Question

A food item that is left out of the refrigerator turns brown and forms bubbles and gas. What are the signs that this is a chemical reaction? Check all that apply.
A: Heat is produced.

B: Heat is absorbed.

C: Bubbles appear.

D: A precipitate forms.

E: The color changes.

Answer 1

The answers would be:

C. Bubbles appear

E. The color changes

If you'd like to know more, you can read on:

Although your selections are indications of chemical reactions, if you are referring to only the chemical reaction that occurred in your example, then the two answers are the only choices.

A chemical reaction occurs when the reactants form a new product. Signs of a chemical reaction include change is smell, color and temperature. In some cases, precipitate forms.

Answer 2

Answer: C: Bubbles appear E: The color changes.

Explanation:

A chemical reaction is defined as the reaction in which a change in chemical composition takes place. A new substance is formed in these reactions.

Example: Oxidation of iron to ferric oxide is a chemical change.

$4Fe(s)+3O_2(g)\rightarrow Fe_2O_3(s)$

Here iron which is grey in color changes first to green and then turns brownish red.

Characteristics of a chemical reaction:

1. change in color

2. heat is gained or lost

3. evolution of gas

4. formation of precipitate

Thus when a food item that is left out of the refrigerator changes colour  and evolution of gas takes place and thus would be a chemical change.