Question

Which provides evidence that a chemical reaction occurs?

A) A gas is present
B) The total number of atoms remains unchanged
C) The state of matter remains the same
D) A brown gas is produced

Answer 1

In chemical reactions, the reactants and the products have the same components, with no new elements appearing or disappearing. Evidence that a chemical reaction occurs includes a change in color, the production of gas or a solid precipitate, and a transfer of energy. D) A brown gas is produced

Step-by-step explanation:

In chemical reactions, the components of the reactants—the elements involved and the number of atoms of each—are all present in the product(s). Similarly, there is nothing present in the products that are not present in the reactants. This is because chemical reactions are governed by the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.

The evidence that a chemical reaction occurs includes:

1. A change in color occurs during the reaction.
2. A gas is produced during the reaction.
3. A solid product called a precipitate is produced in the reaction.
4. A transfer of energy occurs as a result of the reaction.