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### Course: AP®︎/College Chemistry>Unit 7

Lesson 4: Magnitude and properties of the equilibrium constant

# Magnitude of the equilibrium constant

The magnitude of the equilibrium constant provides information about the relative amounts of reactants and products at equilibrium. A large K value (greater than 1) indicates that there are more products than reactants at equilibrium, while a small K value (less than 1) indicates that there are more reactants than products at equilibrium. Created by Jay.

## Want to join the conversation?

• At , what does Jay mean by "relatively close to 1?" Wouldn't there be more products than reactants at equilibrium because 51 is greater than 1?
• True, but it's way closer than a million, and HI would be squared, so it's more like 7 to 1 which is comparable.
• Say you have the hypothetical reaction: A ⇌ 2B
'Kc' would equal ([B]^2)/[A]. So far so good. However, in the video, Jay says that when k<1 there are more reactants than products at equilibrium. And vice versa for k>1. If there was, say, 10 B particles and 10 A particles at equilibrium, the result of the equation be (([B]^2)/[A]) would be 10. If kc equals 10, it is supposed to meant that the reaction favors products over reactants since k>1. Though since there is 10 particles of each, this doesn't make sense since there is the same amount of products and reactants in my hypothetical equilibrium.
To sum it up, it seems to me that the introduction of powers make the k<1 and k>1 rules not work all the time, could someone clear this up for me? Thank you so much!
• Most reactions have more than one chemical species for the products and reactants, and have coefficients greater than 1 so the equilibrium constant is really a measure of the ratio of the products of the numerator and denominator, not simply their individual concentrations. So a K>1 really means that the numerator product (of the products in the actual reaction) is larger than the product of the denominator (the reactants). And so usually this also means that the concentrations of the products are greater than that of the reactants, but that isn’t always the case as you’ve discovered.

For your example reaction, if K = 10, with [B] = 10 M and [A] = 10 M, then the numerator product is indeed larger than the denominator even though the individual concentrations are the same, [B]^(2) > [A], but [B] = [A]. You can stretch this even farther by making [B] = 20 M. K still remains 10 which means [A] will have to be 40 M. So again the numerator product is larger than the denominator by a factor of 10, but this time the individual reactant concentration is greater than the individual product concentration, [B]^(2) > [A], but [B] < [A]. We can also go in a different direction where [B] > [A]. If K = 10 and [B] = 5, then [A] = 2.5. This is possible too because the important part is that [B]^(2) > [A]. There are an infinite range of values for [A] and [B], so long as the equilibrium expression equals 10.

If K>1 then the numerator product is larger, and if K<1 then the denominator product is larger. The individual concentrations need not necessarily be larger or smaller in every instance because the equilibrium expression is a quotient of products reliant in stoichiometric coefficients.

Hope that helps.