GCSE Combined Science (AQA)

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Using Moles to Balance Equations

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Quantitative chemistry Use of amount of substance in relation to masses of pure substances

Using Moles to Balance Equations

11:53 Moles, Mass, and Balanced Equations
Spec 4.3.2.3
Previous Moles Next Factors Affecting Concentration
  • Chemical equations can be interpreted in terms of moles.
  • Balanced equations indicate the moles of reactants and products.
  • Example: Magnesium reacts with hydrochloric acid to produce magnesium chloride and hydrogen.
  • Multipliers in equations represent moles and ensure conservation of mass.
  • For magnesium and hydrochloric acid reaction, 2 moles of hydrochloric acid are needed for 1 mole of magnesium.
  • Balancing numbers in equations can be calculated from masses of reactants and products.
  • Example: Hydrogen and oxygen react to produce water; masses are converted to moles.
  • Moles are calculated using the formula: Moles = Mass in grams / Relative formula mass.
  • Simplify mole ratios to whole numbers for balancing equations.
  • Example: Copper reacts with oxygen to form copper oxide; use given masses to balance the equation.
  • Use periodic table to find MR values for compounds.
  • Calculate moles for each reactant and product, then simplify the ratio.
  • If ratios are not whole numbers, multiply to convert to whole numbers.
  • Example: Iron reacts with oxygen to form iron oxide; balance using mole ratios.
  • Ensure balanced equations have equal atoms on both sides.

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