The method and the results are on the exothermic endothermic lab. Do the analysis yourself first, then check the answers below.
Quick answer: An exothermic reaction releases energy to its surroundings, so the temperature rises, as in a hand warmer or a burning candle. These answers go with the grade 8 science lab on exothermic endothermic: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
Model answers use the sample data. Your own values will differ a little, but the signs of the changes should agree. Check your calculations by redoing them with your own numbers.
Calcium chloride is exothermic. Ammonium chloride and potassium nitrate are endothermic. Sodium chloride changed by only 0.5 °C, so it is hard to classify.
The change is −0.5 °C, which equals the smallest division of the thermometer. It could be a reading error, so it is within the uncertainty.
Question 5 Heat loss
Polystyrene is a poor conductor and the lid cuts heat exchange with the air. Without them the water would gain or lose energy from the room, so the measured ΔT would be smaller than the true value.
Question 6 Choosing solids for packs
Calcium chloride suits a hot pack, as it warms the water by 9.5 °C, and potassium nitrate suits a cold pack, as it cools by 7.0 °C. A concern is that calcium chloride irritates skin and eyes.
Question 7 Improving reliability
Repeat each test three times and take the mean. Use the same number of moles, or the same mass, in each test, and use a thermometer with finer divisions. Repeats and finer scale improve reliability.
