Quick answer: An exothermic reaction releases energy to the surroundings and its temperature rises; an endothermic reaction absorbs energy and its temperature falls. This Chemistry 9-10 test on energy changes has 8 questions worth 20 marks, to do in 45 minutes: hand warmers and cold packs, reading a reaction profile and hydrogen fluoride. The mark scheme is on a separate page; free printable PDF.
This chemistry grades 9-10 test on energy changes test works like a real class test. The mark scheme is on a separate page, so revise with the lesson first.
This test lasts 45 minutes and is worth 20 marks. Answer every question. Show each step of a calculation, give units, and write the sign of ΔH. The atomic masses and bond energies you need are given in the questions.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS1-4
Energy changes test: the test questions
Question 1 Hand warmers and cold packs (2 marks)
A hand warmer becomes hot and an instant cold pack becomes cold.- State which reaction is exothermic. (1 mark)
- State what happens to the temperature of the surroundings in an endothermic reaction. (1 mark)
Question 2 Reading a reaction profile (3 marks)
The figure shows the profile for a reaction.- Name the energy shown by arrow X. (1 mark)
- State the sign of the energy change shown by arrow Z. (1 mark)
- State whether the reaction is exothermic or endothermic. (1 mark)
Question 3 Hydrogen fluoride (3 marks)
H₂ + F₂ → 2HF. Bond energies: H–H 436, F–F 158, H–F 568 kJ/mol.- Calculate the energy needed to break the bonds. (1 mark)
- Calculate the energy released when the bonds form. (1 mark)
- Calculate ΔH. (1 mark)
Question 4 Energy from a temperature rise (3 marks)
A reaction in 200 g of water raises its temperature by 8.5 °C (c = 4.2 J/g/°C). The reaction used 0.050 mol of reactant.- Calculate the energy transferred in kJ. (2 marks)
- Calculate ΔH in kJ/mol. (1 mark)
Question 5 Starting a fire (2 marks)
Wood burns exothermically, yet it does not catch fire by itself in air. Explain why a flame must first be applied. (2 marks)Question 6 Bond breaking (2 marks)
Explain why breaking bonds is endothermic and making bonds is exothermic. (2 marks)Question 7 Self-heating can (3 marks)
A self-heating can of soup contains calcium oxide and water: CaO + H₂O → Ca(OH)₂.- State whether the reaction is exothermic or endothermic. (1 mark)
- Describe where the products lie compared with the reactants on a reaction profile. (1 mark)
- Explain how it heats the soup. (1 mark)
Question 8 Energy per mole (2 marks)
A fuel releases 125 kJ when 0.25 mol burns. Calculate ΔH per mole, including the sign. (2 marks)
