Chapter 1
Chemical Reactions and Equations
Preview Chemical Reactions and Equations for Science in JAC 10.
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Notes
- Chapter Revision (Quick Revision) Chemical Reaction
A process in which one or more substances change into new substances having different properties is called a chemical reaction.
Indicators of Chemical Reaction Change in colour Evolution of gas Change in temperature Formation of precipitate Change in state
Example:
2Mg+O 2
→2MgO
Magnesium burns with a bright white flame and forms magnesium oxide.
- Chemical Equations Word Equation
Magnesium + Oxygen → Magnesium Oxide
Skeletal Equation
Mg + O₂ → MgO
Balanced Equation 2Mg+O 2
→2MgO
Balancing is done according to the Law of Conservation of Mass.
- Types of Chemical Reactions A. Combination Reaction
Two or more substances combine to form a single product.
General form:
A + B → AB
Example:
CaO+H 2
O→Ca(OH) 2
+Heat
Quicklime + Water → Slaked lime
B. Decomposition Reaction
One compound breaks into simpler substances.
General form:
AB → A + B
(i) Thermal Decomposition CaCO 3
Heat
CaO+CO 2
(ii) Electrolytic Decomposition 2H 2
O Electricity
2H 2
+O 2
(iii) Photolytic Decomposition 2AgCl Sunlight
2Ag+Cl 2
C. Displacement Reaction
A more reactive element displaces a less reactive element.
General form:
A + BC → AC + B
Example:
Zn+CuSO 4
→ZnSO 4
+Cu D. Double Displacement Reaction
Exchange of ions between two compounds.
Example:
BaCl 2
+Na 2
SO 4
→BaSO 4
+2NaCl
White precipitate of BaSO₄ is formed.
E. Precipitation Reaction
Formation of an insoluble substance.
Example:
BaCl₂ + Na₂SO₄ → BaSO₄↓
F. Oxidation and Reduction Oxidation
Addition of oxygen or removal of hydrogen.
Example:
2Cu+O 2
→2CuO Reduction
Removal of oxygen or addition of hydrogen.
Example:
CuO+H 2
→Cu+H 2
O Redox Reaction
Oxidation and reduction occur simultaneously.
Example:
CuO+H 2
→Cu+H 2
O 4. Exothermic and Endothermic Reactions Exothermic Reaction
Heat is released.
Example:
CH 4
+2O 2
→CO 2
+2H 2
O+Heat
Examples:
Respiration Burning of fuels Endothermic Reaction
Heat is absorbed.
Example:
Photosynthesis
- Corrosion
Slow destruction of metals by action of air and moisture.
Example:
Rusting of iron
4Fe+3O 2
+xH 2
O→2Fe 2
O 3
.xH 2
O
Prevention:
Painting Greasing Galvanization Alloy formation 6. Rancidity
Oxidation of oils and fats causing unpleasant smell and taste.
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