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Year 10 - Science

Balancing equations

Calculations involving masses

Unit Summary

This unit covers writing chemical formulae, balancing equations, and using the conservation of mass. It includes calculating moles, empirical formulae, relative formula masses, and theoretical yields. Emphasis is on stoichiometry, concentration, gas volumes, and using standard form.

Lesson Summary

You will learn to balance chemical equations, and explain why it is important to ensure symbol equations are balanced.

Key Notes

  • All the atoms in the reactants of a chemical reaction are reorganised to form all the products of the reaction.
  • There must be an equal number of each type of atom on both the reactant and product side of the equation.
  • Chemical formulae cannot be altered to balance a reaction equation; only coefficients can change.
  • Atoms cannot be created or destroyed. During a chemical reaction, atoms are simply rearranged into products.

Vocabulary To Learn

  • word equation: A word equation represents a chemical reaction using the chemical names of the reactants and products.
  • chemical formula: A chemical formula represents a substance using element symbols and the number / ratio of atoms of each element in the substance.
  • symbol equation: A symbol equation represents a chemical reaction using the chemical formulas of the reactants and products.
  • balanced symbol equation: A balanced symbol equation uses coefficients to ensure that the number of atoms of each element is equal on both sides of the equation.
  • coefficient: A coefficient is the number placed in front of a chemical formula to balance an equation; it multiplies all the atoms in the formula and shows the ratio of substances in a reaction.

Common Mistakes To Avoid

  • Pupils sometimes think that chemical formulae can be changed to balance atoms.

3 Quick Questions (With Answers)

1. Explain the scientific idea in this lesson using two key points.

All the atoms in the reactants of a chemical reaction are reorganised to form all the products of the reaction. There must be an equal number of each type of atom on both the reactant and product side of the equation.

2. Define this scientific word and use it in context. 'word equation'

A word equation represents a chemical reaction using the chemical names of the reactants and products. Include the word in a full scientific explanation, not as a single label.

3. Correct this common scientific misunderstanding.

Mistake: Pupils sometimes think that chemical formulae can be changed to balance atoms. Correction: Put boxes around each formula in the equation / pretend there is a bucket of pre-made molecules which they can use to balance the number of atoms on each side. Stress that it takes perseverance and practice before equations are balanced.

More Lessons In This Unit

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