Higher Tier: add a reactant or remove a product
| English | 中文 | Pinyin |
|---|---|---|
| concentration disturbance | 浓度扰动 | nóng dù rǎo dòng |
| re-equilibration | 重新达到平衡 | chóng xīn dá dào píng héng |
What would explain this observation?
- Higher Tier: Removing a product can draw a reversible system toward forming more of it. The response partly replaces what was removed; it does not imply product concentration never fell.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Changing a reactant or product concentration disturbs an equilibrium. Increasing a reactant concentration favours a net forward reaction, consuming some added reactant and forming more products until equilibrium returns. Decreasing a product concentration also favours forward reaction. Increasing a product favours the reverse reaction, while removing a reactant favours reverse formation of that reactant. Use the actual balanced equation to identify each side.
- concentration disturbance 浓度扰动: An imposed change to a reactant or product concentration at equilibrium; re-equilibration 重新达到平衡: Adjustment until forward and reverse reaction rates become equal again.
At fixed temperature, B is removed from A ⇌ B. Which net response is favoured?
Separate the immediate imposed change from the response. If product is removed, its amount first falls; a subsequent net forward change can raise it from that lowered value without necessarily restoring the original level. At the new equilibrium both directions again occur at equal rates. A plot may show a sudden jump in the changed species followed by slower adjustment; the other species need not have the same immediate jump.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Separate the immediate imposed change from the response. If product is removed, its amount first falls; a subsequent net forward change can raise it from that lowered value without necessarily restoring the original level. At the new equilibrium both directions again occur at equal rates. A plot may show a sudden jump in the changed species followed by slower adjustment; the other species need not have the same immediate jump.
- Use original fictional particle or concentration data with a stated fixed temperature and appropriate mixture model. Identify the species directly changed, then predict which direction uses it or replaces it. Real solution mixing can change volume as well as amount, so concentration comparisons need that information. The simple one-to-one particle model is an explanation aid; it is not a numerical equilibrium-constant method.
Which two habits make the investigation or model in this case more defensible?
Use original fictional particle or concentration data with a stated fixed temperature and appropriate mixture model. Identify the species directly changed, then predict which direction uses it or replaces it. Real solution mixing can change volume as well as amount, so concentration comparisons need that information. The simple one-to-one particle model is an explanation aid; it is not a numerical equilibrium-constant method.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: A ⇌ B starts with 40 A and 60 B particles. Removing 20 B immediately leaves 40 A and 40 B. The subsequent response converts a net eight A to B, producing 32 A and 48 B at the supplied new equilibrium. B rose by eight after removal but remains twelve below its original 60. Matter removal was the imposed disturbance; subsequent conversion conserves the remaining total of 80.
A supplied model has 75 B particles, removes 25, then forms a net 12 more during adjustment. Find final B count. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A supplied model has 75 B particles, removes 25, then forms a net 12 more during adjustment. Find final B count.
The result is 62 particles. Known: A ⇌ B starts with 40 A and 60 B particles. Removing 20 B immediately leaves 40 A and 40 B. The subsequent response converts a net eight A to B, producing 32 A and 48 B at the supplied new equilibrium. B rose by eight after removal but remains twelve below its original 60. Matter removal was the imposed disturbance; subsequent conversion conserves the remaining total of 80.
Check the conclusion and its limits
- Do not claim the product-removal operation itself immediately increases product concentration. A forward shift need not mean the final product amount exceeds its pre-removal value. Adding an unrelated substance is not automatically the same as adding a reactant. This whole section is Higher-only and requires qualitative interpretation, not memorised K calculations.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Removing a product means its amount never decreases. This claim is false: Do not claim the product-removal operation itself immediately increases product concentration. A forward shift need not mean the final product amount exceeds its pre-removal value. Adding an unrelated substance is not automatically the same as adding a reactant. This whole section is Higher-only and requires qualitative interpretation, not memorised K calculations.
Higher Tier: add a reactant or remove a product: Separate the immediate imposed change from the response. If product is removed, its amount first falls; a subsequent net forward change can raise it from that lowered value without necessarily restoring the original level. At the new equilibrium both directions again occur at equal rates. A plot may show a sudden jump in the changed species followed by slower adjustment; the other species need not have the same immediate jump.
Removing a product means its amount never decreases.
Do not claim the product-removal operation itself immediately increases product concentration. A forward shift need not mean the final product amount exceeds its pre-removal value. Adding an unrelated substance is not automatically the same as adding a reactant. This whole section is Higher-only and requires qualitative interpretation, not memorised K calculations.
An imposed change to a reactant or product concentration at equilibrium: write the technical term.
concentration disturbance means An imposed change to a reactant or product concentration at equilibrium.