Question

Which actions are evidence that a chemical reaction has occurred? Check all that apply. a change in color the formation of a precipitate a clear liquid becoming cloudy a change in shape the formation of bubbles the formation of smoke

Answer 1

Answer:

1. a change in color
2. the formation of a precipitate
3. the formation of bubbles

Explanation:

In a chemical reaction, there is always a rearrangement of atoms within the molecules of reactants to form new products. Such a change is different from changes in the physical form of molecules, e.g. shape.

Thus, according to this criteria, only three options are correct in the given question. A change in color is definitely an indication of chemical reaction because the emission of light before and after cannot be changed unless molecules are rearranged to form a new chemical. Likewise, precipitates form when a reaction takes place between chemically dissolved molecules to form less or not dissolvable compounds. In the end, the configuration of bubbles also indicates that the reaction has taken place because new gases are being released.

On the other hand, change in shape is a physical change because the composition doesn't need to also been changed. An example is the ice formation from water. Same is the case with "change of clear liquid to cloudy" because the addition of non-reactive substances could change the nature of liquid to cloudy however the reaction doesn't need to have taken place.

Answer 2

Answer:

1 a change in color

2 the formation of a precipitate

3 the formation of bubbles

Explanation: