10 SCIENCE REVISION NOTES
CHAPTER 1 CHEMICAL REACTIONS AND EQUATIONS
Chemical reaction:
chemical reaction is the process where reactants are transformed into products.
These
are the following changes to determine that the chemical reaction has taken place:
★
Change in state
★
Change in colour
★
Evolution of gas
★ Change in temperature
Chemical
change: A change in which a new substance is formed is called
chemical change.
Examples: Rusting of iron, milk turning into curd
Physical
change: A change in which no new substances is formed is called
physical change.
Examples: Melting of ice, vaporisation of water on heating.
Chemical
Equation: A chemical equation is the symbolic representation of a
chemical reaction.
Examples: 2Mg
+ O2 →
2MgO
(Reactant) (Product)
Balanced
chemical equation:
★
The chemical equation needs to be balanced so
that it follows the law of conservation of mass.
★
In balanced chemical equation the number of
the atoms in the reactants side is equal
to the number of atoms in the products side.
Examples:
o
Zn(s) + H2SO4(aq) → ZnSO4(s)
+ H2(aq)
o
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(aq)
Types of chemical reaction:
Combination
reaction: a single product is formed from two or more reactants is
called combination reaction.
Examples:
o
CaO(s) + H2O(l)
→ Ca(OH)2(aq)
o
C(s) +
O2(g) → CO2(aq)
o H2(g) + O2(g) → H2O(aq)
Decomposition
reaction: single reactant breaks down to give two or more products
is called decomposition reaction.
Examples:
Heat
o
FeSO4(s) → Fe2O3(s) + SO2(g)
+SO3(g)
Heat
o
2Pb(NO2)3(s) → 2PbO(s)
+ 4NO2(g) + O2(g)
Sunlight
o
2AgCl(s)
→ 2Ag(s) + Cl2(g)
Sunlight
o
2AgBr(s)
→ 2Ag(s) + Br(g)
Electricity
o
2H2O(l) → 2H2(g)
+ O2(g)
Electrolysis
of water:
Cathod:
H2 gas
Anod: O2 gas
Displacement
reaction: More reactive
element displaces a less reactive element is called Displacement reaction.
Examples:
o
Fe(s) + CuSO4(aq) → FeSO4(g) + Cu(s)
o Pb(s) + CuCl2(aq) → PbCl2(aq) + Cu(s)
Double
Displacement reaction: Exchange of ions between the reactants
is called double displacement reaction.
Examples:
Na2(SO)4(aq)
+ BaCl2(aq) → BaSO4(s) + NaCl(aq)
(White
ppt)
A chemical reaction in which an insoluble substance formed is called precipitation reaction.
Exothermic
reaction: Heat energy produced in the reaction is called
exothermic reaction.
Examples:
CH4(g) + 2O2 (g) → CO2 (g) + 2H2O(g)
Endothermic
reaction: Heat energy absorbed by the reaction is called endothermic
reaction.
Heat
Examples: CaCO3(s) → CaO(s) + CO2(g)
Oxidation
reaction: A reaction in which oxygen is added or hydrogen is
removed is called oxidation reaction.
Examples: 2Cu + O2 → 2CuO
Reduction
reaction: A reaction in which oxygen is removed or hydrogen is
added is called reduction reaction.
Examples: ZnO + C → Zn + CO
Redox
reaction: A reaction in which both oxidation reduction takes place
is called redox reaction.
Examples:
Oxidized substance – H2
Reduced substance – CuO
Corrosion: The process of slow conversion of metals into their undesirable compounds due to their reaction with oxygen, water, acids, gases etc. present in the atmosphere is called corrosion.
Examples:
★ The black coating formed on the surface of silver is silver carbonate
★ The green coating on copper is copper carbonate.
★ Rusting of iron.
Prevention of corrosion:
★ Painting
★ Oiling and greasing
★ Allying
★ Galvanising
Rancidity:
★ The taste and odour of food materials containing fat and oil changes when they are left exposed to air for long time. This is called rancidity.
★ It is caused due to oxidation of fat and oil present in food material.
Prevention of corrosion:
★ Adding antioxidants
★ Storing food in air tight container
★ Flushing out air with nitrogen
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