Dynamic equilibrium
Introduced| English | Meaning |
|---|---|
| reversible reaction/rɪˈvɜːsɪbl rɪˈækʃn/ | A reaction whose products can react to form the original reactants under suitable conditions. |
| closed system/kləʊzd ˈsɪstəm/ | A system that does not exchange matter with its surroundings, although energy may be transferred. |
| dynamic equilibrium/daɪˈnæmɪk ˌiːkwɪˈlɪbrɪəm/ | A state in which opposing processes continue at equal rates, so there is no overall change in composition. |
| macroscopic/ˌmækrəˈskɒpɪk/ | Describing properties or observations at a scale involving bulk matter rather than individual atoms or molecules. |
Reactions that never finish
- A reversible reaction 可逆反应 can go both ways ($\rightleftharpoons$).
- In a closed system 封闭系统 it reaches a dynamic equilibrium 动态平衡.
- At equilibrium nothing appears to change — but both reactions are still going.
A reversible reaction is one that:
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A reversible reaction (⇌) can form products and turn them back into reactants.
A closed system is needed to reach equilibrium.
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If the system were open, products could escape and the forward and reverse rates could never balance.
At dynamic equilibrium the forward and backward reactions have both stopped.
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False. Both reactions continue at equal rates, which is why it is called dynamic. Concentrations stay constant because the rates balance.
What equilibrium means
- At dynamic equilibrium:
- the forward rate equals the reverse rate, and
- the concentrations of reactants and products stay constant.
- It is dynamic because both reactions are still happening — they just cancel out.
- A closed system is needed, or products would escape and equilibrium could never be reached.
Dynamic equilibrium
forward rate = reverse rate
At equilibrium the position can sit anywhere — change a condition and watch it shift.
At dynamic equilibrium:
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The two rates are equal, so the concentrations of reactants and products no longer change.
Why is it called a "dynamic" equilibrium?
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Both forward and reverse reactions continue at equal rates, so they balance — dynamic, not static.
The features of equilibrium
- Equilibrium is only reached in a closed system.
- The macroscopic 宏观 properties (concentration, colour) stay constant once equilibrium is reached.
Cobalt chloride changes colour as its equilibrium shifts
Match each equilibrium term to its meaning.
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Each item links the term to its correct meaning.
A common misconception
- At equilibrium the amounts of reactants and products are constant, but not necessarily equal.
- The position of equilibrium can lie far to one side.
You've got it
- a reversible reaction ($\rightleftharpoons$) goes both ways
- dynamic equilibrium: forward rate = reverse rate, concentrations constant
- both reactions still happen (dynamic); needs a closed system