Інтерпретація величини $K_eq$

We've been learning about equilibrium. We started by studying reversible chemical reactions. Next, we learned that a system is in chemical equilibrium when the forward reaction's rate equals the reverse reaction's rate. But, remember the reactant and product concentrations can be very different. It is only the rates that are equivalent!

For equilibrium reactions, we can define a constant. We creatively call it the equilibrium constant. It's the quotient of the rate laws for the forward and reverse reactions. But, remember we assume that each reaction is an elementary step.

Maybe you're asking, "what does $K_{eq}$ tell me?" Today we'll interpret the equilibrium constant. By looking at the constant's magnitude, we can make qualitative predictions.

Magnitude of $K_{eq}$

The size of the equilibrium constant tells us about our reaction. Remember, its formula is $K_{eq}=\frac{[Product]}{[Reactants]}=\frac{[C]^{c}[D]^{d}}{[A]^{a}[B]^{b}}$. The product concentration is in the numerator. So, if $K_{eq}$ is large, the reaction must lean towards the products. If $K_{eq}$ is small, it must favor the reactants.

• $K_{eq} >> 1$

• The numerator is larger.

• The reaction favors the products. The products' concentrations are much greater than the reactants'.

• $K_{eq} << 1$

• The denominator is larger.

• The equilibrium favors the reactants. The reactants' concentrations are much greater than the products'.

• $K_{eq} \approx 1$

• The numerator and denominator are about equal.

• The reactants' and products' concentrations are about equal. The reaction does not favor one side.

Comparing $Q$ to $K_{eq}$

If our reaction is not in equilibrium, use $Q$, the reaction quotient. Remember, its formula is the same as the equilibrium constant. It's $Q=\frac{[Product]}{[Reactants]}=\frac{[C]^{c}[D]^{d}}{[A]^{a}[B]^{b}}$. We can compare the equilibrium constant to the reaction quotient. That will tell us which way our reaction shifts to equilibrate.

• $Q < K_{eq}$

• The reaction favors the reactants' side.

• The forward reaction will dominate. Reactants will convert to products to reach equilibrium.

• The forward reaction's rate will exceed the reverse reaction's rate until equilibrium.

• $Q > K_{eq}$

• The reaction favors the products' side.

• The reverse reaction will dominate. Products will convert to reactants to achieve equilibrium.

• The reverse reaction's rate will exceed the forward reaction's rate.

• $Q = K_{eq}$

• The reaction is at equilibrium.

(Video) Interpreting Magnitude of Keq: The Equilibrium Constant

By Bozeman Science

In this video, Paul Andersen reminds you how to calculate the equilibrium constant. Generally, the equilibrium constant is a ratio of the concentration of the products to the concentration of the reactants. When the equilibrium constant is greater than one, the reaction moves from the left side to the right, and the product is favored. On the other hand, if the equilibrium constant is less than one, the reaction moves from the right to the left, and the reactant is favored.

Interpreting magnitude of Keq: What does the magnitude of equilibrium constant tells us?