Chemical Reactions and Equations

Introduction

• A chemical reaction is a process in which one or more substances are transformed into new substances.
• Example: Spoiling of food, rusting of iron.

Importance of Chemical Reactions

• The effect of medicines in the body, oxidation of food.

Signs of Chemical Change

• Change of color
• Emission of gas
• Change in temperature
• Example: Burning of fuel

Chemical Equation

• A means to represent reactants and products in a simple manner.
• Importance of a balanced chemical equation: According to the law of conservation of mass, the number of elements on both sides should be equal.

How to Balance

1. Balance polyatomic ions first.
2. Balance metals.
3. Balance non-metals.

Types of Reactions

1. Combination Reaction:

   • Two or more substances combine to form a new substance.
   • Example: H₂ + O₂ → H₂O

2. Decomposition Reaction:

   • A substance breaks down into two or more new substances.
   • Example: H₂O₂ → H₂O + O₂

3. Displacement Reaction:

   • An element displaces another element from its compound.
   • Example: Zn + HCl → ZnCl₂ + H₂

4. Double Displacement Reaction:

   • Exchange of ions between two compounds.
   • Example: Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

5. Combustion Reaction:

   • Burning of hydrocarbon with oxygen.
   • Example: CH₄ + 2O₂ → CO₂ + 2H₂O

Redox Reactions

• Combination of oxidation and reduction.
• Example: Fe + O₂ → Fe₂O₃
• Oxidation: Addition of oxygen or removal of hydrogen.
• Reduction: Removal of oxygen or addition of hydrogen.

Uses of Reactions in Life

• Rusting of iron.
• Aging of food products.

Conclusion

• Knowledge of chemical reactions and equations is extremely important in life.
• Understanding balancing and types of reactions is essential.