Chemical Reaction Evidence

What observation would provide the best evidence that a chemical reaction occurred?

The scientist spilled dilute hydrochloric acid (HCl) on a lab table and sprinkled baking soda (NaHCO₃) onto the spill. Which observation would indicate a chemical reaction?

Best Evidence of Chemical Reaction

The observation that would provide the best evidence that a chemical reaction occurred is that the baking soda and hydrochloric acid combined, and bubbles formed.

When baking soda (NaHCO₃) and Hydrochloric Acid (HCl) combine, the following reaction happens:

NaHCO₃ + HCl → NaCl + H₂O + CO₂(g)↑

The gaseous Carbon Dioxide (CO₂) generated in this reaction is responsible for the bubbles. The releasing of this gas is evidence that a chemical reaction occurred between NaHCO₃ and HCl.

So, next time you see bubbles forming when baking soda and hydrochloric acid combine, you can be sure that a chemical reaction is taking place!