Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Unit
Physical Chemistry
442 practice questions
Topics covered
Practice questions
21–30 of 442
Question 21
3 marks · Easy
Answer and see the solution →(a)[1 mark]What does a negative value for ΔH indicate about a chemical reaction?
(b)[1 mark]Name one observable change you would expect in the surroundings during this reaction.
(c)[1 mark]Give an example, including a balanced equation with ΔH, for a type of reaction that has a negative enthalpy change.
Question 22
2 marks · Easy
Answer and see the solution →A reaction absorbs 45 kJ of heat energy when exactly 1.5 mol of the substance react completely. Calculate the enthalpy change, ΔH, for this reaction in kJ/mol. State your answer with the correct sign.
Question 23
2 marks · Easy
Answer and see the solution →Explain why energy must be supplied to the reactants in an endothermic reaction. Refer to the relative energies of reactants and products in your answer.
Question 24
3 marks · Easy
Answer and see the solution →The table shows the enthalpy changes for dissolving three different salts in water.
Enthalpy changes for dissolving salts in water Salt ΔH (kJ/mol) Potassium nitrate +34 Calcium chloride –81 Ammonium chloride +15 (a)[1 mark]Which salt dissolving is the most exothermic? Give a reason for your answer.
(b)[1 mark]Which salt dissolving is the most endothermic? State the value of ΔH for this salt.
(c)[1 mark]Explain what the positive sign of ΔH tells you about the dissolving process for ammonium chloride.
Question 25
1 mark · Easy
Answer and see the solution →Describe what you would feel if you held a container where an endothermic reaction is taking place.
Question 26
3 marks · Easy
Answer and see the solution →(a)[1 mark]Name the term that describes the total heat energy change during a chemical reaction.
(b)[2 marks]A chemical change absorbed 74 kJ when 2.0 mol of reactant were used. Calculate the enthalpy change, ΔH, in kJ/mol. Show your calculation.
Question 27
2 marks · Easy
Answer and see the solution →In a laboratory experiment, a reaction gave out 120 kJ of heat when 4.0 mol of the substance were used. Calculate the enthalpy change, ΔH, for this reaction in kJ/mol. Include the correct sign in your answer.
Question 28
4 marks · Normal
Answer and see the solution →Hydrated copper(II) sulfate is dissolved in water in a polystyrene cup. The temperature drops from 22.5 °C to 18.0 °C.
(a)[2 marks]State whether this reaction is endothermic or exothermic and explain how you know.
(b)[1 mark]Calculate the temperature change for this reaction.
(c)[1 mark]Suggest how the enthalpy change () of this reaction could be calculated, naming any values that would be needed.
Question 29
3 marks · Normal
Answer and see the solution →When 0.015 mol of ammonium nitrate (NH₄NO₃) dissolves in 40.0 g of water, the temperature falls by 5.8 °C. The specific heat capacity of water is 4.18 J g⁻¹ °C⁻¹.
Calculate the enthalpy change, ΔH, for the dissolution of ammonium nitrate in kJ/mol. Give your answer to two decimal places.
Question 30
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.