A student investigating chemical reactions adds two tablets containing citric acid and baking soda to water. Which of the following is evidence that a chemical reaction occurred?

Question

A student investigating chemical reactions adds two tablets containing citric acid and baking soda to water. Which of the following is evidence that a chemical reaction occurred?

A. The tablet gradually becomes smaller until there is nothing left

B. Bubbling occurs as a new substance carbon dioxide is produced

C. The temperature of the liquid stays the same

D. The tablets gradually sink to the bottom of the container

Answer 1

B. Bubbling occurs as a new substance carbon dioxide is produced. This is evidence of a chemical reaction, as the reactants (citric acid and baking soda) are producing a new substance (carbon dioxide) with different physical and chemical properties than the reactants themselves. Option A may indicate a physical change, but not necessarily a chemical one. Option C and D are not indicators of a chemical reaction.