Chemical Reactions and Equations

Introduction

• The lecture aims to comprehensively cover the "Chemical Reactions and Equations" chapter.
• The approach includes concept explanations, practice questions, and addressing competency-based and case-based questions.
• Following the lecture and practicing the provided questions should be enough to score high marks without needing external coaching.

Prerequisites and Resources

• The lecture is suitable for students following the NCERT syllabus, regardless of their specific board (CBSE, ICSE, SSC, etc.).
• Class notes will be available on the Telegram channel.

Changes: Physical vs. Chemical

• Before diving into chemical reactions, it's essential to understand changes, broadly categorized into physical and chemical.

Physical Change

• Physical changes don't involve chemical reactions.
• Example: Tearing paper is a physical change, altering form without changing chemical composition.
• Burning a candle is a mix: burning is chemical (oxygen involvement), melting wax is physical.
• Examples of physical changes: chopping vegetables, boiling water, a sponge absorbing water.

Chemical Change

• Chemical changes involve chemical reactions.
• Examples:
  • Combustion or burning of a candle (the flame).
  • Ripening fruits involves reactions with moisture and oxygen.
  • Respiration, unlike breathing, involves breaking down food with oxygen to form glucose.

Defining Chemical Reaction

• Involves interaction of chemicals to form new chemicals
• Example: Water formation, where H2 and O2 react to form H2O.

Components of a Chemical Reaction

• Reactants: Chemical substances that interact/collide before a reaction.
• Products: Substances formed after the reaction.

Conditions Affecting Chemical Reactions

• Heat, sunlight, or pressure can influence reactions.
  • Example: Silver Bromide (AgBr) breaks down into Ag and Br2 when exposed to sunlight.

Gas Liberation

• Some reactions result in gas release.
  • Example: Calcium Carbonate (CaCO3) when heated, breaks down into CaO and Carbon Dioxide (CO2) gas.

Catalysts

• Alter the rate of a reaction.
• Catalysts aren't consumed in the reaction.

Precipitate Formation

• A precipitate forms in a reaction when a solid is produced.
• Example: pb(NO3)2 (aq) + 2NaI (aq) -> PbI2 (s) - PbI2 is the precipitate.

Change in Physical State

• Reactions can cause a change of state.
• Two gases can combine to create a liquid.

Types of Chemical Reactions

• Combination Reaction: Two/more reactants combine to form a single product

  • H2 + O2 → H2O
  • C + O2 → CO2

• Decomposition Reaction: A single reactant breaks down into two or more products.

  • caco3 -> CaO + CO2

Types of Decomposition Reaction

• Thermal Decomposition: Breakdown due to heat

• Electrolytic Decomposition: Breakdown from electric current.

  • H2O -> Hydrogen+Oxygen

• Photo-chemical Decomposition- Breakdown due to sunlight

• Displacement Reaction: A more reactive element displaces a less reactive one from a compound.

  • Example: CuSO4 + Zn → ZnSO4 + Cu (Zn takes SO4, displacing Cu)

• Double Displacement Reaction: Involves an exchange of ions between two reactants.

  • Example: BaCl+Na2,SO4 -> NaCl+BaSO4

Reactions Based on Energy Flow

• Endothermic Reactions: Require energy(heat) to be supplied.

  • Example: CaCO3 --> CaO + CO2

• Exothermic Reactions: Release Energy

  • Example: CH4 + O2 → CO2 + H2O + Energy

Redox Reactions

• Involve both Reduction and Oxidation taking place simultaneously.

Reduction

• Oxygen removal
• Hydrogen addition
• Addition of electrons
• Example: Cu²⁺ + 2e⁻ → Cu (Reduction - electrons added)

Oxidation

• Oxygen addition
• Hydrogen removal
• Electrons removal
• Example: Zn° → Zn²⁺ + 2e⁻ (Oxidation - electrons removed)

Relationship of Reduction/Oxidation w/ Agents

• Reducing Agent: Substance causing reduction (it oxidizes)
• Oxidizing Agent: Substance causing oxidation (it reduces)
• MnO₂ + 4 HCl → MnCl₂ + 2 H₂O + Cl₂
• Oxidizing agent: MnO₂
• Reducing agent: HCl

Corrosion

• Deterioration of a metal in reaction to its environment.
• Iron + Oxygen gives Hydrated Iron Oxide (rust).

Prevention of Corrosion

• Painting
• Greasing
• Galvanization

Corrosion in Copper

• Copper + Water + CO2-> Copper Carbonate
• Copper Carbonate turns things blue/green

Corrosion in Silver

• Silver + Sulfur -> Silver Sulfide
• Turns things Black

Rancidity

• Oxidation of fat/oil in food produces a bad smell.
• Prevented by:
  • Air-tight container
  • Adding antioxidants
  • Using nitrogen gas

Balancing Chemical Reactions

• Balancing equations ensures the same number of atoms on each side.
• Balance equations by trying random multipliers until reaching equality.

Activities

• Quicklime + Water -> Sleaked Lime
• Causes Heat be Produced: exothermic

Activity: Zinc Granules Conical Flask

• Zinc metal + Dilute acids -> Hydrogen gas

Lead Nitrate + Potassium Iodide -> Lead Iodide (precipitate) (s) + potassium Nitrate (aq)

• Double displacement
• Solid Form is Precipitation: PbI2 (s)

Copper Powder Being Heated

• Copper+Heat-> copper oxide
  • Copper oxide is black
• Cu+H2-> Copper again, as long as you displace the hydrogen

End note

• There might be hard times, but remember, others judge/hate you either way.