This document discusses four key characteristics of chemical reactions: 1) Evolution of gas, where reactions produce gaseous products like in reactions where gas is evolved; 2) Change of color, as certain reactions exhibit color changes; 3) Formation of precipitation, where reactions produce insoluble substances; and 4) Change of state, as some reactions involve changes in the state of compounds.

1. Characteristics of Chemical Reaction
Evolution of Gas
Change of color
Formation of precipitation
Change of state

2. 1) Evolution of gas during chemical reaction
In many chemical reaction one of the product is gas , lets have the
example

3. Change of color in chemical reactions
Certain chemical reaction depicts some change of color Effervescence

4. Formation of precipitation (ppt)
Certain chemical often end up producing an insoluble
substance know as precipitation

5. Change of state Many reaction involve the change of state of the
compound .