Chapter 1: Chemical Reactions and Equations

1. Introduction to Chemical Reactions

• Definition: A process that leads to the transformation of one set of chemical substances to another.
• Types of Chemical Reactions:
  • Combination Reaction: Two or more substances react to form a single product.
    • Example:  CaO+H₂O→Ca(OH)₂
  • Decomposition Reaction: A single compound breaks down into two or more substances.
    • Example:  CaCO₃→ΔCaO+CO₂
  • Displacement Reaction: One element displaces another in a compound.
    • Example:  Zn+CuSO₄→ZnSO₄+Cu
  • Double Displacement Reaction: Ions of two compounds exchange places to form new compounds.
    • Example:  Na₂SO₄+BaCl₂→BaSO₄+2NaCl
  • Oxidation and Reduction:
    • Oxidation: Loss of electrons or increase in oxidation state.
    • Reduction: Gain of electrons or decrease in oxidation state.
    • Example of Redox Reaction: 

CuO+H₂→Cu+H₂O

2. Chemical Equations

• Writing Chemical Equations:
  • Reactants on the left side, products on the right side.
  • Use '+' to separate different entities, '→' to show the direction of the reaction.
  • Example:  
• Balancing Chemical Equations:
  • Law of Conservation of Mass: The number of atoms of each element must be the same on both sides of the equation.
  • Steps:
    1. Write the skeletal equation.
    2. Count the number of atoms of each element on both sides.
    3. Use coefficients to balance (start with the most complex molecule).
    4. Check if the equation is balanced.

Mg+O₂→MgO

3. Types of Chemical Changes Indicated by Chemical Reactions

• Change in State: Solid to liquid, gas, etc.
• Change in Color: Example, rusting of iron (orange-brown color).
• Evolution of Gas: Bubbles or effervescence.
• Change in Temperature: Exothermic or endothermic reactions.
• Formation of Precipitate: Insoluble substance forms.

4. Effects of Oxidation Reactions in Everyday Life

• Corrosion: Rusting of iron, tarnishing of silver.
• Rancidity: Degradation of fats and oils when exposed to air, leading to bad smell and taste.

5. Practical Applications

• Prevention of Rusting: Painting, galvanizing, alloying.
• Use of Antioxidants: To prevent food from getting rancid.

Summary:

• Understanding chemical reactions involves recognizing how substances interact to form new compounds, the balancing of equations to maintain mass conservation, and observing the physical and chemical changes that indicate reactions have occurred.