A materials laboratory tests self-heating meal packs for an emergency food box. Fig. 1 shows a sealed pack containing water and calcium oxide separated by a...
Question 1 Report
A materials laboratory tests self-heating meal packs for an emergency food box. Fig. 1 shows a sealed pack containing water and calcium oxide separated by a thin barrier. When the barrier is broken, the substances mix and the pack warms a meal container. The table shows results from packs containing different masses of calcium oxide. Each pack contains 80 g of water initially at 16.0 degrees C.
| mass of calcium oxide / g | maximum temperature of water / degrees C |
|---|---|
| 5.0 | 28.5 |
| 10.0 | 39.0 |
| 15.0 | 47.2 |
(a) State the temperature rise for the pack containing 10.0 g of calcium oxide. [1]
(b) Give the name of the type of energy change shown by these results. [1]
(c) Use the table to suggest why a manufacturer should not simply use 30.0 g of calcium oxide in every pack. [2]
(d) Give one safety precaution needed when filling the packs with calcium oxide. [1]
Answer Details
(a)
\[39.0-16.0=23.0\text{ degrees C}\]
The temperature rise is 23.0 degrees C. [1]
(b) This is an exothermic energy change, or exothermic reaction. [1]
(c) The table shows that a larger mass of calcium oxide produces a greater temperature rise. Using 30.0 g could therefore make the pack dangerously hot, damage the meal container, or burn the user. [2]
(d) One suitable precaution is to wear eye protection, wear gloves, or avoid contact with water when filling the packs. [1]
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