Introduction:
Chemical reactions are the processes in which substances interact to form new substances with different chemical properties. There are several evidences that can be observed to determine whether a chemical reaction has occurred or not. These evidences include changes in color, formation of precipitate, evolution of gas, changes in temperature, and changes in physical properties.

Evidences of a Chemical Reaction:

1. Color Change:
- A color change is often a clear indication of a chemical reaction taking place.
- For example, when iron rusts, it undergoes a chemical reaction with oxygen in the air, resulting in the formation of iron oxide, which is a different color than the original iron.

2. Formation of Precipitate:
- A precipitate is a solid substance that forms when two solutions are mixed together.
- When a chemical reaction occurs, it may result in the formation of a precipitate, which indicates that a new substance has been formed.
- For example, when silver nitrate solution is mixed with sodium chloride solution, a white precipitate of silver chloride is formed.

3. Evolution of Gas:
- The evolution of gas is a common evidence of a chemical reaction.
- When certain substances react, they may produce gas as a byproduct, which can be observed as bubbles or fizzing.
- For example, when vinegar (acetic acid) is mixed with baking soda (sodium bicarbonate), carbon dioxide gas is produced, resulting in the fizzing of the mixture.

4. Changes in Temperature:
- Chemical reactions often involve the absorption or release of energy in the form of heat.
- Therefore, changes in temperature can be an evidence of a chemical reaction.
- For example, when magnesium reacts with hydrochloric acid, the reaction is exothermic and releases heat, leading to an increase in temperature.

5. Changes in Physical Properties:
- Chemical reactions can also result in changes in physical properties, such as texture, density, or state of matter.
- For example, when wood burns, it undergoes a chemical reaction with oxygen, resulting in the transformation of solid wood into ash and gases.

Conclusion:
Observing the evidences of a chemical reaction, such as color change, formation of precipitate, evolution of gas, changes in temperature, and changes in physical properties, can help in identifying and confirming the occurrence of a chemical reaction. These evidences provide tangible proof that new substances with different chemical properties have been formed.

Yes; new substances formed, as evidenced by the color changes and bubbles. Some signs of a chemical change are a change in color and the formation of bubbles. The five conditions of chemical change: color change, formation of a precipitate, formation of a gas, odor change, temperature change.