Exothermic & endothermic reactions

A student investigated an exothermic reaction.

The student reacted solid calcium oxide with water to produce calcium hydroxide.

What is meant by an ‘exothermic’ reaction?

The formula of calcium hydroxide is Ca(OH)₂

Calculate the percentage by mass of oxygen in calcium hydroxide.

Relative atomic mass (A_r): O = 16

Relative formula mass (M_r): Ca(OH)₂ = 74

When solid calcium oxide is added to water, the temperature of the reaction mixture changes.

Plan a method to investigate how changing the mass of calcium oxide affects the temperature change of the reaction mixture.

A student investigated an exothermic reaction.

The student reacted solid calcium oxide with water to produce calcium hydroxide.

What is meant by an ‘exothermic’ reaction?

The formula of calcium hydroxide is Ca(OH)₂

Calculate the percentage by mass of oxygen in calcium hydroxide.

Relative atomic mass (A_r): O = 16

Relative formula mass (M_r): Ca(OH)₂ = 74

When solid calcium oxide is added to water, the temperature of the reaction mixture changes.

Plan a method to investigate how changing the mass of calcium oxide affects the temperature change of the reaction mixture.

A student investigated the temperature change when different masses of zinc were added to copper sulfate solution.

Figure 5 shows the apparatus.

This is the method used.

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

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

3. Add 1.0 g of zinc.

4. Stir the mixture.

5. Measure the highest temperature reached.

6. Repeat steps 1 to 5 two more times.

7. Repeat steps 1 to 6 with different masses of zinc.

The student varied the mass of zinc.

What type of variable is the mass of zinc?

Tick () one box.

The word equation for the reaction is:

zinc + copper sulfate → salt A + copper

What is the name of salt A ?

The temperature of the solution increases when zinc reacts with copper sulfate solution.

Give two other observations that can be made when zinc reacts with copper sulfate solution.

Figure 6 shows the highest temperature reached in one experiment.

Complete Table 3.

Use Figure 6.

A teacher repeated the investigation using a digital thermometer.

Table 4 shows the results.

Calculate value B in Table 4.

The range of the results is the minimum value of temperature increase to the maximum value of temperature increase.

What is the range of temperature increase for the experiment with 2.0 g of zinc?

One of the results for 3.0 g of zinc is anomalous.

Which result is anomalous?

Suggest one reason why this result is anomalous.

Nitric acid (HNO₃) is a strong acid.

What is meant by a ‘strong acid’?

Nitric acid is used as a dilute aqueous solution.

What is meant by ‘dilute aqueous solution’?

10 cm³ of a nitric acid solution has a pH of 1

Water is added to the nitric acid solution to change the pH of the nitric acid solution to pH 3

How does the hydrogen ion concentration change?

Tick () one box.

Write the ionic equation for the reaction between an acid and an alkali.

The equation shows the reaction between magnesium carbonate and nitric acid.

What is the ratio of the number of moles of magnesium carbonate to the number of moles of nitric acid in the reaction?

Tick () one box.

A student mixed some magnesium carbonate with excess nitric acid.

The student then added two drops of universal indicator to the solution.

What colour was the solution after the addition of universal indicator?

Tick () one box.

A student investigated the temperature change when different masses of

magnesium carbonate were reacted with excess nitric acid.

Figure 6 shows the apparatus.

This is the method used.

1. Pour 50 cm³ of nitric acid into a polystyrene cup.

2. Measure the temperature of the solution.

3. Add 0.50 g of magnesium carbonate.

4. Stir the mixture.

5. Measure the temperature.

6. Repeat steps 1 to 5 with different masses of magnesium carbonate.

Give two improvements to the method to produce more accurate results.

Do not refer to improvements to the apparatus in your answer.

A student investigated the temperature change when magnesium was added to zinc sulfate solution. Figure 5 shows the apparatus.

Which piece of equipment is labelled X ? Tick (✓) one box.

Which piece of equipment is the best to use to measure volumes of solution? Tick (✓) one box.

The student added 1.0 g of magnesium to 50 cm³ of zinc sulfate solution and

measured the temperature increase. The student repeated the experiment two more times. Table 1 shows the results.

Calculate value Y in Table 1.

The student then added 1.2 g of magnesium to 50 cm³ of zinc sulfate solution. The temperature increased by 9.0 °C. Calculate the temperature increase when the student adds 0.40 g of magnesium to 50 cm³ of zinc sulfate solution.

What is the name given to a reaction which causes the temperature to increase? Tick (✓) one box.

The student repeated the experiment with 1.2 g of copper and 50 cm³ of zinc sulfate solution. The temperature did not increase. Give one reason why.

This question is about hydrogen chloride and sodium hydroxide.

A chlorine atom has 7 electrons in the outer shell. A hydrogen atom has 1 electron in the outer shell. Figure 4 represents part of a dot and cross diagram for a molecule of hydrogen chloride.

Complete the dot and cross diagram. Use dots (ο) and crosses (x) to represent electrons. You should show only the electrons in the outer shells.

Hydrogen chloride dissolves in water to produce hydrochloric acid. Hydrochloric acid reacts with sodium hydroxide solution. Complete the word equation for the reaction between hydrochloric acid and sodium hydroxide.

hydrochloric acid + sodium hydroxide → + water

Solutions of hydrochloric acid and sodium hydroxide are reacted and the temperature change is recorded.

In the reaction, 3.65 g of hydrogen chloride reacts with 4.00 g of sodium hydroxide. 1.80 g of water is produced. Calculate the mass of the other product.

Figure 5 shows part of the thermometer used to measure the temperature.

What is the temperature reading on the thermometer?

In the reaction, the temperature increases. What type of reaction is happening when the temperature increases?

Sodium hydroxide is an alkali. Which two ions are in sodium hydroxide solution? Tick (✓) two boxes.

Plan an investigation to find the order of reactivity of three metals. You should use the temperature change when each metal reacts with hydrochloric acid.

A student investigated the change in temperature when different masses of zinc were added to copper sulfate solution. This is the method used.

1. Measure the volume of copper sulfate solution using a measuring cylinder.

2. Pour the copper sulfate solution into a metal container.

3. Add 2 g of zinc.

4. Measure the temperature of the solution.

5. Repeat steps 1 to 4 with different masses of zinc.

Figure 7 shows the apparatus.

Give three improvements to the investigation to make the results more accurate.

Figure 8 shows part of the measuring cylinder.

What is the volume of copper sulfate solution in Figure 8 ?

When zinc was added to copper sulfate solution the temperature increased. Figure 9 shows the reaction profile.

What type of reaction is shown in Figure 9 ? Tick (✓) one box.

Figure 10 shows the results.

Determine the gradient of the line in Figure 10. Use the equation:

Suggest why the student should not use more than 10 g of zinc. Use Figure 10. You should extend the graph line.

This question is about energy change. A student investigated the temperature change when 10 g of ammonium nitrate was

This is the method used.

1. Measure the temperature of 100 cm³ of water.

2. Add 10 g of ammonium nitrate.

3. Stir once.

4. Measure the temperature of the solution every minute for 7 minutes.

Figure 3 shows the apparatus.

What is the dependent variable in this investigation?

Give three improvements to the investigation to make the results more accurate.

Figure 4 shows the results.

Explain the results.

Draw a reaction profile for an exothermic reaction. You should label:

• the energy level of the reactants and of the products

• the activation energy

• the overall energy change.

A student investigated the temperature change when metal X was added to copper sulfate solution. This is the method used.

1. Add 25 cm³ of copper sulfate solution to a beaker.

2. Measure the temperature of the copper sulfate solution.

3. Add 1.0 g of metal X and stir.

4. Measure the highest temperature reached when metal X is added to copper sulfate solution.

5. Repeat steps 1 to 4 with different metals.

Figure 1 shows the apparatus used.

Figure 2 shows the thermometer reading of the copper sulfate solution at the start of the investigation.

The highest temperature reached when metal X was added to copper sulfate solution was 35.5 °C Determine the temperature change when metal X is added to copper sulfate solution. Use Figure 2. Highest temperature = 35.5 °C

Give two variables the student should keep the same in this investigation.

The student repeated the experiment with metal Y. Table 1 shows four results for metal Y.

Calculate the mean temperature change for metal Y. Do not include the anomalous result in your calculation.

The more reactive the metal added to copper sulfate solution, the greater the temperature change. Figure 3 shows a reactivity series.

Figure 3

Calcium Magnesium Zinc Copper Silver least reactive

The student repeated the experiment. The student added:

• magnesium to copper sulfate solution

• an unknown metal A to copper sulfate solution.

Table 2 shows the results.

The student concludes metal A is zinc. Give one reason why the student is correct. Use Figure 3 and Table 2.

The student did the experiment with silver and copper sulfate solution. What happens to the temperature of the mixture? Use Figure 3. Tick (✓) one box.

Suggest one reason why the student should not add potassium metal to copper sulfate solution.

100 cm³ of the copper sulfate solution contains 1.8 g of copper sulfate. Calculate the mass of copper sulfate in 25 cm³ of this copper sulfate solution.

A student investigated the temperature change when magnesium was added to copper sulfate solution. This is the method used.

1. Pour 30 cm³ of copper sulfate solution into a polystyrene cup.

2. Measure the temperature of copper sulfate solution every minute for 3 minutes.

3. Add magnesium on the fourth minute.

4. Measure the temperature of the mixture at 5 minutes and then every minute up to 14 minutes.

What is the dependent variable in this investigation?

The student used the results to plot a graph.

Figure 4 shows the graph.

Suggest why the copper sulfate solution was left for four minutes before adding the magnesium.

Complete Figure 4 by:

• drawing a line of best fit through all the points after 7 minutes

• extending the line back to 4 minutes.

The temperature change for the reaction is the temperature difference between the two graph lines at 4 minutes. Determine the temperature change for the reaction. Use Figure 4.

Explain why the temperature of the mixture decreases after 7 minutes.

The student repeated the experiment with an unknown metal Q instead of magnesium. All the other variables were kept the same. The student recorded a smaller temperature change. Suggest the identity of metal Q. Give one reason for your answer.

A copper sulfate solution contained 0.100 moles of copper sulfate dissolved

Calculate the mass of copper sulfate in 30.0 cm³ of this solution. Relative formula mass (M_r): CuSO₄ = 159.5

This question is about energy changes.

Which of these items uses an endothermic reaction? Tick (✓) one box.

Figure 1 shows the reaction profile for an exothermic reaction.

Which letter represents the activation energy for the reaction? Tick (✓) one box.

Which letter represents the overall energy change for the reaction? Tick (✓) one box.

Complete the sentence. Choose the answer from the box.

In an exothermic reaction the energy of the products is the energy of the reactants.

A student measured the temperature at the start and at the end of a reaction. Name the apparatus used to measure the temperature.

Figure 2 shows the temperature at the end of the reaction.

Complete Table 1. Use Figure 2.

This question is about salts. Ammonium nitrate solution is produced when ammonia gas reacts with nitric acid.

Give the state symbol for ammonium nitrate solution.

What is the formula of nitric acid? Tick (✓) one box.

Ammonia gas dissolves in water to produce ammonia solution. Ammonia solution contains hydroxide ions, OH^– A student adds universal indicator to solutions of nitric acid and ammonia. What colour is observed in each solution?

Colour in nitric acid Colour in ammonia solution

The student gradually added nitric acid to ammonia solution. Which row, A, B, C or D, shows the change in pH as the nitric acid is

Calculate the percentage by mass of oxygen in ammonium nitrate (NH₄NO₃). Relative atomic masses (A_r): H = 1 N = 14 O = 16 Relative formula mass (M_r): NH₄NO₃ = 80

Describe a method to investigate how the temperature changes when different masses of ammonium nitrate are dissolved in water. You do not need to write about safety precautions.

This question is about salts. Ammonium nitrate solution is produced when ammonia gas reacts with nitric acid.

Give the state symbol for ammonium nitrate solution.

What is the formula of nitric acid? Tick (✓) one box.

Ammonia gas dissolves in water to produce ammonia solution. Ammonia solution contains hydroxide ions, OH^– A student adds universal indicator to solutions of nitric acid and ammonia. What colour is observed in each solution?

Colour in nitric acid Colour in ammonia solution

The student gradually added nitric acid to ammonia solution. Which row, A, B, C or D, shows the change in pH as the nitric acid is

Calculate the percentage by mass of oxygen in ammonium nitrate (NH₄NO₃). Relative atomic masses (A_r): H = 1 N = 14 O = 16 Relative formula mass (M_r): NH₄NO₃ = 80

Describe a method to investigate how the temperature changes when different masses of ammonium nitrate are dissolved in water. You do not need to write about safety precautions.

This question is about the elements in Group 2 of the periodic table.

Figure 9 shows the positions of four elements, A, B, C, and D, in the periodic table.

Which element is in Group 2? Tick one box.

Group 2 metal carbonates break down when heated to produce a metal oxide and a gas. metal carbonate metal oxide + gas

Name the two products when calcium carbonate (CaCO₃) is heated.

What type of reaction happens when a compound breaks down? Tick one box.

The metal carbonate takes in energy from the surroundings to break down. What type of reaction takes in energy from the surroundings? Tick one box.

Figure 10 shows the volume of gas produced when a Group 2 metal carbonate is heated.

The student collected 5.2 dm³ of gas. What mass of the Group 2 metal carbonate is heated?

Calculate the mass of the Group 2 carbonate needed to produce 24 dm³ of gas. Use your answer from question 04.5 to help you.

A student heated different masses of a Group 2 carbonate. The student measured the volume of gas produced. Figure 11 shows a graph of the student’s results. The student calculates the gradient of the line in Figure 11 The student makes two mistakes.

Identify the two mistakes the student makes. Calculate the correct gradient of the line.

A student repeated the experiment with a different Group 2 metal carbonate (XCO₃). The relative formula mass (M_r) of XCO₃ is 84 Relative atomic masses (A_r): C = 12 O = 16 Calculate the relative atomic mass (A_r) of X. Name metal X. Use the periodic table.

Group 2 metal carbonates thermally decompose to produce a metal oxide and a gas.

Give the formula of each product when calcium carbonate (CaCO₃) is heated.

The relative formula mass (M_r) of a Group 2 metal carbonate is 197 Relative atomic masses (A_r): C = 12 O = 16 Calculate the relative atomic mass (A_r) of the Group 2 metal in the metal carbonate. Name the Group 2 metal.

Figure 8 shows the volume of gas produced when a different Group 2 carbonate, W, is heated.

Calculate the gradient of the line in Figure 8 Give the unit.

24 dm³ of gas is produced when one mole of a Group 2 carbonate is heated. Determine the relative formula mass of the Group 2 carbonate W. Use Figure 8