Summary: Class 10 Science Chapter 1 (Chemical Reactions and Equations)
Introduction
- Chemical Reactions: Chemical reactions are fundamental processes where one or more reactants undergo transformation to produce new substances known as products. These changes involve rearrangements of molecular structures and altering the physical and chemical properties of the substances involved.
- Indicators of Chemical Reactions:
- Transition in Physical State: Includes changes such as solid to liquid, liquid to gas, or vice versa, depending on the nature of the reaction.
- Alteration in Colour: Change in colour signifies a chemical alteration. For ex: formation of a new compound.
- Emission of Gaseous Products: Many reactions result in the evolution of gases, confirmed by effervescence or bubbling.
- Fluctuations in Thermal Energy: Exothermic reactions release heat, while endothermic reactions absorb heat, indicating energy transfer within the system.
1.1 Chemical Equations
- Definition: Chemical equations are symbolic representations of chemical reactions, using elemental symbols and molecular formulas to describe reactants and products succinctly.
- Word Equations: Describes chemical processes in linguistic terms, such as Magnesium + Oxygen → Magnesium oxide.
- Skeletal Chemical Equations: Representation using chemical symbols, such as Mg + O₂ → MgO, which requires balancing to conform to the Law of Conservation of Mass.
1.1.1 Writing a Chemical Equation
- Reactants and Products: Reactants denote initial substances, and products are the outcome of the chemical transformation.
- Symbols Used:
- "+": Indicates the presence of multiple reactants or products in the reaction.
- "→": Denotes the direction of the reaction, showing the conversion of reactants into products.
1.1.2 Balanced Chemical Equations
- Law of Conservation of Mass:This Principle states that mass remains conserved during chemical reactions, necessitating equal representation of atomic quantities on both sides of the equation.
- Balancing Equations: Systematic adjustments of coefficients to achieve parity between reactants and products, ensuring adherence to stoichiometric principles.
1.1.3 Steps to Balance a Chemical Equation
- Draft the unbalanced equation, listing all reactants and products with their molecular formulas.
- Quantify the number of atoms for each element in the reactants and products.
- Introduce coefficients to equalize the number of atoms for the most complex molecules first.
- Verify the balance and simplify coefficients to their smallest whole-number ratio.
- Reassess the equation to ensure its compliance with mass conservation laws.
1.2 Types of Chemical Reactions
1.2.1 Combination Reaction
- Definition: A process wherein two or more reactants chemically unite to form a singular product.
- Example: Combustion of carbon: C + O₂ → CO₂.
1.2.2 Decomposition Reaction
- Definition: In this a single compound undergoes breakdown into two or more simpler entities under the influence of energy sources such as heat, light, or electricity.
- Example: Electrolysis of water: 2H₂O → 2H₂ + O₂.
1.2.3 Displacement Reaction
- Definition: A reaction wherein a free element replaces another within a compound, reflecting the relative reactivities of the elements involved.
- Example: Reaction of zinc with copper sulfate: Zn + CuSO₄ → ZnSO₄ + Cu.
1.2.4 Double Displacement Reaction
- Definition: These reactions involve an exchange of ions between two reactants, typically yielding a precipitate, gas, or water.
- Example: Sodium sulfate and barium chloride: Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl.
1.2.5 Oxidation and Reduction
- Oxidation: Incorporates the addition of oxygen or removal of hydrogen from a substance.
- Reduction: Conversely, it involves the removal of oxygen or the addition of hydrogen.
- Example: Combustion of methane illustrates both oxidation and reduction: CH₄ + 2O₂ → CO₂ + 2H₂O.
1.3 Effects of Oxidation Reactions in Daily Life
Corrosion
- Definition: Corrosion represents the gradual degradation of metals through oxidative reactions with environmental elements such as moisture and oxygen.
- Example: Rusting of iron: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃. This poses significant challenges in material science and engineering.
- Mitigation: Protective coatings, galvanisation, and use of corrosion inhibitors are critical measures.
Rancidity
- Definition: Rancidity arises from the oxidation of fats and oils in food products, leading to undesirable taste and odor.
- Prevention Methods:
- Antioxidants: Substances like butylated hydroxytoluene (BHT) that inhibit oxidation.
- Airtight Containers: Minimizing oxygen exposure.
- Refrigeration: Slowing down oxidative processes.
Key equations from the chapter are:
- Burning of Magnesium in Air:
- Word Equation: Magnesium + Oxygen → Magnesium oxide
- Chemical Equation: 2Mg + O₂ → 2MgO
- Reaction Between Zinc and Hydrochloric Acid:
- Word Equation: Zinc + Hydrochloric acid → Zinc chloride + Hydrogen
- Chemical Equation: Zn + 2HCl → ZnCl₂ + H₂
- Formation of Iron(III) Oxide and Hydrogen:
- Unbalanced Chemical Equation: Fe + H₂O → Fe₃O₄ + H₂
- Balanced Chemical Equation: 3Fe + 4H₂O → Fe₃O₄ + 4H₂
- Thermite Reaction (Reduction of Iron(III) Oxide by Aluminum):
- Word Equation: Aluminum + Iron(III) oxide → Aluminum oxide + Iron
- Chemical Equation: 2Al + Fe₂O₃ → Al₂O₃ + 2Fe
- Decomposition of Ferrous Sulfate:
- Word Equation: Ferrous sulfate → Ferric oxide + Sulfur dioxide + Sulfur trioxide
- Chemical Equation: 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃
- Decomposition of Lead Nitrate:
- Word Equation: Lead nitrate → Lead oxide + Nitrogen dioxide + Oxygen
- Chemical Equation: 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
- Decomposition of Calcium Carbonate:
- Word Equation: Calcium carbonate → Calcium oxide + Carbon dioxide
- Chemical Equation: CaCO₃ → CaO + CO₂
- Reaction Between Calcium Oxide and Water:
- Word Equation: Calcium oxide + Water → Calcium hydroxide
- Chemical Equation: CaO + H₂O → Ca(OH)₂
- Reaction Between Calcium Hydroxide and Carbon Dioxide:
- Word Equation: Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
- Chemical Equation: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
- Reaction Between Barium Chloride and Sodium Sulfate:
- Word Equation: Barium chloride + Sodium sulfate → Barium sulfate + Sodium chloride
- Chemical Equation: BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl
- Oxidation of Copper to Copper Oxide:
- Word Equation: Copper + Oxygen → Copper oxide
- Chemical Equation: 2Cu + O₂ → 2CuO
- Reduction of Copper Oxide by Hydrogen:
- Word Equation: Copper oxide + Hydrogen → Copper + Water
- Chemical Equation: CuO + H₂ → Cu + H₂O
- Oxidation of Iron:
- Word Equation: Iron + Oxygen + Water → Hydrated iron(III) oxide (Rust)
- Chemical Equation: 4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O
Keywords
- Chemical Reactions
- Reactants
- Products
- Balanced Equation
- Combination Reaction
- Decomposition Reaction
- Displacement Reaction
- Double Displacement Reaction
- Oxidation
- Reduction
- Corrosion
- Rancidity