Chemical Reaction 

Chemical Reactions are the process in which new substance with new properties are form which involve chemical changes

• It Involves breaking of old chemical bonds which exist between the old substance which act to form new chemical bonds

A + B →AB

• During a chemical reactions atoms of one elements do not change in those of another elements Example:- Hydrogen react with oxygen to form water

2H₂ + O₂ → 2H₂O

Reactants 

• The Substance which takes part in chemical reactions are called Reactants

Products 

• The New Substance produced as a result of chemical reactions

Reactants→C (s) + O_{2 (g)} → Products→CO_{2 (g)}

• Here Reactants are transfer into products
• products properties are entirely different from Reactants

Characteristics of Chemical Reactions

⌈How can we know that chemical reactions happened ,     for this there are five characteristics ⌉

1. Change in State
2. Change in colour
3. Evolution of Gas
4. Change in Temperature
5. Formation of Precipitate

Change in state

H₂ (g)+ O_2(g) → H₂O(l)

                                                          Balance

2H₂ + 2O₂ → 2H₂O

Change in colour

Fe + CuSO₄ → FeSO₄ + Cu

• CuSO₄ -Copper sulphate
• Cu-Copper
• Fe-Iron
• FeSO_{4-Iron sulphate} 

Evolution of Gas 

Zn + H₂SO₄ → ZnSO₄ + H_{2   (Here hydrogen gas released )}

Change in Temperature 

CaO + H₂O → Ca(OH)_{2      (Rise in Temperature )} 

• Cao-quick lime
• Ca(OH)_{2-Slack lime} 

Formation of Precipitate 

when we mix two solution then a substance/particle shows like a solid at bottom of solution is called precipitate

A solid formed by a change in a solution often due to a chemical reaction or change in temperature that decreases solubility of  a solid.

Pb(NO₃) + KI → PbI₂ (Precipitate yellow colour)+ KNO₃

• Pb-lead
• (NO₃)-Nitrate
• KI-Potassium iodine
• KNO_{3-Potassium nitrate} 
• PbI_{2-lead Iodide}