2. CHEMICAL REACTIONS
CHEMICAL REACTIONS ARE THE PROCESSES IN WHICH NEW
SUBSTANCES WITH NEW PROPERTIES ARE
FORMED.CHEMICAL REACTIONSINVOLVE CHEMICAL
CHANGES. DURING CHEMICAL REACTIONS, A
REARRANGEMENT OF ATOMS TAKE PLACE BETWEEN THE
REACTING SUBSTANCE TO FORM NEW SUBSTANCES HAVING
ENTIRELY DIFFERENT PROPERTIES. CHEMICAL REACTIONS
INVOLVE BREAKING OF OLD CHEMICAL BONDS WHICH
EXIST BETWEEN THE REARRANGED ATOMS OF NEW
SUBSTANCES. DURING A CHEMICAL REACTIONS, ATOMS OF
ONE ELEMENT DO NOT CHANGE INTO THOSE OF ANOTHER
ELEMENT. ONLY A REARRANGEMENT OF ATOMS TAKE PLACE
IN A CHEMICAL REACTIONS.
EXAMPLE
MAGNESIUM+OXYGEN----------------MANGESIUMOXIDE
3. REACTANTS AND PRODUCTS
THE SUBSTANCE WHICH TAKE IN A CHEMICAL REACTION
ARE CALLED REACTANTS.
EXAMPLE:-
METHANE+OXYGEN IS REACTANT
THE NEW SUBSTANCE PRODUCED AS A RESULTS OF
CHEMICAL REACTION ARE CALLED PRODUCTS.
EXAMPLE :-
CARBON DIOXIDE+WATER
4. CHARACTERISITICS OF CHEMICAL REACTIONS
EVOLUTION OF A GAS,
FORMATION OF A PRECIPITATE
CHANGE IN COLOUR
CHANGE IN TEMPERATURE
CHANGE IN STATE
5. EVOLUTION OF A GAS
SOME CHEMICAL REACTIONS ARE CHARACTERISED BY THE
EVOLUTION OF A GAS.
A PRECIPITATE IS A ‘SOLID PRODUCT’WHICH SEPARATES OUT
FROM THE SOLUTION DURING A CHEMICAL REACTIONS. A
PRECIPITATE CAN BE FORMED BY MIXING AQUEOUS
SOLUTIONS(WATER SOLUTIONS)OF REACTANTS WHEN ONE
OF THE PRODUCTS IS INSOLUBLE IN WATER. A PRECIPITATE
CAN ALSO BE FORMED BY PASSING A GAS INTO AN AQUEOUS
SOLUTION OF A SUBSTANCE.
EXAMPLE:-
ZN+H2SO4-------ZNSO4+H2
6. FORMATION OF A PRECIPITATE
SOME CHEMICAL REACTIONS ARE CHARACTERISED BY THE
FORMATION OF A PRECIPITATE.
THE REACTIONS IN WHICH PRECIPITATE IS FORMED IS
FORMED ARE CALLED PRECIPITATE REACTIONS.
EXAMPLE:-
pb(NO3)2+pbI2+KNO3
PBI2 IS YELLOW PRECIPITATE
7. CHANGE IN COLOUR
SOME CHEMICAL REACTIONS ARE CHARACTERISED BY A CHANGE
IN COLOUR.
BEFORE WE GO FUTHER, WE SHOULD KNOW WHY TEMPERATURE
CHANGE TAKES PLACE IN CHEMICAL REACTIONS.CHEMICAL
REACTIONS OFTEN PRODUCES HEAT ENERGY. WHEN A CHEMICAL
REACTIONS PRODUCES HEAT ENERGY,THEN THE TEMPERATURE
OF REACTIONS MIXTURE RISESAND IT BECOMES HOT. IN SOME
CASES,HOWEVER, CHEMICAL HEAT ENERGY, THEN THE
TEMPERATURE OF REACTIONS MIXTURE FALLS AND IT BECOMES
COLD.
EXAMPLES:-
ZN+CUSO4-----------ZNSO4+CU
8. CHANGES IN TEMPERATURE
SOME CHEMICAL REACTIONS ARE CHARACTERISED BY A
CHANGES IN TEMPERATURE.
THERE ARE TWO TYPES REACTIONS:-
EXOTHERMIC REACTIONS
ENDOTHERMIC REACTIONS
9. ENDOTHERMIC AND EXOTHERIC REACTIONS
THE REACTIONS IN WHICH ENERGY IS ABSORBED IS
CALLED AN ENDOTHERMIC REACTION.
EXAMPLES:-
CaCO3---------CaO+CO2
THE REACTIONS IN WHICH ENERGY IS RELEASED IS
CALLED AN EXOTHEMIC REACTIONS.
EXAMPLE:-
C+O2--------CO2+HEAT
10. CHANGES OF STATE
SOME CHEMICAL REACTIONS ARE CHARACTERISED BY A
CHANGE IN STATE.
THERE ARE SOMES CHEMICAL REACTIONS WHICH CAN
SHOW MORE THAN ONE CHARACTERISTICS.
EXAMPLE:-
ZNSO4+H2----------ZN+H2SO4
