CLASS: X-SCIENCE
CHAPTER: CHEMICAL REACTIONS AND EQUATIONS-NOTES
1. Chemical
reactions-
The transformation of chemical substance into a new chemical substance by
making and breaking of bonds between different atoms is known as Chemical
Reaction.
2. Signs
of a chemical reaction- These factors denote that a chemical reaction
has taken place- change of state of substance, change of color of substance,
evolution of heat, absorption of heat, evolution of gas and evolution of light.
3. Chemical
Equation:
The representation of chemical reaction by means of symbols of substances in
the form of formulae is called chemical equation. E.g. - H2 + O2
⇒ H2O
4. Balanced
Chemical Equation: A balanced chemical equation has number atoms
of each element equal on both left and right sides of the reaction.
*Note-
According to Law of Conservation of Mass, mass can neither be created nor
destroyed in a chemical reaction. To obey this law, the total mass of elements
present in reactants must be equal to the total mass of elements present in
products.
5. Types
of Chemical Reactions-
I. Combination-
When two elements or one element and one compound or two compounds combines to
give one single product.
II. Decomposition-
Splitting of a compound into two or more simple products.
III. Displacement-
It takes place when a more reactive metal displaces a less reactive metal.
IV. Double
displacement- Reactions in which ions are exchanged between two reactants
forming new compounds are called double displacement reactions.
V. Precipitation-
The insoluble compound called precipitate forms in this reaction.
VI. Exothermic-
Reactions which produce energy are called exothermic reaction. Most of the
decomposition reactions are exothermic.
VII. Endothermic-
Reactions which absorb energy are called endothermic reaction. Most of the
combination reactions are endothermic.
VIII. Oxidation:
Gain of oxygen or removal of hydrogen or metallic element from a compound is
known as oxidation.
IX. Reduction:
Addition of hydrogen or removal of oxygen from a compound is called reduction.
X. Redox-
A chemical reactions where oxidation and reduction both take place
simultaneously are also known as redox reaction.
Eg
- NaOH + HCl ⇒ NaCl + H2O
6. Rusting- When iron reacts
with oxygen and moisture forms a red substance called rust.
7. Rancidity- Oils and fats
when get oxidized on exposure to air show a change in taste and smell.
8. Corrosion- Metals when
attacked by oxygen, water, acids, gases, present in air changes its surface
which is called corrosion.
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