Chemistry Question

[Daniel Brim]

Alright, I guess I'll make an example.

In the system of acetic acid (HC₂H₃O₂<----> H⁺ + C₂H₃O₂^-), K_a=1.8x10^-5. If [HC₂H₃O₂] = [H⁺] = [C₂H₃O₂^-] = 1.0 M

a. Find Q
b. Predict which direction the reaction will shift in order to reach equilibrium

a. First, write the K_a expression, which will be
[H⁺][C₂H₃O₂^-]
[HC₂H₃O₂]

The expression will be the same as the K_a expression. So Q also equals
[H⁺][C₂H₃O₂^-]
[HC₂H₃O₂]

Plug in the values for concentrations given. This gives you (1x1)/1.

Q=1

b. Since Q>K_a, the amount of products is too high (you can think of this as having to make Q smaller until it reaches K_a). Therefore, the reaction needs to shift to the reverse reaction until Q=K_a


The same thing can be done with K_c and K_p in gaseous systems.

Does this help?