Change in molarity

[JulissaLopez1F]

Why is it that for one example on the course reader we had to calculate the change in concentration but for two other examples we assigned the change an concentration an unknown value, "x"?
Do we always say it's "x" or do we calculate in certain instances and if so, what instances?

[Emily_Lenh2A]

Can you please specify which examples in the course reader you are referencing? I'm a bit confused by what you're asking and it might help me (and others) understand what you're asking.

[Aaron_Trell_2J]

Typically we only assign "x" to be a change in molarity. "x" is only used if the information we are given is not enough to calculate certain equilibrium values using the equilibrium constant equations. Typically in these cases we end up using the quadratic formula.