Print this chapterPrint this chapter

Module 4 Intro

1. Module 4 Intro

1.15. Page 4

Lesson 2

Module 4—Properties of Solutions

Watch and Listen

 

In the following videos, you will see how dramatic endothermic and exothermic reactions can be!


Endothermic



Exothermic



 

Self-Check

 

A drawing of a pouch that is labelled as a Heat Pack. Part of the diagram shows the organization of the contents inside the pack. An inner pouch containing water is surrounded on all sides by solid calcium chloride.

Similar to the cold pack mentioned earlier, a heat pack contains two compartments: a large outer pouch containing calcium chloride, and water stored in the hollow inner cavity. A heat pack is used by breaking the pouch containing the calcium chloride crystals, allowing them to come into contact with water and dissolve.

 

SC 7. Write the balanced chemical equations for the changes that occur when calcium chloride dissolves in the water in the hot pack.

 

SC 8. Explain the type of energy changes involved in the hot pack during its operation.


Check your work.
Self-Check Answers

 

SC 7.  CaCl2(s) → Ca2+(aq)  +  2 Cl-(aq)

 

SC 8.  Many energy changes are involved:

  • The calcium chloride dissociates, separating the calcium ions from the chloride ions. This is an endothermic process, which absorbs energy.

  • The formation of bonds between water and the ions is very exothermic, releasing a lot of energy.

  • The overall result is that far more energy comes out of calcium chloride than is absorbed. The overall process is exothermic, and the water heats up.