jesc101

Chemical Reactions and Equations

Daily Life Observations

• Situations to Consider:

  • Milk left at room temperature during summer.

  • Iron exposed to humid atmosphere (rusting).

  • Fermentation of grapes.

  • Cooking food.

  • Digestion in the body.

  • Respiration.

• Each scenario indicates a change in the identity and nature of substances, reflecting physical or chemical changes.

Understanding Chemical Reactions

• Definition of Chemical Reaction:

  • A process that involves the transformation of substances, where the identity of the initial substance changes.

• Determining a Chemical Reaction:

  • Conducting activities to observe changes can demonstrate the occurrence of chemical reactions.

Activities Demonstrating Reactions

Activity 1.1: Burning Magnesium Ribbon

• Materials Needed: Magnesium ribbon (3-4 cm), spirit lamp/burner, watch-glass.

• Procedure:

  1. Clean magnesium ribbon with sandpaper.

  2. Burn it carefully with tongs and collect ash in watch-glass.

• Observations:

  • Formation of a dazzling white flame and white powder (magnesium oxide).

Activity 1.2: Formation of Hydrogen Gas

• Materials: Zinc granules, dilute sulphuric acid.

• Observations: Observe changes in zinc granules and temperature after adding acid.

Chemical Equations

Writing Chemical Equations

• Word-Equation Example:

  • Magnesium + Oxygen → Magnesium Oxide

  • Reactants: Magnesium, Oxygen; Product: Magnesium Oxide.

• Symbolic Representation:

  • Chemical Equation: Mg + O2 → MgO

Balancing Chemical Equations

• Law of Conservation of Mass: Total mass of reactants = Total mass of products.

• Example of a Balanced Equation:

  • Zinc + Sulphuric Acid → Zinc Sulphate + Hydrogen

  • Zn + H2SO4 → ZnSO4 + H2

Steps to Balance an Equation

1. Identify reactants/products: Draw boxes around each formula.

2. Count atoms for each element on both sides: Ensure they are equal.

3. Adjust coefficients: To balance the atoms without changing formulas.

4. Physical States: Indicate if reactions are solid (s), liquid (l), gas (g), or aqueous (aq) in balanced equations.

   • Example: 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)

Types of Chemical Reactions

1. Combination Reaction

• Definition: Two or more reactants combine to form a single product.

• Example:

  • CaO + H2O → Ca(OH)2

• Exothermic Reaction: Releases heat.

2. Decomposition Reaction

• Definition: A single reactant breaks down into multiple products.

• Examples:

  • 2FeSO4(s) → Fe2O3(s) + SO2(g) + SO3(g)

  • CaCO3(s) → CaO(s) + CO2(g)

  • Thermal decomposition involves heat.

3. Displacement Reaction

• Definition: One element displaces another in a compound.

• Example:

  • Fe + CuSO4 → FeSO4 + Cu

4. Double Displacement Reaction

• Definition: Exchange of ions between two reactants.

• Example:

  • Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)

Oxidation and Reduction Reactions

• Oxidation: Gain of oxygen/loss of hydrogen.

• Reduction: Loss of oxygen/gain of hydrogen.

Everyday Effects of Oxidation

1. Corrosion

• Definition: Deterioration of metals due to chemical reactions with the environment (e.g., rusting of iron).

• Consequences: Economic loss and structural issues.

2. Rancidity

• Definition: Change in taste and smell of fats/oils due to oxidation.

• Prevention Methods: Use of antioxidants or air-tight storage.

Key Points to Remember

• Complete chemical equations include reactants, products, and their physical states.

• Equations must be balanced; conservation of mass must hold true.

• The classification of reactions: combination, decomposition, displacement, double displacement.

• Understanding oxidation-reduction is critical for recognizing chemical changes.

• Recognizing daily life examples helps in understanding chemical processes.