Chapter 1: Chemical Reactions and Equations
1.1 Chemical Equations
1.1.1 Writing a Chemical Equation
- Chemical Equation: A symbolic representation of a chemical reaction using formulae of reactants and products.
- Reactants: Substances undergoing change in a reaction, written on the Left-Hand Side (LHS) with a plus sign (+).
- Products: New substances formed in a reaction, written on the Right-Hand Side (RHS) with a plus sign (+).
- Skeletal Equation: An unbalanced chemical equation where the count of atoms of each element on LHS is not equal to that on RHS.
1.1.2 Balanced Chemical Equations
- Law of Conservation of Mass: Mass can neither be created nor destroyed in a chemical reaction; total mass of elements in products must equal that in reactants.
- Balancing Equations: Equalizing the number of atoms of each element on both sides of the arrow using the hit-and-trial method.
- Physical States: Notations added for clarity: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solutions.
1.2 Types of Chemical Reactions
1.2.1 Combination Reaction
- Combination Reaction: A reaction where two or more reactants combine to form a single product.
- Exothermic Reactions: Chemical reactions accompanied by the release of heat (e.g., respiration, burning of natural gas).
1.2.2 Decomposition Reaction
- Decomposition Reaction: A reaction where a single reactant breaks down into two or more simpler products.
- Thermal Decomposition: Decomposition carried out by supplying heat energy.
- Electrolytic Decomposition: Decomposition carried out using electric current (e.g., electrolysis of water).
- Photolytic Decomposition: Decomposition triggered by light energy (e.g., silver chloride turning grey in sunlight).
1.2.3 Displacement Reaction
- Displacement Reaction: A chemical reaction in which a more reactive element displaces a less reactive element from its compound.
1.2.4 Double Displacement Reaction
- Double Displacement Reaction: A reaction where there is an exchange of ions between reactants to form new compounds.
- Precipitation Reaction: Any reaction that produces an insoluble solid (precipitate) in water.
1.2.5 Oxidation and Reduction
- Oxidation: The gain of oxygen or loss of hydrogen by a substance during a reaction.
- Reduction: The loss of oxygen or gain of hydrogen by a substance during a reaction.
- Redox Reaction: A reaction where oxidation and reduction occur simultaneously.
1.3 Effects of Oxidation Reactions in Everyday Life
1.3.1 Corrosion
- Corrosion: The gradual deterioration of metals due to interaction with moisture, air, acids, or chemicals (e.g., rusting of iron, black silver tarnish, green copper coating).
1.3.2 Rancidity
- Rancidity: The oxidation of fats and oils in food items, resulting in an unpleasant smell and taste.
- Prevention: Retarded by adding antioxidants, storing food in airtight containers, or flushing packaging with nitrogen gas.