Reaction profiles

Metals react with acids to produce a salt and a gas.

Which salt is produced when magnesium reacts with hydrochloric acid?

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Which gas is produced when magnesium reacts with hydrochloric acid?

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A student investigated the temperature change in the reaction between metals and hydrochloric acid.

This is the method used.

1. Measure 25 cm³ of hydrochloric acid at 20 °C into a container.

2. Add 1 g of a metal.

3. Record the temperature change.

4. Repeat steps 1 to 3 using a different metal.

Draw one line from the type of variable to the name of the variable in the investigation.

Which container would be the most suitable to reduce energy transfer with the surroundings?

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Figure 1 shows part of the scale of the thermometer used in the investigation.

What is the resolution of the thermometer?

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The reaction between a metal and an acid is exothermic.

What happens to the temperature of the mixture during the reaction?

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Figure 2 shows the reaction profile for the reaction between a metal and an acid.

Which letter in Figure 2 represents the reactants?

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Which letter in Figure 2 represents the activation energy?

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Which letter in Figure 2 represents the overall energy change?

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This question is about propane (C₃H₈).

Figure 7 shows the displayed structural formula of propane.

Explain why propane has a low boiling point.

Propane reacts with oxygen to produce carbon dioxide and water.

The reaction is exothermic.

Figure 8 shows four reaction profiles.

Which is the correct reaction profile and labels for the reaction between propane and oxygen?

Tick () one box.

Figure 9 shows the displayed formula equation for the reaction between propane and oxygen.

The overall energy change of this exothermic reaction is 2219 kJ/mol.

Table 4 shows the bond energies of the bonds in the reaction.

Calculate the bond energy of the C — H bond (X).

This question is about hydrogen and compounds of hydrogen. Figure 3 shows the displayed formulae for the reaction between hydrogen and chlorine.

Figure 3

Table 4 shows the bond energies.

Which expression shows how to calculate the overall energy change for the reaction in Figure 3 ? Use Table 4. Tick (✓) one box.

The reaction between hydrogen and chlorine is exothermic.

Explain why this reaction releases energy to the surroundings.

Figure 4 shows part of a reaction profile for the reaction between hydrogen and chlorine. Complete the reaction profile in Figure 4. You should:

• label the activation energy

• label the overall energy change.

Draw a dot and cross diagram for a molecule of hydrogen chloride (HC l). Show the outer shell electrons only.

Figure 5 represents molecules of methane and of poly(ethene).

Methane is a gas at room temperature but poly(ethene) is a solid at room temperature.

Explain why methane and poly(ethene) exist in different states at room temperature.

Sodium carbonate reacts with hydrochloric acid in an exothermic reaction.

The equation for the reaction is:

A student investigated the effect of changing the mass of sodium carbonate powder on the highest temperature reached by the reaction mixture.

Plan a method to investigate the effect of changing the mass of sodium carbonate powder on the highest temperature reached.

Figure 17 shows a line of best fit drawn through the student’s results.

Determine the gradient of the line of best fit in Figure 17.

Use the equation:

Give the unit.

The initial temperature of the reaction mixture is where the line of best fit would meet the y-axis.

Determine the initial temperature of the reaction mixture.

Show your working on Figure 17.

Another student repeated the investigation but added sodium carbonate until the sodium carbonate was in excess.

Which sketch graph shows the results obtained when sodium carbonate was added until in excess?

Tick (✓) one box.

Figure 18 shows a reaction profile for the reaction of sodium carbonate with hydrochloric acid.

What do labels X and Y represent on Figure 18 ?

How does the reaction profile show that the reaction is exothermic?

Use Figure 18.

Sodium carbonate reacts with hydrochloric acid in an exothermic reaction. The equation for the reaction is:

A student investigated the effect of changing the mass of sodium carbonate powder on the highest temperature reached by the reaction mixture.

Plan a method to investigate the effect of changing the mass of sodium carbonate powder on the highest temperature reached.

Figure 3 shows a line of best fit drawn through the student’s results.

Determine the gradient of the line of best fit in Figure 3. Use the equation:

Give the unit.

The initial temperature of the reaction mixture is where the line of best fit would meet the y-axis. Determine the initial temperature of the reaction mixture. Show your working on Figure 3.

Another student repeated the investigation but added sodium carbonate until the sodium carbonate was in excess. Which sketch graph shows the results obtained when sodium carbonate was added until in excess? Tick (✓) one box.

Figure 4 shows a reaction profile for the reaction of sodium carbonate with hydrochloric acid.

What do labels X and Y represent on Figure 4 ?

How does the reaction profile show that the reaction is exothermic? Use Figure 4.

A student investigated the reactivity of metals with hydrochloric acid.

This is the method used.

1. Measure 50 cm³ of hydrochloric acid into a polystyrene cup.

2. Measure the temperature of the hydrochloric acid.

3. Add one spatula of metal powder to the hydrochloric acid and stir.

4. Measure the highest temperature the mixture reaches.

5. Calculate the temperature increase for the reaction.

6. Repeat steps 1 to 5 three more times.

7. Repeat steps 1 to 6 with different metals.

Table 4 shows the student’s results.

Calculate the mean temperature increase X for magnesium in Table 4.

Do not include the anomalous result in your calculation.

Determine the order of reactivity for the metals cobalt, magnesium and zinc.

Use Table 4.

The range of measurements either side of the mean shows the uncertainty in the mean temperature increase.

Complete the sentence.

Use Table 4.

What type of variable is the volume of hydrochloric acid in this investigation?

Tick (✓) one box.

Suggest one way of improving step 3 in the method to give results which are more repeatable.

Figure 6 shows a reaction profile for the reaction of magnesium with hydrochloric acid.

What do labels A, B and C represent on Figure 6 ?

Choose answers from the box.

This question is about the reaction between hydrogen sulfide (H₂S) and oxygen. The equation for the reaction is:

What does H₂O(g) represent?

Calculate the volume of oxygen required to react with 50 cm³ of hydrogen sulfide.

Figure 6 shows part of the reaction profile for the reaction. The reaction is exothermic. Complete Figure 6. You should:

• complete the profile line

• label the activation energy

• label the overall energy change.

Figure 7 shows the displayed formula equation for the reaction of hydrogen sulfide with oxygen.

Figure 7

Table 5 shows some of the bond energies.

In the reaction the energy released forming new bonds is 1034 kJ/mol greater than the energy needed to break existing bonds. Calculate the bond energy X for the bond. Use Figure 7 and Table 5.

This question is about chemical reactions and energy. Hydrogen reacts with oxygen to produce water. This reaction releases energy.

Complete the word equation for the reaction. [1 mark hydrogen + oxygen → ____________

Figure 3 shows a reaction profile for the reaction between hydrogen and oxygen.

What do the labels W, X, Y and Z represent? Choose answers from the box.

The reaction between hydrogen and oxygen is used in a hydrogen fuel cell. What is the reason for using this reaction in a fuel cell? Tick (✓) one box.

A student investigated the voltage produced by a chemical cell. The student used different metals as the electrodes in the cell. The metals used were:

• copper

• iron

• magnesium.

Which two metal electrodes would produce the greatest voltage when used in the chemical cell? Give one reason for your answer.

This question is about displacement reactions.

The displacement reaction between aluminium and iron oxide has a high activation energy. What is meant by ‘activation energy’?

A mixture contains 1.00 kg of aluminium and 3.00 kg of iron oxide. The equation for the reaction is:

Show that aluminium is the limiting reactant. Relative atomic masses (A_r): O = 16 Al = 27 Fe = 56

Magnesium displaces zinc from zinc sulfate solution.

Complete the ionic equation for the reaction. You should include state symbols.

Explain why the reaction between magnesium atoms and zinc ions is both oxidation and reduction.

The reaction between hydrogen and oxygen releases energy.

A student drew a reaction profile for the reaction between hydrogen and oxygen. Figure 3 shows the student’s reaction profile.

The student made two errors when drawing the reaction profile. Describe the two errors.

The reaction between hydrogen and oxygen in a hydrogen fuel cell is used to produce electricity. Hydrogen fuel cells and rechargeable cells are used to power some cars. Give two advantages of using hydrogen fuel cells instead of using rechargeable cells to power cars.

Reactions occur at the positive electrode and at the negative electrode in a hydrogen fuel cell. Write a half equation for one of these reactions.

The three states of matter can be represented by a simple particle model. Figure 4 shows a simple particle model for hydrogen gas.

Give two limitations of this simple particle model for hydrogen gas.

The hydrogen gas needed to power a car for 400 km would occupy a large volume. Suggest one way that this volume can be reduced.

The energy needed for a car powered by a hydrogen fuel cell to travel 100 km is 58 megajoules (MJ). The energy released when 1 mole of hydrogen gas reacts with oxygen is 290 kJ The volume of 1 mole of a gas at room temperature and pressure is 24 dm³ Calculate the volume of hydrogen gas at room temperature and pressure needed for the car to travel 100 km

This question is about compounds of oxygen and hydrogen. Figure 2 represents the structure of hydrogen peroxide.

Figure 2

What is the correct formula of hydrogen peroxide? Tick (✓) one box.

Which type of bonding is shown in Figure 2 ? Tick (✓) one box.

Hydrogen peroxide decomposes in the presence of a catalyst. Which elements are often used as catalysts?

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Figure 3 shows the reaction profile for the decomposition of hydrogen peroxide. The word equation for this reaction is: hydrogen peroxide → water + oxygen

Labels A, B, C and D each represent a different part of the reaction profile. Use Figure 3 to answer Questions 02.4 and 02.5

Which label shows the activation energy? Tick (✓) one box.

Which label shows the energy of hydrogen peroxide? Tick (✓) one box.

The decomposition of hydrogen peroxide gives out energy to the surroundings. What type of reaction is this?

Tick (✓) one box.

Hydrogen and oxygen form water. A hydrogen atom contains one electron. An oxygen atom contains six electrons in the outer shell. Complete Figure 4 to show a dot and cross diagram for a water molecule. Show the outer electrons only.

This question is about ammonia, NH₃

Complete the dot and cross diagram for the ammonia molecule shown in Figure 6. Show only the electrons in the outer shell of each atom.

Give one limitation of using a dot and cross diagram to represent an ammonia molecule.

Explain why ammonia has a low boiling point. You should refer to structure and bonding in your answer.

Ammonia reacts with oxygen in the presence of a metal oxide catalyst to produce nitrogen and water.

Which metal oxide is most likely to be a catalyst for this reaction? Tick (✓) one box.

Figure 7 shows the displayed formula equation for the reaction.

Table 3 shows some bond energies.

Calculate the overall energy change for the reaction. Use Figure 7 and Table 3.

Explain why the reaction between ammonia and oxygen is exothermic. Use values from your calculation in Question 05.5

Figure 8 shows the reaction profile for the reaction between ammonia and oxygen. Complete Figure 8 by labelling the:

• activation energy

• overall energy change.

A student investigated the temperature change in displacement reactions between metals and copper sulfate solution.

This is the method used.

1. Measure 50 cm³ of the copper sulfate solution into a polystyrene cup.

2. Record the starting temperature of the copper sulfate solution.

3. Add the metal and stir the solution.

4. Record the highest temperature the mixture reaches.

5. Calculate the temperature increase for the reaction.

6. Repeat steps 1-5 with different metals.

Draw one line from each type of variable to the name of the variable in the investigation.

The student used a polystyrene cup and not a glass beaker.

Why did this make the investigation more accurate?

Tick one box.

Table 5 shows the student’s results.

Complete Figure 9.

Use data from Table 5.

The student concluded that the reactions between the metals and copper sulfate solution are endothermic.

Give one reason why this conclusion is not correct.

The temperature increase depends on the reactivity of the metal.

Write the metals magnesium, nickel and zinc in order of reactivity.

Use Table 5.

Y is an unknown metal.

Describe a method to find the position of Y in the reactivity series in Question 06.5

Figure 10 shows the reaction profile for the reaction between zinc and copper sulfate solution.

Which letter represents the products of the reaction?

Tick one box.

Which letter represents the activation energy?

Tick one box.

A student investigated the temperature change in displacement reactions between metals and copper sulfate solution. Table 2 shows the student’s results.

Plot the data from Table 2 on Figure 4 as a bar chart.

The student concluded that the reactions between the metals and copper sulfate solution are endothermic. Give one reason why this conclusion is not correct.

The temperature change depends on the reactivity of the metal. The student’s results are used to place copper, iron, magnesium and zinc in order of their reactivity. Describe a method to find the position of an unknown metal in this reactivity series. Your method should give valid results.

Draw a fully labelled reaction profile for the reaction between zinc and copper sulfate solution on Figure 5.