Class 10 CBSE SCIENCE

• Chemical reaction is the process in which new substances with new properties are formed from one or more substances
• Examples of chemical reactions include:

  • Process of respiration
  • Rusting of iron
  • Burning of magnesium ribbon
• Reactants are the substances that take part in a chemical reaction
• Products are the new substances formed as a result of a chemical reaction
• Magnesium ribbon should be cleaned before burning in air to remove the protective layer of magnesium oxide from its surface so that it may readily combine with the oxygen of air on heating
• Examples of chemical reactions characterized by:

  • Evolution of gas: Reaction between zinc and dilute sulphuric acid
  • Change in colour: Reaction between lead nitrate solution and potassium iodide solution
  • Formation of precipitate: Action of barium chloride on sodium sulphate
  • Change in temperature: Action of dilute sulphuric acid on zinc
  • Change in state: Burning of wax in the form of a wax candle
• Chemical equations are balanced to satisfy the law of conservation of mass in chemical reactions
• Steps involved in balancing a chemical equation:

  • Write the word equation
  • Write the chemical equation
  • Count the number of atoms of each element on both sides
  • Balance the equation by multiplying the molecules as needed
• A chemical equation can be made more informative by mentioning physical states of the substances involved, heat changes involved in the reaction, and conditions under which the reaction takes place
• Types of chemical reactions include:

  • Combination reactions
  • Decomposition reactions
  • Displacement reactions
  • Double displacement reactions
  • Redox reactions
• Decomposition reactions involve a single reactant breaking down into two or more simpler products
• Decomposition reactions are carried out by applying heat, light, or electricity
• Decomposition reactions are the opposite of combination reactions
• Example: CaCO3(s) → CaO(s) + CO2(g) (limestone breaks down into lime and carbon dioxide)
• Thermal decomposition, photolytic decomposition, and electrolytic decomposition are types of decomposition reactions
• Endothermic reactions absorb energy (heat, light, or electricity)
• Displacement reactions involve a more reactive element displacing a less reactive element from its salt solution
• Example: Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) (Iron displaces copper from copper sulfate solution)
• Reactivity series arranges metals in decreasing order of reactivity
• Metals higher in the reactivity series can displace metals lower in the series from their salt solutions
• Double displacement reactions involve an exchange of ions between reactants
• Example: Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq) (forms a white precipitate, BaSO4)
• Redox reactions involve both oxidation and reduction
• Oxidation reactions involve adding oxygen or removing hydrogen from a substance
• Reduction reactions involve removing oxygen or adding hydrogen to a substance
• In a redox reaction, the substance oxidized is the reducing agent and the substance reduced is the oxidizing agent
• Effects of oxidation reactions in everyday life include corrosion and rancidity
• Corrosion is the gradual deterioration of a material, like metal, by moisture, air, or chemicals
• Rusting is a type of corrosion where iron reacts with oxygen and moisture to form rust
• Rancidity is the oxidation of fats and oils in food, causing foul smell and bad taste
• Prevention methods for rancidity include using air-tight containers, refrigeration, and adding antioxidants