Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Section
Endothermic reactions
19 practice questions
Practice questions
11–19 of 19
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 · Hard
Answer and see the solution →When 3.5 mol of substance X react with an acid, the reaction absorbs 96 kJ of heat energy from the surroundings.
Calculate the enthalpy change, , for this reaction in kJ/mol. State whether it is endothermic or exothermic.
Question 18
5 marks · Hard
Answer and see the solution →A student mixed 6.0 g of potassium nitrate (KNO₃, molar mass = 101 g/mol) in 50.0 g of water in a calorimeter. The temperature of the water fell by 3.2 °C. The specific heat capacity of water is 4.18 J g⁻¹ °C⁻¹.
(a)[2 marks]Calculate the number of moles of KNO₃ dissolved. (2 marks)
(b)[2 marks]Calculate the amount of heat (q, in J) absorbed by the water during the dissolving process. (2 marks)
(c)[1 mark]Calculate the enthalpy change, ΔH, for dissolving KNO₃ in kJ/mol. (1 mark)
Question 19
2 marks · Hard
Answer and see the solution →A reaction releases 212 kJ of heat when 7.0 mol of a reactant are completely used up. Calculate the enthalpy change, , in kJ/mol for this reaction. State the sign of and what it shows about the direction of energy transfer.