chemical reactions and equations

• Milk left at room temperature during summers undergoes a chemical change
• An iron tawa/pan/nail left exposed to humid atmosphere undergoes a chemical change
• Grapes getting fermented is an example of a chemical change
• Food being cooked involves a chemical change
• Food getting digested in our body is a chemical change
• Respiration is a chemical change
• Chemical reactions occur when a chemical change takes place
• Observations that help determine a chemical reaction has taken place include:

  • Change in state
  • Change in color
  • Evolution of a gas
  • Change in temperature
• Chemical equations represent chemical reactions
• A word-equation for burning magnesium in oxygen is:

  Magnesium + Oxygen → Magnesium oxide
• A chemical equation for the burning of magnesium in air is:

  Mg + O2 → MgO
• Balanced chemical equations are necessary to follow the law of conservation of mass
• Balancing a chemical equation involves ensuring the number of atoms of each element is the same on both sides of the equation
• A chemical equation for the reaction between zinc and sulfuric acid is:

  Zn + H2SO4 → ZnSO4 + H2
• Balancing a chemical equation for Fe + H2O → Fe3O4 + H2 involves:

  • Ensuring the number of atoms of each element is the same on both sides
  • Adding coefficients to balance the equation
• Physical states of reactants and products can be represented in a chemical equation using (s), (l), (aq), and (g)
• An example of a balanced chemical equation with physical states included is:

  3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
• Chemical reactions involve breaking and making bonds between atoms to produce new substances
• Types of chemical reactions include:

  • Combination Reaction
• An example of a combination reaction is the formation of slaked lime by adding water to calcium oxide
• Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat
• In the reaction CaO(s) + H2O(l) → Ca(OH)2(aq), calcium oxide and water combine to form calcium hydroxide
• This reaction is a combination reaction, where a single product is formed from two reactants
• Combination reactions occur when two or more substances combine to form a single product
• Exothermic reactions release heat along with the formation of products
• Examples of exothermic reactions include the burning of natural gas and respiration
• Decomposition reactions involve a single reactant breaking down to give simpler products
• Thermal decomposition reactions occur when a decomposition reaction is carried out by heating
• An example of a thermal decomposition reaction is the decomposition of calcium carbonate to calcium oxide and carbon dioxide
• Displacement reactions involve one element displacing another in a compound
• Examples of displacement reactions include Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s) and Pb(s) + CuCl2(aq) → PbCl2(aq) + Cu(s)
• Double displacement reactions involve the exchange of ions between two compounds
• In a double displacement reaction between sodium sulphate and barium chloride, barium sulphate and sodium chloride are formed
• When mixing sodium sulfate (Na2SO4) and barium chloride (BaCl2) solutions, a white insoluble substance, known as a precipitate, is formed
• A precipitation reaction occurs when a reaction produces a precipitate
• In the reaction between Na2SO4(aq) and BaCl2(aq), BaSO4(s) (barium sulfate) and 2NaCl(aq) (sodium chloride) are formed
• During the oxidation of copper to copper oxide (CuO), oxygen is added to copper to form the black copper(II) oxide coating
• In the reaction CuO + H2 → Cu + H2O, copper(II) oxide is reduced as it loses oxygen, while hydrogen is oxidised as it gains oxygen
• Redox reactions involve oxidation and reduction, where one reactant gets oxidised and the other gets reduced
• Corrosion is the process where metals like iron are attacked by substances like moisture and acids, leading to damage