What is the equilibrium expression for the following acid dissociation reaction?
CH3COOH + H2O CH3COO- + H3O+
A. [CH3COO-][H3O+]/[CH3COOH][H3O]
B. [CH3COOH][H2O]/[CH3COO-][H3O+]
C. [CH3COOH]/[CH3COO-][H3O-]
D. [CH3COO-][H3O+]/[CH3COOH]
To determine the equilibrium expression for the given acid dissociation reaction, we need to express the concentrations (or activities) of the reactants and products.
The general form of the equilibrium expression for a reaction of the form:
aA + bB → cC + dD
is:
K = [C]^c[D]^d / [A]^a[B]^b
In the given acid dissociation reaction, CH3COOH is the acid (A), H2O is the solvent (B), CH3COO- is the conjugate base (C), and H3O+ is the hydronium ion (D).
Therefore, the correct equilibrium expression is:
K = [CH3COO-][H3O+] / [CH3COOH][H2O]
Looking at the options provided:
A. [CH3COO-][H3O+]/[CH3COOH][H3O]
This option includes an extra [H3O] term in the denominator, which is incorrect.
B. [CH3COOH][H2O]/[CH3COO-][H3O+]
This option correctly represents the equilibrium expression for the acid dissociation reaction.
Hence, the correct answer is B.
C. [CH3COOH]/[CH3COO-][H3O-]
This option incorrectly includes [H3O-], which is not a product of this acid dissociation reaction.
D. [CH3COO-][H3O+]/[CH3COOH]
This option is missing the [H2O] term from the denominator, which is incorrect.
Therefore, the correct equilibrium expression for the given acid dissociation reaction is option B: [CH3COOH][H2O]/[CH3COO-][H3O+].