Equilibrium and changing conditions
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| reversible reaction/rɪˈvɜːsɪbl rɪˈækʃn/ | 可逆反应 | kě nì fǎn yìng |
| equilibrium/ˌiːkwɪˈlɪbrɪəm/ | 平衡 | píng héng |
What would explain this observation?
- A reversible reaction 可逆反应 can continue in a closed vessel while measured concentrations stay constant. Constant composition does not mean particles have stopped reacting.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Dynamic equilibrium 平衡 occurs in a closed system when forward and reverse rates are equal. Reactant and product concentrations are constant, but they need not be equal.
- equilibrium: A state with equal forward and reverse reaction rates; reversible reaction: A reaction that can proceed in both directions.
What is equal at dynamic equilibrium?
Changing conditions can change the equilibrium composition. A catalyst speeds both directions and shortens the time to equilibrium; it does not change the final equilibrium composition at a fixed temperature.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Changing conditions can change the equilibrium composition. A catalyst speeds both directions and shortens the time to equilibrium; it does not change the final equilibrium composition at a fixed temperature.
- State the balanced equation and whether the forward reaction is exothermic before predicting a temperature effect. Count gas coefficients when considering pressure; pressure has no composition effect when gaseous amounts are equal on both sides.
Which two habits make the investigation or model in this case more defensible?
State the balanced equation and whether the forward reaction is exothermic before predicting a temperature effect. Count gas coefficients when considering pressure; pressure has no composition effect when gaseous amounts are equal on both sides.
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 closed system, ten forward reaction events and ten reverse events occur in one second. Net change in the product count = forward events - reverse events = 10 - 10 = 0. The measured composition stays constant while reactions continue.
In one second there are 12 forward events and 12 reverse events. Find the net product-count change. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
In one second there are 12 forward events and 12 reverse events. Find the net product-count change.
The result is 0 . Known: in a closed system, ten forward reaction events and ten reverse events occur in one second. Net change in the product count = forward events - reverse events = 10 - 10 = 0. The measured composition stays constant while reactions continue.
Check the conclusion and its limits
- Do not use a catalyst to claim a larger equilibrium yield. For heterogeneous equilibria, pure solids are omitted from the usual equilibrium expression.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A catalyst changes the equilibrium constant at a fixed temperature. This claim is false: Do not use a catalyst to claim a larger equilibrium yield. For heterogeneous equilibria, pure solids are omitted from the usual equilibrium expression.
Equilibrium and changing conditions: Changing conditions can change the equilibrium composition. A catalyst speeds both directions and shortens the time to equilibrium; it does not change the final equilibrium composition at a fixed temperature.
A catalyst changes the equilibrium constant at a fixed temperature.
Do not use a catalyst to claim a larger equilibrium yield. For heterogeneous equilibria, pure solids are omitted from the usual equilibrium expression.
A state with equal forward and reverse reaction rates: write the technical term.
equilibrium means A state with equal forward and reverse reaction rates.