Rates & Equilibrium — Investigation · Physical Science: Chemistry, Grade 11
Distinguish reaction speed from equilibrium composition and calculate direction of adjustment.
Rates versus Equilibrium Evidence
Investigate
Can a catalyst change the time to reach a result without changing its final ratio?
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
- Provided reaction-model tables
- Calculator andgraphs
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
Compare with/without catalyst at fixed temperature and initial amounts; use reversibleA⇌B withK=3.
Method
- Write a prediction and the physical/chemical mechanism behind it.
- Draw the setup or system boundary; label variables and units.
- Plot B concentration versus time for both trials.
- Compare early slopes and finalB/A ratios.
- CalculateQ at an intermediate time and predict direction; identify a control for temperature.
- 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.
| Time(s) | B uncatalyzed(M) | B catalyzed(M) |
|---|---|---|
| 0 | 0 | 0 |
| 10 | 0.2 | 0.6 |
| 30 | 0.55 | 0.74 |
| 100 | 0.75 | 0.75 |
Analyze and explain
- Compare early average production rates.
- Find equilibriumA andK for total 1.00M.
- What measurement would test an apparent different final composition?
- 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
Early B rates are.020 and.060M/s. Both approachB=.75,A=.25 soK=3. Catalyst affects rate, not this equilibrium. Check temperature, waiting time, side reactions, and measurement calibration before interpreting a different final ratio. 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.