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2.1.1—Chemical equations

Syllabus
First assessment 2025
Objective
2.1.1
Level
HL

Balanced Chemical Equations

A balanced chemical equation conserves every element and charge. Its coefficients show the mole ratio of reactants and products.

Write the products and state symbols, balance atoms with coefficients rather than changing formula subscripts, then check every element and the charge.

For Al + O₂ → Al₂O₃, preserve the formulas and choose coefficients 4Al + 3O₂ → 2Al₂O₃. Changing O₂ to O or Al₂O₃ to another subscript would change the substances rather than balance them. Add state symbols from chemical evidence or stated conditions, not from atom counting.

Balancing with State Symbols

Assessment in practice

Representative question

Question 1

[Maximum number: 2]

Write an equation for the reaction, including all state symbols.

Amount of Chemical Change Summary

Retrieve the route: balance the equation, convert through the coefficient mole ratio, identify the limiting reactant, calculate theoretical and percentage yield, then assess atom economy.

Check formula subscripts, state symbols, ratio direction, units, the smallest normalized reactant amount, the theoretical-yield denominator, and the total reactant mass used for atom economy.