Safety boundary
Use paper models, supplied data, and approved simulations only. No unsupervised reactive mixtures are required.
Explicit chemistry instruction
A balanced equation preserves atom counts and provides proportional mole relationships among substances.
Coefficients become conversion factors such as 2 mol H₂ per 1 mol O₂. They do not directly describe gram ratios.
Choose the ratio that cancels the starting substance and leaves the target substance.
Vocabulary: stoichiometric ratio; coefficient; mole ratio; reactant; product.
Worked example
For 2H₂ + O₂ → 2H₂O, 3.0 mol O₂ corresponds to 6.0 mol H₂O if H₂ is available in excess.
Guided question
A balanced equation gives 2A + 3B → 4C. How many moles C form from 1.5 mol B with excess A?
Independent work
- Write three mole-ratio conversion factors from one equation.
- Solve three mole-to-mole problems.
- Explain why an unbalanced equation cannot support valid stoichiometry.
Misconception check
Coefficients are mole ratios, not subscripts and not direct mass ratios.
Formative check
What must be done before using an equation for stoichiometry?
Reveal response
Balance it.
Mentor evidence conference
Ask Archaemenes to audit units, conversion factors, equation coefficients, and model assumptions.
Teacher guidance
Foundation: Highlight coefficients and build ratios.
Core: Solve mole-to-mole conversions.
Extended: Compare multiple valid paths and check atom conservation.