Question

physical and chemical changes - 7.6c
10
meals ready - to - eat (mres) are packaged meals that include their own disposable heat pack to warm the food. students are challenged to duplicate the disposable heat packs found in the mres in the science classroom using chemical reactions. the final product must be safe, heat the food, and be light in mass.

chemical reaction	thermal energy	amount required to produce reaction	substance produced
2	released	5 g	water
3	absorbed	10 g	water
4	released	3 g	toxic gas

based on the observations, which chemical reaction would be the best choice for making a heat pack? enter your answer in the space below.

Explanation:

Step1: Identify requirements

The heat - pack must be safe, heat the food, and be light in mass.

Step2: Evaluate reaction 1

Reaction 1 requires 100 kg of substance, which is heavy, so it's not a good choice.

Step3: Evaluate reaction 2

Reaction 2 releases thermal energy, requires only 5 g of substance, and produces water (safe), so it meets the requirements.

Step4: Evaluate reaction 3

Reaction 3 absorbs thermal energy, so it cannot be used to heat food.

Step5: Evaluate reaction 4

Reaction 4 produces a toxic gas, so it is not safe.

Answer:

2