chemistryTopic 5 · Energy ChangesPaper 1Grades 8–9
Which hand-warmer design is safest and most effective?
Starting scenario
Pack A raises 100 g water by 18 °C in 90 s and can be reused after heating. Pack B raises it by 27 °C in 45 s but sometimes reaches 72 °C at the skin. Both contain the same mass of reacting material; the cup loses heat to the room.
You will work through 8 staged questions that build up the science you need. Then you will answer one big-picture question from memory, with no checklist to help you — and only afterwards will the full connection map be revealed.