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Which of these reactants cause an exothermic chemical reaction when combined with water? Select all correct answers. (Hint: Refer to the Key Terms tab above the graph)

Ammonium chloride

Calcium chloride

Magnesium chloride

Magnesium sulfate

Sodium acetate
4
Of the reactants you selected in Question 3, which one produces the most exothermic reaction when combined water? Briefly justify your answer.

5
Instant cold packs, like those used to treat injuries, start working when water mixes with ammonium chloride.

To design a pack that gets even colder, what temperature change must occur?

A
A decrease in temperature of less than 2°C

B
An increase in temperature of at least 23 °C

C
A decrease in temperature of more than 7 °C

D
An increase in temperature of less than 3 °C

1 answer

Question 3: Reactants that cause an exothermic reaction when combined with water

The correct answers are:

  • Calcium chloride
  • Magnesium chloride

Justification: Calcium chloride and magnesium chloride are known to release heat when they dissolve in water, indicating that they cause exothermic reactions. Ammonium chloride, on the other hand, absorbs heat when dissolved, leading to an endothermic reaction.

Question 4: Most exothermic reaction

The reactant that produces the most exothermic reaction when combined with water is:

  • Calcium chloride

Justification: Calcium chloride has a higher capacity to release energy as heat when dissolving in water compared to other common salts. Its dissolution results in a greater temperature increase in the surrounding solution than that produced by magnesium chloride or other listed compounds.

Question 5: Temperature change for a colder instant cold pack

Correct answer:

  • C: A decrease in temperature of more than 7 °C

Justification: To create a cold pack that gets even colder, the temperature must decrease significantly. A decrease of more than 7 °C is necessary to achieve a noticeably colder effect for treating injuries, which aligns with typical temperature reductions seen in effective instant cold packs.