Stoichiometry & Yield — Investigation · Physical Science: Chemistry, Grade 11
Calculate reacting amounts, identify shortages, and interpret production results.
Limiting-Reactant Production Model
Investigate
How does a shortage change predicted and actual yield?
Use two dedicated sessions: first define the model, boundary, variables and comparison, then collect suitable records or analyze the complete supplied-data route; second complete calculations/graphs, compare alternatives, revise and prepare the report. Extend collection time where needed. Supplied-data work does not certify supervised laboratory minutes or mandated investigations.
Materials
- Paper N₂/H₂ particle cards
- Calculator; supplied production table
Before you begin
Use only the listed household materials or analyze the supplied data. An adult should review setup. No flames, strong acids/alkalis, unknown chemicals, household mains, radiation sources, or high-speed projectiles are needed. Keep food-study materials separate from eating and wash hands afterward.
Plan a fair test
Vary initial reactant amounts; keep equationN₂+3H₂→2NH₃ and the meaning of actual yield fixed.
Method
- Write a prediction and the physical/chemical mechanism behind it.
- Draw the setup or system boundary; label variables and units.
- Calculate ammonia capacity from each reactant independently.
- Choose the smaller capacity and calculate excess remaining.
- Calculate percent yield for each supplied actual amount; compare possible process losses.
- Record repeated observations where possible; keep original readings and note resolution or uncertainty.
- Write a claim supported by specific numbers, explain the mechanism, and identify one limitation and a next test.
Example data — for analysis when materials are unavailable
Illustrative teaching data, not measurements from a real district laboratory. Analyze these when materials are unavailable and identify them as provided data. Do not claim to have performed a measurement you did not make.
| Run | N₂(mol) | H₂(mol) | ActualNH₃(mol) |
|---|---|---|---|
| 1 | 2 | 3 | 1.8 |
| 2 | 2 | 6 | 3.6 |
| 3 | 2 | 9 | 3.5 |
Analyze and explain
- Find theoretical product and limiting reactant for each run.
- Calculate percent yields.
- Can the table identify the specific cause of product loss?
- Link the pattern to a labeled particle, structure, energy or amount model from the chapter.
- Distinguish supplied illustrative records from measurements actually collected.
- Identify uncertainty and propose a comparison that would test an alternative explanation.
What a strong explanation includes
- A stated prediction, conditions, and controlled variables or explicit model boundary.
- A labeled table/graph with units, calculations, and attention to repeated values or uncertainty.
- A claim citing numerical evidence and a scientifically accurate mechanism.
- A limitation, alternative explanation, and useful follow-up test.
- Preserve initial reasoning and an evidence-supported revision.
- Check units, species identity, system boundary and physical assumptions.
Parent / teacher guide: discuss after the investigation
Theoretical yields are 2,4,4 mol. H₂ limits run 1; both are stoichiometric inrun 2; N₂ limits run 3. Yields 90%,90%,87.5%. Actual shortfall could reflect losses, incomplete conversion, or side reactions; these numbers alone do not identify a cause. Preserve the original observations, intermediate working and a labeled mechanism. Report the relevant boundary and model assumptions, discuss an alternative explanation, and identify the next useful measurement; do not replace unexpected data with the illustrative record.
Compare this model with the learner’s actual evidence. Different measurements can support a different conclusion; check the reasoning and limitations, not matching wording.