Hannah does an experiment. She has two colorless chemicals that she mixes together in a beaker. Which of the following indicates that a chemical change occurs when she mixes the two chemicals together?

Question

I. The chemicals change color from colorless to purple.
II. A yellow gas forms.
III. A brown solid forms in the bottom of the beaker.
IV. The temperature of the chemicals rises 15°C.
A.
I and III only
B.
I, II, and III only
C.
I, II, III, and IV
D.
II and III only

Answer 1

A chemical change is indicated by any change that affects the composition of the substances involved. In this case, all the observations mentioned suggest a chemical change:

I. The chemicals change color from colorless to purple. (Indicates a change in chemical composition)

II. A yellow gas forms. (Indicates a new substance is produced)

III. A brown solid forms in the bottom of the beaker. (Indicates a new substance is produced - precipitate formation)

IV. The temperature of the chemicals rises 15°C. (Indicates an exothermic reaction, which is often associated with a chemical change)

Based on this analysis, the correct answer is:

C. I, II, III, and IV