Exam Oriented Chemistry Notes
CHEMICAL REACTIONS AND EQUATIONS
→ Chemical reaction
★ Reactant converted into product is called
chemical rection.
→ Changes occur in chemical reactions.
★ Change
in state
★ Change in temperature
★ Change colour
★ Gas evolved
→ Chemical equation
★ Symbolically representation of chemical
reaction.
→ Balanced chemical equation
★ Same number of atoms in LHS and RHS
→ Important balanced Chemical equations
1.
Hydrogen + Chlorine → Hydrogen chloride
H2 + Cl2 → 2HCl
2.
Sodium + Water → Sodium hydroxide + Hydrogen.
2Na + 2H2O → 2NaOH + H2
3.
Calcium carbonate → Calcium oxide + Carbon dioxide
CaCO3 → CaO + CO3
4.
Magnesium + Hydrochloric acid → Magnesium chloride + Hydrogen.
Mg + 2HCL → MgCl2 + H2
5.
Lead nitrate is heated.
2Pb(NO3)2 → 2PbO + 4NO2 + O2
6.
Sodium sulphate reacts with Barium chloride.
Na2SO4+ BaCl2 →
BaSO4+ 2NaCl
7.
Heating of ferrous sulphate crystals.
2FeSO4 → Fe2O3
+ SO2 + SO3
8.
Calcium oxide(quick lime) reacts with water.
CaO + H2O → Ca(OH)2 +
Heat
9.
Lime stone on heating
CaCO3 → CaO + CO2
10.
Burning of natural gas
CH4 + 2O2 → 2H2O
+ CO2
11.
Zinc reacts with copper sulphate solution.
Zn + CuSO4 → ZnSO4 +
Cu
12.
Zinc carbonate → Zinc oxide + Carbon dioxide
ZnCO3 → ZnO + CO2
13.
NaOH + H₂SO₄ → Na₂SO₄ + H₂O
2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O
14.
K + O2 →K2O
4K + O2 → 2K2O
15.
Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
Ca(OH)2 + CO2 →
CaCO3 +H2O
16.
Reaction of potassium metal with water
2K + 2H2O → 2KOH + H2
17.
Reaction of iron with copper sulphate solution
Fe + CuSO4 → FeSO4
+ Cu
18.
H2 + O2 → H2O
2H2 + O2 → 2H2O
19.
Na2CO3 + HCl → NaCl + H2O + CO2
Na2CO3 + 2HCl →
2NaCl + H2O + CO2
20. N2 + H2 → NH3
N2 + 3H2
→ 2NH3
21.
Sodium Chloride solution is added to silver nitrate solution.
NaCl + AgNO3 → NaNO3
+ Ag
22.
Lead
nitrate + Potassium iodide → Lead iodide + Potassium nitrate.
Pb(NO3)2 +
2KI PbI2 + 2KNO3
→ Types of chemical reactions
→ Combination
reactions
★ Two reactants combine to form one product.
Ex:
★ Calcium oxide(quick lime) react with water produce calcium hydroxide(slaked lime) and produce large amount of heat
CaO +
H2O → Ca(OH)2 +
Heat
(quick Lime) (slaked lime)
★ Burning
of coal:
C + O2 → CO2
★ Formation of water from hydrogen and oxygen gas.
H2 + O2 → H2O
→
Decomposition reaction
Thermal
decomposition:
★ One reactant breakdown to form two or more products
Ex:
★ Lime stone on heating
heat
CaCO3 →
CaO + CO2
(Lime stone) (quick
lime)
Quick lime used in the
manufacturing of cement
★ Lead nitrate is heated
heat
2Pb(NO3)2 → 2PbO + 4NO2 + O2
The
brown fume coming out when lead nitrate is heated is due to the liberation of Nitrogen
dioxide gas.
★ Heating of ferrous sulphate crystals.
heat
2FeSO4 → Fe2O3
+ SO2 + SO3
Ferrous
sulphate crystals lose green colour when heated. Because this
compound loses water molecule.
Electrolytic
decomposition (Electrolysis of water)
Ex: 2H2O → 2H2 + O2
★ In the electrolysis of water the gases that are released at cathode and anode and their ratio respectively are Hydrogen : Oxygen ; 2 : 1
★ The volume collected at one electrode is more than the other this is because water contains two parts of hydrogen element as compared to one part of oxygen element by volume.
★ Test the liberated gas: When a matchstick is brought near the gases evolved, hydrogen gas burns with a pop sound while oxygen gas being a supporter of gas make the matchstick burn brightly.
Photolytic
decomposition
sunlight
Ex: 2AgCl → 2Ag
+ Cl2
White silver chloride turns
grey in sunlight due to the decomposition of silver chloride into silver and chlorine
by light.
→ Oxidation
★ Addition of oxygen is called oxidation.
Ex:
★ 2Zn + O2 →2ZnO
★ 2Cu + O2 → Cuo
Copper
powder becomes coated with black copper oxide because oxygen added to copper
form copper oxide.
→ Reduction
★ Removing of oxygen is called reduction.
Ex: ZnO + C → Zn + CO
→ Redox
reaction
★ Oxidation and reduction occur in same
reaction.
Or
A chemical reaction in which
one reactant gets oxidised while the other gets reduced is called redox
reaction.
★ If a substance gains oxygen it said to oxidised.
★ If a
substance loses oxygen it said to reduced.
★ ZnO
+ C → Zn + CO
Carbo oxidised to CO and ZnO reduced Zn.
★ MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
HCl oxidised to Cl2 and MnO2
Reduced to MnCl2
★ Na + O2 →Na2O
Oxidized substance – Na, Reduced
substance - O2
★ CuO
+ H2 → Cu + H2O
Oxidized substance - H2, Reduced substance - CuO
→ Displacement
reaction
More reactive element displace the less
reactive element.
Ex:
Fe + CuSO4 → FeSO4
An iron nail is dropped into
a test tube having copper sulphate solution. The iron nail gradually turns to
brownish colour because iron is more reactive than copper, it displaces copper
from copper sulphate solution.
Fe2O3
+ 2Al → Al2O3 + 2Fe
Aluminium is more reactive than iron.
Zn +
CuSO4 → ZnSO4 + Cu
Pb +
CuCl2 → PbCl2 + Cu
→ Double
displacement reaction
★ Exchange of ions between reactants.
Ex: Na2SO4 +
BaCl2 → BaSO4 + 2NaCl
→ Precipitation
reaction
Insoluble
substance formed in the reaction.
Ex: Na2SO4 +
BaCl2 → BaSO4 + 2NaCl
★ Insoluble white precipitate is BaSO4
★ Ihe ions responsible for the formation of white precipitate is Ba2+ and SO42-
→ Exothermic
reaction
★ Heat released in the reaction.
Ex:
★ Burning
of natural gas:
CH4 + O2 → H2O +
CO2
★ Respiration
reaction in cell
C6H12O6
+ O2 → CO2 + H2O
+ Energy
★ Decomposition
of vegetable waste into compost
→ Endothermic
Reaction
Heat absorbed in the
reaction.
heat
Ex: CaCO3 →
CaO + CO2
→ Corrosion
★ Metals changes into undesirable substances by the action of atmosphere substance
Ex:
★ Black coating on silver
★ Green coating on copper
★ Rusting
of iron
→ Rancidity
★ Smell /taste of oil/fat containing substance
change by oxidation.
Prevention
★ Use Antioxidant
★ Refrigerating.
★ flushed with Nitrogen gas
★ Pack in air tight container
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