Lesson 2

Chemical Reactions Creating or Using Heat Energy

Seventh Example

Here (to the left) we have one test tube with some water in it and then another test tube (in the rack) with some solid ammonium nitrate in it. The amounts are specified in your workbook in Exercise 4. The thermometer is used to get the temperature of the water. (The reason we have you use 3 ml of water is to make sure you have enough to cover the bulb of the thermometer.) Note the temperature. (you may not be able to make it out here, but you will in the lab.) After the ammonium nitrate from the other test tube has been poured into the water (to the right), the thermometer is used to gently mix the solid and the liquid. The solid ammonium nitrate dissolves and as it does so the temperature goes down.

Comments

With some chemical reactions, heat is given off during the reaction and the temperature goes up. In this particular one, heat is used up; therefore, the temperature goes down.

Now, or when you are in the lab, do this exercise so that you can see the temperature change first hand and, of course, clean up your glassware.