2.2 The Meaning of Keq
- Page ID
- 32233
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What can the value of Keq tell us about a reaction?
- If Keq is very large, the concentration of the products is much greater than the concentration of the reactants. The reaction essentially "goes to completion"; all - or most of - of the reactants are used up to form the products.
- If Keq is very small, the concentration of the reactants is much greater than the concentration of the products. The reaction does not occur to any great extent - most of the reactants remain unchanged, and there are few products produced.
- When Keq is not very large or very small (close to a value of 1) then roughly equal amounts of reactants and products are present at equilibrium.
Here are some examples to consider:
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the decomposition | \(\ce{2O_3(g) \leftrightarrow 3O_2(g)}\) | \(\mathrm{K_{eq}=2.0 \times 10^{57}}\) |
Keq is very large, indicating that mostly O2 is present in an equilibrium system, with very little O3 | ||
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production of nitrogen monoxide | \(\ce{N_2(g) + O_2(g) \leftrightarrow 2NO(g)}\) | \(\mathrm{K_{eq}=1.0 \times 10^{-25}}\) |
Very little NO is produced by this reaction; N2 and O2 do not react readily to produce NO (lucky for us - otherwise we would have little oxygen to breath in our atmosphere!) | ||
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reaction of carbon monoxide and water | \(\ce{CO(g) + H_2O(g) \leftrightarrow CO_2(g) + H_2(g)}\) | \(\mathrm{K_{eq}=5.09}\) (at 700 K) |
The concentrations of the reactants are very close to the concentrations of the products at equilibrium |