Module: Chemical Reactions and Equations
Class 10 (NCERT-Based with Olympiad and IIT-JEE Foundation Topics)
1. Introduction to Chemical Reactions
A chemical reaction is a process where reactants transform into products with new properties. It
involves breaking and forming of chemical bonds, leading to energy changes.
Key Characteristics of a Chemical Reaction:
1. Change in State: Solid to gas, liquid to gas, etc.
2. Change in Color: E.g., Blue copper sulfate turns white on heating.
3. Evolution of Gas: Bubbles observed in reactions like acid + metal.
4. Formation of Precipitate: Insoluble solid formed in a solution.
5. Change in Temperature: Exothermic (heat released) or endothermic (heat absorbed).
2. Chemical Equations
A chemical equation represents a reaction using symbols and formulas. It must be balanced to satisfy
the Law of Conservation of Mass.
Steps to Balance a Chemical Equation:
1. Write the unbalanced equation.
2. Count the number of atoms of each element on both sides.
3. Use coefficients to balance the atoms.
4. Ensure all atoms are balanced.
Example 1:
Unbalanced Equation:
H2+O2→H2OH2+O2→H2O
Balanced Equation:
2H2+O2→2H2O2H2+O2→2H2O
Example 2:
Unbalanced Equation:
Fe+H2O→Fe3O4+H2Fe+H2O→Fe3O4+H2
Balanced Equation:
3Fe+4H2O→Fe3O4+4H23Fe+4H2O→Fe3O4+4H2
3. Types of Chemical Reactions
1. Combination Reaction:
Two or more substances combine to form a single product.
General Form: A+B→ABA+B→AB
Example:
2Mg+O2→2MgO2Mg+O2→2MgO
2. Decomposition Reaction:
A single compound breaks down into two or more simpler substances.
General Form: AB→A+BAB→A+B
Types of Decomposition:
1. Thermal Decomposition: Heat is required.
Example: 2Pb(NO3)2→2PbO+4NO2+O22Pb(NO3)2→2PbO+4NO2+O2
2. Electrolytic Decomposition: Electricity is used.
Example: 2H2O→Electricity2H2+O22H2OElectricity2H2+O2
3. Photochemical Decomposition: Light is required.
Example: 2AgBr→Light2Ag+Br22AgBrLight2Ag+Br2
3. Displacement Reaction:
A more reactive element displaces a less reactive element from its compound.
General Form: A+BC→AC+BA+BC→AC+B
Example:
Zn+CuSO4→ZnSO4+CuZn+CuSO4→ZnSO4+Cu
4. Double Displacement Reaction:
Ions exchange between two compounds to form new compounds.
General Form: AB+CD→AD+CBAB+CD→AD+CB
Example:
Na2SO4+BaCl2→BaSO4+2NaClNa2SO4+BaCl2→BaSO4+2NaCl
5. Redox Reaction:
Oxidation (loss of electrons) and reduction (gain of electrons) occur simultaneously.
Example:
CuO+H2→Cu+H2OCuO+H2→Cu+H2O
• CuOCuO is reduced (gains H2H2).
• H2H2 is oxidized (loses electrons).
4. Oxidation and Reduction
Oxidation:
• Loss of electrons.
• Gain of oxygen.
• Loss of hydrogen.
Reduction:
• Gain of electrons.
• Loss of oxygen.
• Gain of hydrogen.
Example:
Zn+CuSO4→ZnSO4+CuZn+CuSO4→ZnSO4+Cu
• ZnZn is oxidized (loses electrons).
• Cu2+Cu2+ is reduced (gains electrons).
5. Corrosion and Rancidity
Corrosion:
Gradual destruction of metals by chemical reactions with the environment.
Example: Rusting of iron (4Fe+3O2+6H2O→4Fe(OH)34Fe+3O2+6H2O→4Fe(OH)3).
Rancidity:
Oxidation of fats and oils in food, leading to a bad smell and taste.
Prevention: Use of antioxidants, refrigeration, and airtight containers.
6. Advanced Topics (Olympiad and IIT-JEE Foundation)
1. Stoichiometry:
Calculation of reactants and products in a chemical reaction.
Example:
How many grams of O2O2 are required to burn 36g of CC?
Solution:
C+O2→CO2C+O2→CO2
1 mole of CC (12g) reacts with 1 mole of O2O2 (32g).
36g of CC requires 3212×36=96g1232×36=96g of O2O2.
2. Limiting Reagent:
The reactant that is completely consumed in a reaction.
Example:
If 2g of H2H2 reacts with 32g of O2O2, find the limiting reagent.
Solution:
2H2+O2→2H2O2H2+O2→2H2O
2g of H2H2 = 1 mole, 32g of O2O2 = 1 mole.
H2H2 is the limiting reagent.
3. Mole Concept:
1 mole = 6.022×10236.022×1023 particles.
Example:
Calculate the number of moles in 18g of H2OH2O.
Solution:
Molar mass of H2O=18g/molH2O=18g/mol.
Number of moles = 1818=11818=1 mole.
7. Practice Problems
1. Balance the equation:
NH3+O2→NO+H2ONH3+O2→NO+H2O
2. Identify the type of reaction:
AgNO3+NaCl→AgCl+NaNO3AgNO3+NaCl→AgCl+NaNO3
3. Calculate the mass of CO2CO2 produced when 24g of CC is burned.
