The questions are on the exothermic endothermic test. Take it under real conditions before reading the mark scheme.
Quick answer: An exothermic reaction releases energy to its surroundings, so the temperature rises, as in a hand warmer or a burning candle. This mark scheme gives the model answers and the marks for the 8 questions of the grade 8 science test on exothermic endothermic, from definitions to correct the idea, with the equivalent answers to accept.
Marks are in each model answer. Accept equivalent wording, and give error-carried-forward credit where a later part uses a wrong earlier value correctly.
Level: Grade 8 science (Year 9 · Class 8) · Curriculum: MS-PS1-6
Question 1 Definitions (2 marks)
- A reaction or process that absorbs energy from the surroundings, so the temperature falls.
- An instant cold pack (or melting ice, or photosynthesis).
Marking: 1 mark each.
Question 2 Classify (2 marks)
- Exothermic.
- Endothermic.
Marking: 1 mark each.
Question 3 Temperature change (3 marks)
- 27.0 − 18.5 = +8.5 °C.
- It is exothermic, because the temperature rose, so energy was released to the surroundings.
Marking: 1 mark for ΔT; 1 for exothermic; 1 for reason.
Question 4 Energy calculation (3 marks)
- Q = 80 × 4.2 × 7.5 = 2520 J.
- ΔT = 2520 ÷ (160 × 4.2) = 3.75 °C.
Marking: 1 mark for substitution, 1 for 2520 J; 1 for 3.75 °C.
Question 5 Cold pack graph (3 marks)
- 5 °C.
- 22 − 5 = 17 °C.
- The warmer room transfers energy to the pack, so it warms back up.
Marking: 1 mark each.
Question 6 How a hand warmer works (3 marks)
- Iron reacts with oxygen from the air in an exothermic reaction, which releases energy as heat. The pack stays warm while iron remains. It stops when the iron is used up, and then it cools.
Marking: 1 mark exothermic reaction with oxygen; 1 mark energy released as heat; 1 mark stops when iron used up.
Question 7 Energy diagram (2 marks)
- Exothermic, since products are lower.
- 150 − 110 = 40 kJ released.
Marking: 1 mark each.
Question 8 Correct the idea (2 marks)
- The pack absorbs energy as its solid dissolves. Energy flows from the warm knee into the colder pack, so the knee cools.
Marking: 1 mark for energy absorbed by the pack; 1 mark for direction from knee to pack.
