Zinc nitrate has the formula Zn(NO₃)₂. When zinc nitrate is heated, it decomposes to form zinc oxide, nitrogen dioxide and oxygen. The word equation for this reaction is: zinc nitrate → zinc oxide + nitrogen dioxide + oxygen. Write the balanced symbol equation for this reaction, showing all state symbols at room temperature. The formula for nitrogen dioxide is NO₂ and the formula for zinc oxide is ZnO.

Pearson Edexcel International GCSE Chemistry (4CH1) — 1.5 Chemical formulae, equations and calculations · State · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

2Zn(NO₃)₂(s) → 2ZnO(s) + 4NO₂(g) + O₂(g)

Use the command word ‘State’ – write the full balanced equation, not just the formulae.
Include state symbols for all species; solid for Zn(NO₃)₂ and ZnO, gas for NO₂ and O₂.
Check coefficients – double the reactant to balance the oxygen atoms.
Remember to write the formula for nitrogen dioxide as NO₂, not N₂O₄.

Leaving out state symbols or using (l) instead of (s) for solids.
Using the wrong coefficient for Zn(NO₃)₂, e.g. 1 instead of 2, leading to an unbalanced equation.
Writing NO₂ as N₂O₄ or omitting the oxygen atoms in the products.