Question

activity a: observing chemical changes
get the gizmo ready:

• click reset ( 2 ). check that the reactants are still sodium and water.
• turn on the label reactants checkbox.

introduction: it is important to distinguish chemical changes, in which new substances are formed, from physical changes, which do not create new substances. in this activity, you will look at many kinds of evidence that chemists use to see if a chemical change has taken place?
question: what kinds of evidence indicate a chemical change has taken place?

1. observe: some chemical reactions release heat, and others absorb heat. in an exothermic reaction, heat is released and the temperature of the system rises. in an endothermic reaction, heat is absorbed and the temperature of the system decreases.

in the gizmo, drag the thermometer into the flask of water.
a. what is the starting temperature?
b. click play, and wait for the reaction to end. what is the final temperature?
c. was this reaction exothermic or endothermic?

Explanation:

Step1: Identify starting temperature

The starting temperature is given as $21^{\circ}C$.

Step2: Identify final temperature

The final temperature is given as $50^{\circ}C$.

Step3: Determine reaction type

Since the final temperature ($50^{\circ}C$) is higher than the starting temperature ($21^{\circ}C$), heat is released, so it is an exothermic reaction.

Answer:

A. $21^{\circ}C$
B. $50^{\circ}C$
C. exothermic