Higher Tier: count gaseous coefficients before predicting a shift
導入済み| English | 意味 |
|---|---|
| compression/kəmˈpreʃn/ | 圧縮 |
| gas-coefficient count/ɡæs ˌkəʊɪˈfɪʃənt kaʊnt/ | 気体係数計数 |
What would explain this observation?
- Higher Tier: Compressing an equilibrium gas mixture favours the side with fewer gaseous particles. Count coefficients from the balanced equation before naming the favoured product.
Build the model
- For gaseous equilibria, increasing pressure by compression 压缩 at fixed temperature shifts toward the side with fewer gas molecules in the balanced equation.
- Decreasing pressure by expansion favours the side with more gas molecules.
- Count gaseous coefficients, not every atom inside each formula.
- For N₂(g) + 3H₂(g) ⇌ 2NH₃(g), the left side has four gas molecules to the right side’s two, so compression favours ammonia.
- gas-coefficient count 气体系数计数: The sum of balanced equation coefficients for gaseous species on one side.
- compression: Reducing the volume of a stated gas mixture to raise its pressure at fixed temperature.
For N₂(g) + 3H₂(g) ⇌ 2NH₃(g), compression at fixed temperature favours which side?
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
Compression favours the side with FEWER gas molecules. Here 1 + 3 = 4 reactant molecules become only 2 ammonia molecules, so higher pressure shifts towards ammonia. Atom balance is irrelevant to the gas-count rule.
Match each technical term to its precise meaning.
難易度 2/5 · 140 コイン + 今日初回完了時に小ボーナス付与
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- If the gas-molecule counts are equal on both sides, changing pressure by compression gives no pressure-driven composition shift in this model.
- H₂(g) + I₂(g) ⇌ 2HI(g) has two on each side.
- If solids or liquids occur in a supplied equation, do not count their coefficients as gas molecules.
- Compression can also affect rates by increasing gas particle concentration; a rate effect alone is not proof of an equilibrium shift.
In the lab: Write state symbols and a gas-count total under each side. Specify compression or expansion of the reacting mixture at constant temperature: merely adding an unrelated gas does not justify blindly applying the same rule without a volume/pressure description. Evaluate a supplied industrial choice using yield, rate, equipment cost and operating constraints. Do not ask students to construct high-pressure reaction vessels.
Which two habits make the investigation or model in this case more defensible?
難易度 2/5 · 140 コイン + 今日初回完了時に小ボーナス付与
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: in 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), gas coefficients total three on the left and two on the right.
- Compression favours the product side; expansion favours reactants.
- One thousand represented stoichiometric forward sets convert 3,000 gas molecules into 2,000, a decrease of 1,000 in this counting model.
- The equation count predicts shift direction, not a specific percentage conversion.
Your turn: For N₂ + 3H₂ ⇌ 2NH₃ with all species gaseous, find the total gaseous coefficient count on the reactant side.
For N₂ + 3H₂ ⇌ 2NH₃ with all species gaseous, find the total gaseous coefficient count on the reactant side.
難易度 2/5 · 140 コイン + 今日初回完了時に小ボーナス付与
The result is 4 . Known: N2 + 3H2 on the reactant side, both gaseous. Total gaseous coefficients = 1 + 3 = 4. The product side has 2, so compression favours the products.
Check the conclusion and its limits
- Do not count oxygen atoms to decide the gas-count rule.
- A higher pressure does not always favour products; it favours the smaller gaseous count.
- Equal counts mean no pressure-driven shift under the stipulated compression model, not that rate can never change.
- This entire source section is Higher-only.
Not true: Increasing pressure always shifts equilibrium toward the products. Pressure shifts equilibrium toward the side with fewer GAS molecules - whichever side that is. If the products had more gas molecules, pressure would favour the reactants; equal counts mean no shift at all.
- For gaseous equilibria, increasing pressure by compression at fixed temperature shifts toward the side with fewer gas molecules in the balanced equation.
- If the gas-molecule counts are equal on both sides, changing pressure by compression gives no pressure-driven composition shift in this model.
- Watch for: do not count oxygen atoms to decide the gas-count rule.
Pressure shifts equilibrium toward the side with fewer GAS molecules - whichever side that is.
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
True. Pressure shifts equilibrium toward the side with fewer GAS molecules - whichever side that is. If the products had more gas molecules, pressure would favour the reactants; equal counts mean no shift at all.
The sum of balanced equation coefficients for gaseous species on one side: write the technical term.
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
gas-coefficient count means The sum of balanced equation coefficients for gaseous species on one side.