water at start = 21C temperature of mixture after stirring = 32C

Explain, using these results, the type of heat energy change that occurs when calcium chloride dissolves in water.

Calcium chloride is hazardous to health.

Which hazard symbol would be expected to be seen on a container of calcium chloride?

Give a safety precaution that the student should take during the experiment.

State one way in which the apparatus could be changed to reduce the amount of heat energy lost during the experiment.

The concentration of a calcium chloride solution is 12 g dm^–3.

Calculate the volume of this solution, in cm³, that contains 9.0 g of calcium chloride.

You must show your working.

Students are investigating exothermic and endothermic reactions. They are finding the temperature change in 50 cm³ water when a solid dissolves in it. The apparatus is shown in Figure 1.

The steps needed to carry out this experiment are P, Q, R, S and T. They are shown below.

They are not in the correct order.

P pour the 50 cm³ water into the polystyrene cup Q add the solid to the water and stir R measure 50 cm³ water using a beaker S measure the initial temperature of the water T measure the final temperature of the solution when all the solid has dissolved

Write the steps in the correct order, from left to right.

The dissolving of this solid in water is an exothermic change. The experiment is repeated a number of times. Compared with the initial temperature of the water, the final temperature of the solution is

State how step R could be changed to measure the volume of water more accurately.

Figure 2 shows a cold pack.

When the pack is squeezed hard the inner bag bursts. Then the pack goes cold.

Explain why the pack goes cold.

Give the reason why the pack can be used only once.

Ethanol can be used as a liquid fuel.

A student investigates how much heat energy is released when a known mass of ethanol is burned.

The apparatus is set up as shown in Figure 15.

A known volume of water is placed in a metal can. The temperature of the water is measured. The ethanol is ignited and placed under the beaker so that the flame is touching the beaker. The water is heated by the flame. The flame is extinguished. The final temperature of the water is measured.

The theoretical temperature rise for burning a given mass of ethanol is 82.4 °C.

In the experiment the actual temperature rise for burning this mass of ethanol was only 34.8 °C. One reason why the temperature rise is less than expected is that the ethanol does not burn completely.

Give a reason why, even if the ethanol burns completely, the actual temperature rise is much less than the theoretical value.

Explain how the method described above could be improved to give a temperature rise closer to the theoretical value.

The amount of heat energy used to raise the temperature of the water by 34.8 °C can be calculated using

heat energy = 210 × temperature rise

Calculate the amount of heat energy used.

heat energy =_........ (energy units)

Propanol and butanol are both members of the same homologous series as ethanol.

H H H
H H H H

H H H
H H H H

propanol butanol

Propanol and butanol can also be burned in the apparatus shown in Figure 15.

Give three reasons why ethanol, propanol and butanol are members of the same homologous series.

Ethanol can oxidise when exposed to air to produce ethanoic acid and water. Propanol can also oxidise in a similar reaction when it is exposed to air.

Write the word equation for the reaction when propanol oxidises when it is exposed to air.

What is the formula of the functional group in carboxylic acids?

Ethanol can be used as a liquid fuel.

A student investigates how much heat energy is released when a known mass of ethanol is burned.

The apparatus is set up as shown in Figure 3.

A known volume of water is placed in a metal can. The temperature of the water is measured. The ethanol is ignited and placed under the beaker so that the flame is touching the beaker. The water is heated by the flame. The flame is extinguished. The final temperature of the water is measured.

The theoretical temperature rise for burning a given mass of ethanol is 82.4 °C.

In the experiment the actual temperature rise for burning this mass of ethanol was only 34.8 °C. One reason why the temperature rise is less than expected is that the ethanol does not burn completely.

Give a reason why, even if the ethanol burns completely, the actual temperature rise is much less than the theoretical value.

Explain how the method described above could be improved to give a temperature rise closer to the theoretical value.

The amount of heat energy used to raise the temperature of the water by 34.8 °C can be calculated using

heat energy = 210 × temperature rise

Calculate the amount of heat energy used.

heat energy =_........ (energy units)

Ethanol can oxidise when exposed to air to produce ethanoic acid and water. Propanol can also oxidise in a similar reaction when it is exposed to air.

Write the word equation for the reaction when propanol oxidises when it is exposed to air.

What is the formula of the functional group in carboxylic acids?