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Yes, I agree. The 5% rule states that your amount has to be within this range of the initial concentration, if it is not you will have to solve for the variable using the quadratic formula and you would pick the positive x value that’s within the range.
5% rule is a way you can test if you assume x is so small of a number it is negligible in finding x. for example if Kc= x^2 / (.55-x) you could try the assumption and calculate for x like this Kc=x^2 /(.55). Once you get a value you can test if it is less than 5% of the initial concentration given. If it is less then the assumption holds, if not you have to solve for x the quadratic way.
The 5% rule allows one to ignore the x in the denominator if the equilibrium constant is less than 10^-3 when performing ICE table calculations. The change in concentration (x) must be less than or equal to 5% of the initial concentration. If the change in concentration (x) is greater than 5%, then you cannot ignore the x and must solve a quadratic equation to find the change in concentration (x).
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