Feel the Heat Answer Key

Vocabulary: calorimeter, conductor, controlled experiment, dissolve, endothermic, exothermic,

insulator, solute, solution, solvent, surroundings, system

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

[Note: The purpose of these questions is to activate prior knowledge and get students thinking.

Students are not expected to know the answers to the Prior Knowledge Questions.]

Eduardo hurts his knee during a basketball game. The trainer applies a cold pack, which gets

cold after being squeezed. The next day, Eduardo’s friend Beth is going sledding. Beth buys

some hand warmers and puts them into her gloves. All morning, her hands stay toasty warm.

1. How do you think these devices work?

Answers will vary. [Cold packs typically work by dissolving a salt such as ammonium nitrate

into water. Commercial hot packs work by crystalizing sodium acetate or by oxidizing iron.]

2. Where do you think the “cold” and the heat comes from?

Answers will vary.

Gizmo Warm-up

As you saw with the instant cold pack and the hand warmers, some

reactions absorb energy while others release it. In the Feel the Heat

Gizmo, you will explore these energy changes while making your own

hot and cold packs.

To begin, select the TEST POWDERS tab. Drag a bottle of NaC2H3O2

(sodium acetate) from the shelf. Using the sliders, decide how much

water and powder to add. Note the beginning temperature, and then

press Play ( ) to see what happens.

1. Did the temperature go up or down? Up

2. Experiment with different powders until you find one that produces the opposite effect.

What powder did you use? NH4NO3, KCl, and NaCl will produce a temperature decrease.

When a powder dissolves in water a solution is formed. The powder is the solute and the

water is the solvent. Oftentimes energy changes accompany the formation of a solution. When

added to water, some powders cause the resulting solution to get hot, while others make it cold.

Some powders don’t produce a temperature change at all. When energy changes do occur,

they can be put to good use.