GCSE CHEMISTRY / BALANCING EQUATIONS / INDEPENDENT SUPPLEMENT
YOUR STARTING POINT
Balance the atoms.
Keep the formulae.
GCSE chemistry method summary + practice
Learn a repeatable way to balance supplied chemical equations, then make your answer prove itself with
an atom audit. This is a focused paper-and-pencil guide for learners who can recognise element symbols
but lose track of coefficients, brackets or oxygen atoms.
24 original practice tasks 3 worked demonstrations
Counting and notation, guided equations, error repair and A separate answer section explains the decisions and
mixed practice checks every element
One rule to carry through every page
Keep the formula of each supplied substance fixed. Put a multiplier in front of it to change the amount
represented. After each change, revisit every element affected by that multiplier.
A quick diagnostic
In 3CO2, the leading 3 applies to the entire formula. It represents three C atoms and six O atoms. Writing
CO6 instead changes the formula; it does not express three copies of carbon dioxide.
Route through the guide
Page 2: counting and coefficient rules. Page 3: two worked demonstrations. Page 4: brackets, strategy and
the final audit. Pages 5-10: six practice sets. Pages 11-16: explained solutions. Page 17: repair log, precise
scope and references.
How to practise
Complete a set before looking at its solutions. Write your coefficients, count every element on both sides,
then check the smallest whole-number ratio. Use extra paper when needed. Return to any failed task after
a break and explain the repaired method aloud.
Independent resource | Version 1.0 | 17 September 2026
Created with AI assistance. Formula counts and coefficients checked by code; pages visually reviewed. No independent expert
review, school attendance, grade or exam outcome is claimed. Not affiliated with or endorsed by AQA. These are original study
tasks, not past-paper or live-assignment answers.
Version 1.0 | September 2026 | Original balancing practice 1
,GCSE CHEMISTRY / BALANCING EQUATIONS / INDEPENDENT SUPPLEMENT
METHOD SUMMARY
Read the numbers
in the right order.
Subscript: inside one formula
CO contains one C and two O per molecule. An omitted subscript is 1. Changing the subscript changes
2
the formula, so it is not a balancing operation.
Bracket multiplier: every element in the group
Mg(OH)2 contains Mg = 1, O = 2 and H = 2 per formula unit. The outside 2 multiplies the OH group only. It
does not reach back to Mg.
Coefficient: every atom in the formula
2Mg(OH)2 represents Mg = 2, O = 4 and H = 4. Multiply the complete formula count by the coefficient. Do
not add the coefficient to a subscript.
Expression How to read it Atom count
CO2 One carbon dioxide molecule C1; O2
3CO2 Three carbon dioxide molecules C3; O6
Mg(OH)2 One magnesium hydroxide formula unit Mg1; O2; H2
2Mg(OH)2 Two formula units Mg2; O4; H4
What does balanced mean?
Each element has the same total count on both sides of the arrow. Equal total atoms alone is not enough:
oxygen cannot stand in for hydrogen. The number of molecules need not be equal. The arrow separates
reactants from products; plus signs separate substances on the same side.
Two finishing checks
Conservation: do all element counts match? Ratio: do the positive whole-number coefficients share a
common factor? If so, divide every coefficient by that factor. A coefficient of 1 is usually left unwritten.
These tasks ask for the smallest whole-number ratio.
Version 1.0 | September 2026 | Original balancing practice 2
, GCSE CHEMISTRY / BALANCING EQUATIONS / INDEPENDENT SUPPLEMENT
WORKED DEMONSTRATIONS A AND B
Make one change.
Recount its effects.
A short coefficient audit
___ K + ___ Cl → ___ KCl
2
Begin with K + Cl → KCl. The chlorine counts are 2 versus 1. Put 2 before KCl, then 2 before K. The
2
coefficient 1 before Cl2 is normally omitted.
Balanced: 2 K + Cl2 → 2 KCl
Element Reactant atoms Product atoms
Cl 2 2
K 2 2
Use a common atom count
___ Al + ___ O2 → ___ Al2O3
The oxygen subscripts 2 and 3 meet at 6. Write 3O2 and 2Al2O3. The product now contains four Al atoms,
so place 4 before Al. Recheck both elements after the last edit.
Balanced: 4 Al + 3 O2 → 2 Al2O3
Element Reactant atoms Product atoms
Al 4 4
O 6 6
Why rechecking matters
When the product coefficient changes, every atom in that product changes with it. In demonstration B, fixing
the oxygen count also changes the aluminium count. An earlier match may need to be repaired.
A balanced equation specifies relative amounts. It does not mean that the two sides contain equal numbers of molecules or
equal numbers of written formulae.
Version 1.0 | September 2026 | Original balancing practice 3
YOUR STARTING POINT
Balance the atoms.
Keep the formulae.
GCSE chemistry method summary + practice
Learn a repeatable way to balance supplied chemical equations, then make your answer prove itself with
an atom audit. This is a focused paper-and-pencil guide for learners who can recognise element symbols
but lose track of coefficients, brackets or oxygen atoms.
24 original practice tasks 3 worked demonstrations
Counting and notation, guided equations, error repair and A separate answer section explains the decisions and
mixed practice checks every element
One rule to carry through every page
Keep the formula of each supplied substance fixed. Put a multiplier in front of it to change the amount
represented. After each change, revisit every element affected by that multiplier.
A quick diagnostic
In 3CO2, the leading 3 applies to the entire formula. It represents three C atoms and six O atoms. Writing
CO6 instead changes the formula; it does not express three copies of carbon dioxide.
Route through the guide
Page 2: counting and coefficient rules. Page 3: two worked demonstrations. Page 4: brackets, strategy and
the final audit. Pages 5-10: six practice sets. Pages 11-16: explained solutions. Page 17: repair log, precise
scope and references.
How to practise
Complete a set before looking at its solutions. Write your coefficients, count every element on both sides,
then check the smallest whole-number ratio. Use extra paper when needed. Return to any failed task after
a break and explain the repaired method aloud.
Independent resource | Version 1.0 | 17 September 2026
Created with AI assistance. Formula counts and coefficients checked by code; pages visually reviewed. No independent expert
review, school attendance, grade or exam outcome is claimed. Not affiliated with or endorsed by AQA. These are original study
tasks, not past-paper or live-assignment answers.
Version 1.0 | September 2026 | Original balancing practice 1
,GCSE CHEMISTRY / BALANCING EQUATIONS / INDEPENDENT SUPPLEMENT
METHOD SUMMARY
Read the numbers
in the right order.
Subscript: inside one formula
CO contains one C and two O per molecule. An omitted subscript is 1. Changing the subscript changes
2
the formula, so it is not a balancing operation.
Bracket multiplier: every element in the group
Mg(OH)2 contains Mg = 1, O = 2 and H = 2 per formula unit. The outside 2 multiplies the OH group only. It
does not reach back to Mg.
Coefficient: every atom in the formula
2Mg(OH)2 represents Mg = 2, O = 4 and H = 4. Multiply the complete formula count by the coefficient. Do
not add the coefficient to a subscript.
Expression How to read it Atom count
CO2 One carbon dioxide molecule C1; O2
3CO2 Three carbon dioxide molecules C3; O6
Mg(OH)2 One magnesium hydroxide formula unit Mg1; O2; H2
2Mg(OH)2 Two formula units Mg2; O4; H4
What does balanced mean?
Each element has the same total count on both sides of the arrow. Equal total atoms alone is not enough:
oxygen cannot stand in for hydrogen. The number of molecules need not be equal. The arrow separates
reactants from products; plus signs separate substances on the same side.
Two finishing checks
Conservation: do all element counts match? Ratio: do the positive whole-number coefficients share a
common factor? If so, divide every coefficient by that factor. A coefficient of 1 is usually left unwritten.
These tasks ask for the smallest whole-number ratio.
Version 1.0 | September 2026 | Original balancing practice 2
, GCSE CHEMISTRY / BALANCING EQUATIONS / INDEPENDENT SUPPLEMENT
WORKED DEMONSTRATIONS A AND B
Make one change.
Recount its effects.
A short coefficient audit
___ K + ___ Cl → ___ KCl
2
Begin with K + Cl → KCl. The chlorine counts are 2 versus 1. Put 2 before KCl, then 2 before K. The
2
coefficient 1 before Cl2 is normally omitted.
Balanced: 2 K + Cl2 → 2 KCl
Element Reactant atoms Product atoms
Cl 2 2
K 2 2
Use a common atom count
___ Al + ___ O2 → ___ Al2O3
The oxygen subscripts 2 and 3 meet at 6. Write 3O2 and 2Al2O3. The product now contains four Al atoms,
so place 4 before Al. Recheck both elements after the last edit.
Balanced: 4 Al + 3 O2 → 2 Al2O3
Element Reactant atoms Product atoms
Al 4 4
O 6 6
Why rechecking matters
When the product coefficient changes, every atom in that product changes with it. In demonstration B, fixing
the oxygen count also changes the aluminium count. An earlier match may need to be repaired.
A balanced equation specifies relative amounts. It does not mean that the two sides contain equal numbers of molecules or
equal numbers of written formulae.
Version 1.0 | September 2026 | Original balancing practice 3
