Question

When calcium carbonate and hydrochloric acid react, bubbles form. how do you know a reaction occurred? a gas was formed a precipitate was formed a color change happened the volume changed?

Answer 1

The reason that you can tell that it was chemical is because you can see the bubbles forming. This means that it is giving off a gas.

Answer 2

Answer: The indicator that indicates the reaction has occurred is the formation of gas.

Explanation:

The common indicators of a chemical change has occurred are:

• Release of gas from the reaction.
• Formation of bubbles.
• Color change
• Temperature change
• Formation of a precipitate
• Specific odor

The chemical equation for the reaction of calcium carbonate and hydrochloric acid follows:

$CaCO_3(s)+2HCl(aq.)\rightarrow CaCl_2(s)+H_2O(l)+CO_2(g)$

As, we can see, gas (carbon dioxide) is being released during the reaction with effervescence.

Hence, the indicator that indicates the reaction has occurred is the formation of gas.