Higher Tier: warming favours the endothermic direction
| English | 中文 | Pinyin |
|---|---|---|
| endothermic direction | 吸热方向 | xī rè fāng xiàng |
| exothermic direction | 放热方向 | fàng rè fāng xiàng |
What would explain this observation?
- Higher Tier: Heating can make reactions faster yet reduce the equilibrium amount of a desired product. Rate and final equilibrium composition need separate explanations.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Increasing temperature favours the endothermic direction 吸热方向, which takes in energy and counteracts warming. Decreasing temperature favours the exothermic direction 放热方向, which releases energy. If the written forward reaction is endothermic, warming increases the relative product amount and cooling decreases it. If forward is exothermic, warming decreases relative products and cooling increases them. Always state which direction the given energy label describes.
- endothermic direction: The reaction direction taking energy from the surroundings; exothermic direction: The reaction direction transferring energy to the surroundings.
The written forward reaction is exothermic. What is the equilibrium response to warming?
Both forward and reverse reactions can become faster on warming, yet their relative rate balance changes, causing a net shift before a new equilibrium is reached. For an exothermic forward industrial reaction, a low temperature may favour yield while slowing production; an appropriate temperature choice can be a compromise. A catalyst can help rate without turning that exothermic forward direction into an endothermic one or increasing its equilibrium yield at fixed conditions.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Both forward and reverse reactions can become faster on warming, yet their relative rate balance changes, causing a net shift before a new equilibrium is reached. For an exothermic forward industrial reaction, a low temperature may favour yield while slowing production; an appropriate temperature choice can be a compromise. A catalyst can help rate without turning that exothermic forward direction into an endothermic one or increasing its equilibrium yield at fixed conditions.
- Read a supplied equation and mark forward endothermic/exothermic before writing a shift conclusion. Use data collected after equilibrium at each stated temperature, with other relevant conditions specified. A temporary product increase during heating is not necessarily the final equilibrium composition. This lesson predicts direction and evaluates supplied evidence; no numerical equilibrium constant or thermodynamic derivation is required.
Which two habits make the investigation or model in this case more defensible?
Read a supplied equation and mark forward endothermic/exothermic before writing a shift conclusion. Use data collected after equilibrium at each stated temperature, with other relevant conditions specified. A temporary product increase during heating is not necessarily the final equilibrium composition. This lesson predicts direction and evaluates supplied evidence; no numerical equilibrium constant or thermodynamic derivation is required.
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: in a fictional exothermic A ⇌ B mixture at equilibrium, the supplied product fraction is 70% at a lower temperature and 55% at a higher one. Warming favours the reverse endothermic direction, consistent with the 15 percentage-point decrease. In a stated total of 200 represented particles, product counts are 140 and 110; the decrease is 30. These numbers are illustrative, not actual chemical yield data.
A supplied product fraction falls from 64% to 49% on warming. Find the decrease in percentage points. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A supplied product fraction falls from 64% to 49% on warming. Find the decrease in percentage points.
The result is 15 percentage points. Known: in a fictional exothermic A ⇌ B mixture at equilibrium, the supplied product fraction is 70% at a lower temperature and 55% at a higher one. Warming favours the reverse endothermic direction, consistent with the 15 percentage-point decrease. In a stated total of 200 represented particles, product counts are 140 and 110; the decrease is 30. These numbers are illustrative, not actual chemical yield data.
Check the conclusion and its limits
- Do not write heating always increases equilibrium yield. The term exothermic must attach to a direction, not to the reversible pair without qualification. Percentage-point change is not the same as percentage change relative to the original value. A faster approach to equilibrium does not prove a more product-rich equilibrium.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Heating always increases the equilibrium proportion of products. This claim is false: Do not write heating always increases equilibrium yield. The term exothermic must attach to a direction, not to the reversible pair without qualification. Percentage-point change is not the same as percentage change relative to the original value. A faster approach to equilibrium does not prove a more product-rich equilibrium.
Higher Tier: warming favours the endothermic direction: Both forward and reverse reactions can become faster on warming, yet their relative rate balance changes, causing a net shift before a new equilibrium is reached. For an exothermic forward industrial reaction, a low temperature may favour yield while slowing production; an appropriate temperature choice can be a compromise. A catalyst can help rate without turning that exothermic forward direction into an endothermic one or increasing its equilibrium yield at fixed conditions.
Heating always increases the equilibrium proportion of products.
Do not write heating always increases equilibrium yield. The term exothermic must attach to a direction, not to the reversible pair without qualification. Percentage-point change is not the same as percentage change relative to the original value. A faster approach to equilibrium does not prove a more product-rich equilibrium.
The reaction direction taking energy from the surroundings: write the technical term.
endothermic direction means The reaction direction taking energy from the surroundings.