Chemistry · 40 minutes
Suggested grades 10–11 · Unit 3: Rates and Dynamic Equilibrium · Lesson 2 of 2
More Product Does Not Mean the Reaction Stopped
Distinguish equilibrium position from reaction speed using a reversible-system model.
Mr. S Teaches · Original starter lesson · HS-CHEM-06 · Grade range is planning guidance.Watch, notice, discuss
Video choices for this lesson
Preview a video, then choose what fits your learners. “Show to class” opens a larger view; use the player’s play and full-screen controls when you’re ready.
Teacher preview needed. Check the language, level and length before showing. YouTube may show ads or related videos.
Equilibrium: Crash Course Chemistry #28
By CrashCourse
Use the forward/reverse-rate distinction to explain why a stable mixture is still reacting, then evaluate a system change.
Open on YouTube: Equilibrium: Crash Course Chemistry #28 (opens a new tab) ↗What is chemical equilibrium? - George Zaidan and Charles Morton
By TED-Ed
Compare the collision analogy with dynamic equilibrium; identify where an everyday analogy stops matching molecular behavior.
Open on YouTube: What is chemical equilibrium? - George Zaidan and Charles Morton (opens a new tab) ↗What idea from the video helps you recommend and justify one system change that increases product while explaining dynamic equilibrium? Identify one useful example and one limit of the video's model or explanation.
An external player loads only after you choose Preview or Show to class. Playback connects to YouTube. Videos belong to their creators; availability and embedding can change.
Learning objective
Recommend and justify one system change that increases product while explaining dynamic equilibrium.
Before you begin
- Read a reversible equation and distinguish rate from amount.
Gather your materials
- Paper or notebook
- Pencil; calculator optional for numerical work; all task data supplied below
Language to know
- dynamic equilibrium
- A condition with equal forward and reverse rates and stable macroscopic amounts.
- equilibrium position
- The relative amounts of reactants and products at equilibrium.
- catalyst
- A substance that changes a reaction pathway and speed without changing the equilibrium composition under fixed conditions.
Understand the concept
Paper system: A + B ⇌ C in a sealed idealized vessel. At fixed temperature, a stable mixture has equal forward and reverse rates, not necessarily equal amounts of A, B and C. Removing some C can favor net formation of more C as the system approaches a new equilibrium. Adding a catalyst speeds approach in both directions but does not change the equilibrium position at that temperature. A claim that a catalyst alone doubles the final C amount confuses speed with position.
Teach it step by step
- Read the text and label forward and reverse arrows in a particle-exchange sketch.
- Explain why stable amounts do not imply stopped microscopic reactions.
- Compare removing C with adding a catalyst, stating which change targets composition and which targets approach speed.
- Refine a product-increasing proposal and name a practical constraint omitted by the paper model.
Make the thinking visible
Worked example or model response
If forward and reverse rates are each 5 model events/s, net C change is zero even though events continue. A catalyst could make both rates 10 events/s at the same equilibrium composition; “zero net” is not “zero activity.”
Guided practice
Together critique “Equilibrium requires one-third each A, B and C.” Use the distinction between equal rates and equal quantities.
Independent practice
Write a recommendation for increasing C by a specified system change. Compare an alternate catalyst proposal, explain its limitation and identify a constraint such as cost or continuous product separation.
Quick assessment
Would adding a catalyst by itself change the fixed-temperature equilibrium amounts in this model?
Answer key & assessment criteria
Answers and teaching guidance
- Guided: Equal forward/reverse rates do not require equal quantities; the stated one-third conclusion is unsupported.
- Independent: A supported proposal removes C or adds a reactant under the model, explains a net response and distinguishes catalyst effects; practical constraints must be explicit.
- Quick check: No. It changes how rapidly equilibrium is approached rather than the equilibrium position at fixed temperature.
Look for: Assess the stated objective using the concrete criteria and explanations in the answer key. Invite an alternative supported solution; distinguish a model’s prediction from an established observation.
Make it work for your learner
More support
Use paired forward/reverse event counters to separate rate from total amount.
Extension challenge
Explain why a real industrial decision must balance equilibrium yield, approach speed, energy, separation and safety rather than maximizing one variable.
Verified references · Selected contributions
Standards connections
Selected NGSS high school-band contribution; full performance requires additional evidence and instruction.
Subject-content standards
These records identify the part of a subject standard practiced here. Course placement is instructional guidance; the source’s category or band remains authoritative.
Contributes to NGSS performance expectation
HS-PS1-6
NGSS · High school band
Refine a system change that increases product at equilibrium.
Read the official performance expectation ↗This selected reversible-system proposal considers one composition change and a catalyst comparison. It does not construct or test a real equilibrium system or evaluate all industrial conditions.
Verified 2026-11-04. Selected contribution, not full attainment.
Supporting literacy connections
These records apply to the specified reading, writing or communication task. They do not establish subject-content alignment.
Supporting Common Core literacy connection
RST.9-10.1
Common Core · Grades 9–10
Use precise textual details in scientific analysis.
Read the official standard ↗The activity explicitly analyzes the provided technical text, table or model. It contributes selected literacy practice rather than complete grade-band reading coverage or independent subject-content alignment.
Verified 2026-11-04. Selected contribution, not full attainment.