CHAPTER-1�Chemical reactions and Equations
PREPARED BY
D S SAMKUTTY PGT CHEMISTRY
JNV PATHANAMTHITTA
NAVODAYA VIDYALAYA SAMITI, NOIDA
E-CONTENT FOR CLASS X SCIENCE
Chemical Reaction
It is a process in which one or more substances are formed as new substances
And it cannot be reversed by physical methods
Chemical reaction involves
Chemical Reactions happen in our daily life
Reactants : The substances which take part in chemical reaction are called reactants
Products: The substances which are formed during chemical reaction are called products
When Magnesium burns in air gives Magnesium oxide
Magnesium + Oxygen(air) --🡪 Magnesium oxide
Reactants- Magnesium and Air
Product- Magnesium oxide
Chemical Equation
A chemical reaction can be represented by a chemical equation
It involves use of symbols of substances of reactants and products ith mention of their physical states.
When Magnesium ribbon burns in oxygen ( air ) gives Magnesium oxide
Mg(s) + O2(g) ------------🡪 MgO(s)
Solid –(s)
Iiquid-(l)
Gas-(g)
Aqueous-(aq)
Aqueous solution: It is solution in which water is solvent
What is the need of balancing a chemical Equation?
Law of Conservation of Mass : It states that matter can neither be created nor be destroyed during a chemical reaction.
So the number of elements ( atoms ) involved in a chemical reaction should be same on reactants side and product side
How to balance a Chemical Reaction?
Fe + H2O --🡪 Fe2O3 + H2
2 Fe + 3 H2O ---🡪 Fe2O3 + 2H2
Elements | LHS | RHS |
Fe | 1 x | 2 |
H | 2 x | 2 x |
O | 1x | 3 |
Types of Chemical Reactions
2. Decomposition Reactions
3. Displacement Reactions
4. Double Displacement Reactions
5. Precipitation Reactions
6. Redox Reactions
Combination Reactions
These are the reactions in which two or more substances combine to form a single product.
A + B ---🡪 AB
Addition of water to quick lime
CaO + H2O ---------------🡪 Ca(OH)2
Burning of Coal
C(s) + O2(g) ---🡪 CO2(g)
Formation of Water
H2(g) + O2(g)---🡪 H2O(l)
Decomposition Reactions
These are the reactions in which a single substance breaks down into two or more substances.
AB-------🡪 A + B
Decomposition can be effected by
Heat ( Thermal decomposition)
Electricity ( Electrolysis)
Light (Photolysis)
Decomposition by Heat (Thermal Decomposition)
Decomposition of Ferrous sulphate
Heat
2FeSO4(s) ---------------🡪 Fe2O3(s) + SO2(g) + SO3(g)
(green) (red) (Smell of burned Sulphur)
Decomposition of Lead nitrate
Heat
2Pb(NO3)2 ---------------------🡪 2PbO + 4 NO2 + O2
( brown fumes)
Decomposition by Electricity ( Electrolysis)
Decomposition of Water (Electrolysis of water)
Electricity
H2O (l) --------------🡪 H2(g) + O2(g)
H2 and O2 formed in the ratio 2:1
Decomposition by Light ( Photolysis)
Silver chloride exposed to sunlight
sunlight
2AgCl(s) -------------------------🡪 2Ag(s) + Cl2(g)
white grey
Photosynthesis
sunlight
6 CO2 + 6H2O --🡪 C6H12O6 + 6O2
Displacement Reactions
These are the reactions in which a more reactive element displace a less reactive element from its solution.
Fe(s) + CuSO4(aq) ----------🡪 FeSO4(aq) + Cu(s)
Double Displacement Reactions
These are the reactions in which new compounds are formed by the mutual exchange of ions between two compounds.
Na2SO4(aq) + BaCl2(aq) ----🡪 BaSO4(aq) + 2 NaCl(aq)
(sodium Sulphate) (Barium Chloride) (Barium sulphate) (Sodium chloride)
(precipitate-white)
Precipitate-It is an insoluble substance formed.
Pb(NO3)2 + 2 KI ----🡪 PbI2 + 2 KNO3
(lead nitrate) (potassium iodide) (lead iodide) (potassium nitrate)
( yellow ppt)
Redox Reactions
Reactions in which oxidation and Reduction together takes place
Oxidation: Addition of oxygen or removal of hydrogen from a substance
2Cu + O2 ----🡪 2CuO
Reduction :Removal of oxygen or addition of hydrogen to a substance
CuO + H2 ----🡪 Cu + H2O
REDuction + Oxidation = REDOX reaction
Oxidation in Daily Life
(i)Corrosion
Destruction of a metal by the action of environmental conditions
Rusting of iron (Hydrated ferric oxide)
Tarnishing of silver ( formation of black coating on silver )
Verdigris on copper ( Green coating on copper)
(ii) Rancidity
The oxidation of fats and oils when exposed to air is known as rancidity . It leads to bad smell and bad taste of food
Exothermic Reactions :These are the reactions which take place with
the liberation of energy
is liberated.
Ex : Burning of Coal
C (s) + O2(g) ----🡪 CO2(g) + heat
Burning of Natural gas
CH4(g) + O2(g) -----------🡪 CO2(g) + H2O(g) + heat
Respiration
C6H12O6 (aq) + O2(g) -----🡪 CO2(g) + H2O(l) + energy
Endothermic Reactions :These are the reactions which takes place
with the absorption of energy.
heat
CaCO3(s) -----------------🡪 CaO(s) + CO2(g)
light
2AgCl (s) --------------🡪 2 Ag(s) + Cl2(g)
Thank You