Overview
This lecture covers the Class 10 chapter "Chemical Reactions and Equations," introducing types of changes, chemical reactions, equations, balancing methods, types of reactions, and concepts like corrosion and rancidity.
Types of Changes
- Physical change: Only physical properties (state, size, shape) change; no new substance is formed.
- Chemical change: Chemical composition changes, resulting in a new substance with different properties.
Chemical Reactions & Equations
- Chemical reaction: Process where substances are transformed into new substances.
- Chemical equation: Symbolic representation of a chemical reaction using formulas and symbols.
- Reactants are written on the left; products on the right.
- Chemical equations must be balanced to follow the Law of Conservation of Mass.
Balancing Chemical Equations
- Number of atoms for each element must be equal on both sides.
- Use coefficients to balance elements one by one.
- PK method: Assign variables, equate atoms, and solve mathematically for complex equations.
Characteristics of Chemical Reactions
- Indications include change in color, temperature, state, evolution of gas, and formation of precipitate.
- Exothermic reaction: Releases heat.
- Endothermic reaction: Absorbs heat.
Types of Chemical Reactions
- Combination Reaction: Two or more reactants form one product (e.g., Mg + O₂ → MgO).
- Decomposition Reaction: One compound breaks into two or more products; can be thermal, electrolytic, or photolytic.
- Displacement Reaction: A more reactive element displaces a less reactive one from a compound.
- Double Displacement Reaction: Exchange of ions between two compounds, often forming a precipitate.
Key Terms & Definitions
- Physical Change — Change in which only physical properties alter; no new substance forms.
- Chemical Change — Change leading to a new substance with new properties.
- Chemical Reaction — Process forming new substances from reactants.
- Chemical Equation — Symbolic depiction of a chemical reaction.
- Reactant/Product — Substances consumed/formed in a reaction.
- Precipitate — Insoluble solid formed in a reaction.
- Exothermic — Reaction that releases heat.
- Endothermic — Reaction that absorbs heat.
- Catalyst — Substance speeding up a reaction without being consumed.
- Redox Reaction — Reaction involving both oxidation and reduction.
- Oxidation — Addition of oxygen or removal of hydrogen.
- Reduction — Addition of hydrogen or removal of oxygen.
- Corrosion — Gradual destruction of metals by chemical reactions.
- Rancidity — Spoiling of fats/oils due to oxidation.
Action Items / Next Steps
- Practice balancing chemical equations using both standard and PK methods.
- Memorize examples and colors for types of reactions, especially for decomposition and displacement.
- Learn reactivity series with mnemonic tricks.
- Revise key terms and practice MCQs.
- Complete all homework questions given in the lecture.
- Prepare for next class by reviewing the notes and solved examples.