Chemical Reactions, FORMULAE and Equations

• Word Equation


  Describes a chemical reaction using the names of the reactants and products
• Balanced Chemical Equation


  Uses chemical symbols and formulas to represent a chemical reaction, with the same number of each type of atom on both sides to obey the Law of Conservation of Mass
• Steps to Balance an Equation

  1. Write the unbalanced equation with correct formulas

  2. Count the number of atoms of each element on both sides

  3. Add coefficients to balance the atoms

  4. Check that all elements are balanced and the coefficients are in the simplest ratio
• State Symbols


  • (s) = solid
  • (l) = liquid
  • (g) = gas
  • (aq) = aqueous solution
• Combustion of Methane


  • Word equation: Methane + Oxygen → Carbon Dioxide + Water
  • Balanced chemical equation: CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
• Formation of Sodium Chloride

  • Word equation: Sodium + Chlorine → Sodium Chloride
  • Balanced chemical equation: 2Na(s) + Cl2(g) → 2NaCl(s)
• Neutralization Reaction


  • Word equation: Hydrochloric Acid + Sodium Hydroxide → Sodium Chloride + Water
  • Balanced chemical equation: HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
• Relative Atomic Mass (Ar)


  The weighted average mass of an atom of an element compared to one-twelfth of the mass of a carbon-12 atom
• Relative Formula Mass (Mr)


  The sum of the relative atomic masses of all atoms in a chemical formula
• Steps to Calculate Mr

  1. Write down the chemical formula

  2. Identify the Ar for each element

  3. Multiply the Ar of each element by the number of atoms

  4. Add the total masses for all elements
• Calculating Mr


  • Water (H2O): Mr = (2 x 1) + (1 x 16) = 18
  • Carbon Dioxide (CO2): Mr = (1 x 12) + (2 x 16) = 44
  • Calcium Carbonate (CaCO3): Mr = (1 x 40) + (1 x 12) + (3 x 16) = 100
• Combustion


  A chemical reaction where a substance reacts with oxygen, releasing energy in the form of light and heat
• Combustion of Magnesium


  • Word Equation: Magnesium + Oxygen → Magnesium Oxide
  • Balanced Chemical Equation: 2Mg(s) + O2(g) → 2MgO(s)
  • Observation: Bright white light, white powder (magnesium oxide) is formed
• Combustion of Hydrogen


  • Word Equation: Hydrogen + Oxygen → Water
  • Balanced Chemical Equation: 2H2(g) + O2(g) → 2H2O(l)
  • Observation: Colourless flame, water (as steam) is formed
• Combustion of Sulfur


  • Word Equation: Sulfur + Oxygen → Sulfur Dioxide
  • Balanced Chemical Equation: S(s) + O2(g) → SO2(g)
  • Observation: Blue flame, pungent smell of sulfur dioxide gas
• Thermal Decomposition


  The breakdown of a chemical compound into simpler substances when heated
• Thermal Decomposition of Copper(II) Carbonate

  • Word Equation: Copper(II) Carbonate → Copper(II) Oxide + Carbon Dioxide
  • Balanced Chemical Equation: CuCO3(s) → CuO(s) + CO2(g)
  • Observation: The green copper(II) carbonate turns into black copper(II) oxide, and carbon dioxide gas is released
• General Pattern for Metal Carbonates

  Most metal carbonates decompose upon heating to form a metal oxide and carbon dioxide
• Thermal Decomposition of Calcium Carbonate


  • Word Equation: Calcium Carbonate → Calcium Oxide + Carbon Dioxide
  • Balanced Chemical Equation: CaCO3(s) → CaO(s) + CO2(g)
  • Observation: The white calcium carbonate turns into white calcium oxide, and carbon dioxide gas is released
• Thermal Decomposition of Zinc Carbonate

  • Word Equation: Zinc Carbonate → Zinc Oxide + Carbon Dioxide
  • Balanced Chemical Equation: ZnCO3(s) → ZnO(s) + CO2(g)
  • Observation: The white zinc carbonate turns into yellow (when hot) zinc oxide, and carbon dioxide gas is released
• Reaction of Acids with Metals

  Acids react with metals to produce a salt and hydrogen gas
• Reaction of Hydrochloric Acid with Zinc


  • Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
  • Observation: Bubbles of hydrogen gas are produced
• Reaction of Sulfuric Acid with Magnesium

  • Mg(s) + H2SO4(aq) → MgSO4(aq) + H2(g)
  • Observation: Bubbles of hydrogen gas are produced
• Reaction of Acids with Bases

  Acids react with bases to produce a salt and water (neutralization reaction)
• Reaction of Hydrochloric Acid with Sodium Hydroxide

  • HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
  • Observation: No visible change, but the temperature of the solution may increase
• Reaction of Sulfuric Acid with Copper(II) Oxide


  • H2SO4(aq) + CuO(s) → CuSO4(aq) + H2O(l)
  • Observation: The black copper oxide dissolves to form a blue solution of copper(II) sulfate
• Example Reaction with Magnesium (Mg)

  Mg(s)+H2SO4(aq)→MgSO4(aq)+H2(g)
• Observation: Bubbles of hydrogen gas are produced
• Reactions with Bases (Metal Oxides and Hydroxides)

  Acid+Base→Salt+Water
• Example Reaction with Sodium Hydroxide (NaOH)

  HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l)
• Observation: No visible change, but the temperature of the solution may increase
• Example Reaction with Copper(II) Oxide (CuO)


  H2SO4(aq)+CuO(s)→CuSO4(aq)+H2O(l)
• Observation: The black copper oxide dissolves to form a blue solution of copper(II) sulfate
• Example Reaction with Sodium Hydroxide (NaOH)

  HNO3(aq)+NaOH(aq)→NaNO3(aq)+H2O(l)
• Reactions with Metal Carbonates

  Acid+Metal Carbonate→Salt+Water+Carbon Dioxide
• Example Reaction with Calcium Carbonate (CaCO3)


  CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g)
• Observation: Bubbles of carbon dioxide gas are produced, and the solid carbonate dissolves
• Example Reaction with Zinc Carbonate (ZnCO3)


  ZnCO3(s)+H2SO4(aq)→ZnSO4(aq)+H2O(l)+CO2(g)
• Example Reaction with Sodium Carbonate (Na2CO3)

  Na2CO3(s)+2HNO3(aq)→2NaNO3(aq)+H2O(l)+CO2(g)
• Hydrogen (H2)


  Pop Test: The gas will ignite with a distinctive 'pop' sound