What are some evidences of a chemical reaction?

Answer 1

Evidences For Chemical Change

Chemical changes produce new substances from starting substances, and distinguishing a chemical change from a physical change is based on detecting new substances in the system being observed. When two or more materials (reactants) are mixed, four easily observed indicators for new materials are:

1) formation of a gas from two liquids or a liquid and a solid.

2) formation of a solid (precipitate) from two liquids or a gas and a liquid.

3) unexpected color change. For example, mixing two colorless liquids and obtaining a color is an unexpected color change but mixing a blue liquid and yellow liquid and obtaining a green liquid is not an unexpected color change.

4) dissolving an insoluble solid (precipitate) in a solution. Note, the solution's solvent in this case will not dissolve the solid by itself.

Not all chemical reactions exhibit these changes in properties, and evidence for new substances must then be obtained from other observations. Instruments which extend our ability to make observations are often employed to detect such chemical changes.

from: www.baruch.edu/wsas/departments/ natural_science/chemistry/chm_1000/chm_magic.doc

Answer 2

There can be several ways in order to tell if a reaction has taken place. Here are only a few :

• Gas bubbles released
• Colour change
• Change in mass
• Formation of precipitates
• Change in physical state
• ...

Sometimes you cannot see/calculate a change however you will need more accurate equipment in order to do so.

Answer 3

Some indicators of a chemical reaction are:

- change of color

- change of odor

- release of a gas

- change of the temperature

- change of the viscosity

- formation of a precipitate

- change of general appearance

- possible explosion

- possible chemiluminiscence

- formation of new compounds

Answer 4

-Heat released

-Light released

-Bubbling (not to be confused with boiling)

-Precipitate formed

-Change of color

Answer 5

1) Formation of a gas
2) A permanent color change is observed
3) Formation of a solid
4) Dissolution of an insolubale solid

Answer 6

change in temperature

formation of a precipitate

formation of a gas

disappearance of a solid

change in color

change in odor

Answer 7

-Change of colour.

-Release of gas.

-Remain of precipitate.

-Release of energy.