Le Chatelier's principle
Introduced| English | Meaning |
|---|---|
| Le Chatelier's principle/lə ˈtʃeɪtlɪəz ˈprɪnsɪpl/ | If you change a system at equilibrium , it shifts to oppose the change. |
| equilibrium/ˌiːkwɪˈlɪbrɪəm/ | A state with no resultant force or resultant moment. |
| catalyst/ˈkætəlɪst/ | A substance that increases a reaction rate without being used up overall. |
| endothermic/ˌendəʊˈθɜːmɪk/ | Describing a process that takes in heat from its surroundings. |
Nudging a balance
- Le Chatelier's principle 勒夏特列原理: if you change a system at equilibrium 平衡, it shifts to oppose the change.
- This predicts which way the equilibrium moves.
- A catalyst 催化剂 is the exception — it shifts nothing.
Le Chatelier's principle says that a change to a system at equilibrium causes it to:
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The equilibrium position always moves in the direction that lessens the change you made.
Increasing the pressure shifts equilibrium towards the side with more gas molecules.
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False. By Le Chatelier's principle, higher pressure shifts equilibrium towards the side with fewer gas molecules, which reduces the pressure.
The changes
| Change | Equilibrium moves |
|---|---|
| increase a reactant's concentration | towards products |
| increase pressure | towards the side with fewer gas molecules |
| increase temperature | towards the endothermic 吸热 direction |
Le Chatelier's principle: the equilibrium shifts to oppose the change you make
Le Chatelier's principle
the system opposes the change
Raise T, P or reactant and the equilibrium shifts to oppose your change.
Increasing the pressure shifts the equilibrium towards:
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Moving to fewer gas molecules reduces the pressure, opposing the increase.
Increasing the temperature shifts the equilibrium towards:
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The endothermic direction absorbs the added heat, opposing the temperature rise.
Catalysts
- A catalyst speeds up both the forward and reverse reactions equally.
- So equilibrium is reached faster, but its position does not change.
Adding a catalyst to a system at equilibrium:
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A catalyst speeds up both directions equally, so the position of equilibrium is unchanged.
Match each change to how the equilibrium responds.
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Each item links the term to its correct meaning.
Temperature and the catalyst
- Raising temperature shifts equilibrium in the endothermic direction.
- A catalyst speeds up both directions equally, so it does not shift the position.
You've got it
- Le Chatelier: the equilibrium shifts to oppose any change you make
- more reactant → towards products; more pressure → fewer-gas-molecules side; more heat → endothermic direction
- a catalyst speeds both ways equally → reaches equilibrium faster, no shift