to tell if a chemical reaction has occurred look for these four things:
1) color change
2) the formation of gas bubbles
3) formation of a precipitate
4) temperature change
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precipitation
evolution of gas
change of odor
change of color
change of viscosity
change of temperature
change of pH
visible formation of a new compound
The formation of white precipitate indicates a chemical reaction occurred in the beaker that resulted in the precipitation of a solid product from the solution.
Whether a reaction took place is determined by the change in chemical composition, the formation of new substances, the release of energy or heat, and the color change or visible evidence of a chemical change. These factors indicate that a chemical reaction has occurred.
Dissolving salt in water is a physical change because the salt molecules stay intact and only disperse in the water, without undergoing a chemical reaction.
When CO2 reacts with limewater (calcium hydroxide), the solution turns milky due to the formation of calcium carbonate, which is insoluble and precipitates out. This indicates a chemical reaction has taken place as a new substance with different properties has formed.
A product is a substance formed after a chemical reaction from the reactants involved in the process. It is the result of the reaction and can be a single compound or a mixture of compounds that were not present before the reaction took place.