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.

This question is about the noble gas xenon.

Xenon is unreactive.

Explain, in terms of its electronic configuration, why xenon is unreactive.

Under extreme conditions, xenon can be made to react with fluorine to form xenon tetrafluoride, XeF₄.

Write the balanced equation for this reaction.

Some information about xenon tetrafluoride is shown in Figure 3.

State and explain, with reasons, the type of structure and bonding in xenon tetrafluoride.

Under extreme conditions, xenon reacts with fluorine to form xenon hexafluoride.

The reaction is exothermic. The energy change for the reaction is –400 kJ mol^–1.

On Figure 4

• add a label to the y‑axis

• draw the reaction profile for this reaction

• label the energy change and the activation energy for the reaction.

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 3 shows the apparatus that is used.

State what is used to measure the temperature change in Figure 3.

State one reason for using the piece of equipment A in Figure 3.

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 4 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.

Figure 5 shows the structure of one molecule of three different compounds, X, Y and Z.

The molecules of the compounds shown in Figure 5 all contain the same number of carbon atoms.

Give the number of carbon atoms in a molecule of compound X.

Compound X contains carbon and one other element.

Give the name of the other element in compound X.

Which of the compounds in Figure 5 is a hydrocarbon?

Which of the compounds in Figure 5 have the same molecular formula?

Figure 6 shows where fractions are produced in the fractional distillation of crude oil.

Complete the sentences about fractions obtained from crude oil.

The fraction with the smallest molecules is called_........ .

Compared to petrol, the boiling point of kerosene is_........ .

When petrol burns, one product is_........ .

When some impure hydrocarbon fuels are burned, sulfur dioxide is one of the products.

Some sulfur dioxide gas is dissolved in water to form solution W.

When solution W is added to sodium hydroxide solution of pH 12

• the pH changes

• the temperature increases.

Explain how the pH changes and why the temperature increases.

For steps 2 and 3, the student obtained the mass measurements shown in Figure 4 for the first salt.

Use the mass measurements in Figure 4 to calculate the mass of salt, in grams, added to the water.

mass of salt =_........ g

The student repeated the method for three different salts, A, B and C.

The same mass of each salt was used.

Figure 5 shows the temperature readings obtained for the three different salts.

Calculate the temperature change for salt C.

Include a sign to show if the temperature change is an increase or a decrease.

temperature change =_........ °C

Explain which salt produces the biggest exothermic change.

Explain why a polystyrene cup is a better container to use for this investigation than a glass beaker.

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 3 shows the apparatus that is used.

Give the letter of the piece of apparatus, A, B, C or D, in Figure 3 that is used to measure the temperature.

Give the name of the piece of apparatus B shown in Figure 3.

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 4.

Calculate the change in temperature.

Give a sign and a unit in your answer.

temperature change =_........

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

Give the formula and the name of the solid.

formula_........

name_........

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⁻³

Dissolving ammonium chloride in water is an endothermic process. Figure 10 shows part of the reaction profile for this process.

Explain how Figure 10 shows that dissolving ammonium chloride in water is an endothermic process.

Complete the reaction profile in Figure 10 and label the activation energy.

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^–3

Dissolving ammonium chloride in water is an endothermic process. Figure 1 shows part of the reaction profile for this process.

Explain how Figure 1 shows that dissolving ammonium chloride in water is an endothermic process.

Complete the reaction profile in Figure 1 and label the activation energy.

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 2.

State how the results in Figure 2 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 3.

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 4 shows the reaction profile for this reaction.

Use the words from the box to complete the labels on Figure 4.

The first four elements in group 1 are lithium, sodium, potassium and rubidium.

Rubidium reacts with water to form rubidium hydroxide and hydrogen.

Predict what you would see when a small piece of rubidium is placed in a large volume of water.

Why is rubidium more reactive than potassium?

8.5 g of rubidium are reacted completely with water.

The reaction makes a solution of rubidium hydroxide. The volume of this solution is 2.5 dm³.

Calculate the concentration of the rubidium hydroxide solution in g dm^–3.

(relative atomic mass: Rb = 85; relative formula mass: RbOH = 102)

concentration =_........ g dm^–3

An example of an endothermic reaction is the reaction between rubidium hydroxide and ammonium carbonate, (NH₄)₂CO₃.

This reaction forms rubidium carbonate, Rb₂CO₃, ammonia and one other product.

Write the balanced equation for this reaction.

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.

volume of solution =_........ cm³

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 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.