4. For the reaction HCl + Ca CO3 -> Ca Cl2 + CO24a. Suggest 2 observations that makes you confirm a chemical reaction have taken place

To confirm that a chemical reaction has taken place in the reaction between hydrochloric acid (HCl) and calcium carbonate (CaCO₃), you can look for the following two observations:

1. Formation of Gas Bubbles: When HCl reacts with CaCO₃, carbon dioxide (CO₂) gas is produced. The appearance of effervescence or fizzing indicates that a gas is being evolved, confirming that a chemical reaction has occurred.

2. Change in Temperature: The reaction is also likely to be exothermic, meaning it can release heat. If you touch the reaction mixture and notice a temperature increase, this indicates that a chemical reaction has taken place.

These observations provide evidence for the occurrence of a chemical reaction.