Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Chapter
Energetics
117 practice questions
Topics covered
- Exothermic reactions19 practice questions
- Endothermic reactions19 practice questions
- Measuring enthalpy changes of reactions19 practice questions
- Calorimetry experiments for determining the enthalpy changes of reactions18 practice questions
- Why do reactions either give out or absorb heat?19 practice questions
- Calculation of enthalpy changes of reaction using bond energies19 practice questions
Practice questions
11–20 of 48 · Normal
Question 11
4 marks · Normal
Answer and see the solution →The table below shows the temperature change when different masses of potassium chloride (KCl) are dissolved in 100 g of water.
Temperature changes for dissolving KCl Mass of KCl (g) Temperature change (°C) 1.0 0.7 2.0 1.5 3.0 2.3 4.0 3.2 (Specific heat capacity of water = 4.18 J g⁻¹ °C⁻¹)
(a)[1 mark]Describe the pattern shown by the data in the table.
(b)[1 mark]Calculate the heat absorbed by the solution when 4.0 g of KCl is dissolved.
(c)[2 marks]Potassium chloride has a molar mass of 74.6 g/mol. Calculate the enthalpy change (ΔH) for dissolving KCl in kJ/mol for the entry with 4.0 g dissolved.
Question 12
1 mark · Normal
Answer and check →Which expression is used to calculate the enthalpy change of a reaction per mole?
- A.ΔH = q × n
- B.ΔH = q / n
- C.ΔH = n / q
- D.ΔH = q + n
Question 13
4 marks · Normal
Answer and see the solution →A student dissolves 1.5 g of sodium carbonate (Na₂CO₃, molar mass = 106 g/mol) in 50 g of water in a polystyrene cup. The temperature rises by 1.8 °C. The specific heat capacity of water is 4.18 J g⁻¹ °C⁻¹.
(a)[1 mark]Calculate the heat energy transferred to the solution (q).
(b)[1 mark]Calculate the number of moles of Na₂CO₃ dissolved.
(c)[2 marks]Calculate the enthalpy change, ΔH, for dissolving Na₂CO₃ in kJ/mol. Give your answer to two decimal places.
Question 14
2 marks · Normal
Answer and see the solution →When 0.10 mol of solid ammonium nitrate, , dissolves in water, the temperature of the water decreases as 3.40 kJ of heat is absorbed from the surroundings.
Calculate the molar enthalpy change, , for the dissolution of ammonium nitrate in kJ/mol. Include the correct sign.
Question 15
3 marks · Normal
Answer and see the solution →A reaction takes place in which 2.5 g of calcium chloride, , dissolves in water and releases 8.6 kJ of heat to the surroundings.
Show how you would calculate the molar enthalpy change, , for this process. Give your answer in kJ/mol and include the correct sign. Explain each step in your calculation.
Question 16
2 marks · Normal
Answer and see the solution →A reaction absorbs 150 kJ of heat energy when exactly 3.0 mol of the reactant react completely.
Calculate the enthalpy change, ΔH, for this reaction in kJ/mol.
Show your working. Include the correct sign.
Question 17
2 marks · Normal
Answer and see the solution →A student adds dilute hydrochloric acid to sodium hydroxide in a polystyrene cup. The temperature of the mixture rises.
State the name of this type of experimental method, and state the reason a polystyrene cup is used.
Question 18
4 marks · Normal
Answer and see the solution →A student investigates the enthalpy change when magnesium reacts with dilute sulfuric acid in a calorimeter.
(a)[1 mark]State the measurements the student should take during the experiment.
(b)[1 mark]Explain why it is important to stir the mixture before taking the final temperature reading.
(c)[1 mark]Suggest one reason the measured enthalpy change might be lower than the actual value.
(d)[1 mark]Describe how the student could improve the accuracy of this experiment.
Question 19
3 marks · Normal
Answer and see the solution →In a calorimetry experiment, 1.2 g of magnesium reacts with 100 cm³ of dilute hydrochloric acid. The temperature of the solution rises by 9.0 °C. Assume the specific heat capacity of water is 4.18 J/g°C and the density of the solution is 1.00 g/cm³.
Calculate the heat evolved in the reaction. Give your answer in kJ (kilojoules).
Question 20
3 marks · Normal
Answer and see the solution →When measuring the enthalpy change of a reaction between zinc and copper(II) sulfate solution in a calorimeter, a student notices bubbles forming.
Explain why bubbles might affect the temperature readings in this experiment. Suggest two ways the experiment could be improved to obtain more accurate results.