Magnitude of the Equilibrium Constant
Introduced| English | Meaning |
|---|---|
| position of equilibrium/pəˈzɪʃn ɒv ˌiːkwɪˈlɪbrɪəm/ | The relative amounts of reactants and products present when forward and reverse reaction rates are equal. |
How big is big?
- The size of that one number tells a whole story.
- A huge value means the reaction nearly finishes.
- A tiny value means it barely gets started.
- One glance at the number reveals which side wins.
A large K favours products
- A large $K$ (much greater than 1) means products dominate.
- The reaction goes almost to completion.
- At equilibrium there is lots of product and little reactant.
A large K means mostly products at equilibrium; a small K means mostly reactants
A large $K$ (much greater than 1) means the equilibrium favours...
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Large $K$ means the reaction nearly goes to completion -- product-favoured.
The larger $K$ is, the more the equilibrium favours the ____.
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A bigger $K$ means more product at equilibrium.
A small K favours reactants
- A small $K$ (much less than 1) means reactants dominate.
- The reaction barely proceeds.
- At equilibrium there is lots of reactant and little product.
A small $K$ (much less than 1) means the equilibrium favours...
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Small $K$ means the reaction barely proceeds -- reactant-favoured.
K around 1
- When $K \approx 1$, products and reactants are comparable.
- Neither side strongly wins.
- The position of equilibrium 平衡位置 sits in the middle.
What does K's size tell you?
Match the size of K to the make-up of the equilibrium mixture.
If $K \approx 1$, then at equilibrium...
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Near 1 means significant amounts of both sides.
Reaction A has $K = 10^6$; reaction B has $K = 10^{-6}$. Which favours products?
- A's huge $K$ means products dominate.
- B's tiny $K$ means it stays mostly reactants.
A large $K$ means the reaction reaches equilibrium quickly.
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$K$ shows the position, not the speed; speed is kinetics.
The value of $K$ stays the same at every temperature.
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False. $K$ is temperature-dependent; changing the temperature is the only way to change $K$ for a given reaction.
$K$ tells you the position of equilibrium (which side is favoured), not how fast it is reached — that is kinetics. Large $K$ is product-favoured, small $K$ is reactant-favoured. And $K$ is temperature-dependent: change the temperature and $K$ changes.
The magnitude of $K$ sets the position of equilibrium: a large $K$ (much bigger than 1) favours products, a small $K$ (much less than 1) favours reactants, and $K \approx 1$ means both are comparable. $K$ describes the balance, not the speed of reaching it.