alleryStart learning →When may the change x be neglected against an initial concentration in an equilibrium calculation?
AWhen x is under a tenth of the constant
BWhen x is under a half of the concentration
CWhen the resulting error is under 5 percent
DWhen the constant is smaller than one here
Answer & Solution
Correct answer: C. When the resulting error is under 5 percent
1. Neglecting x turns an awkward quadratic into a simple square root.
2. The move is only allowed when the resulting error stays small.
3. Small is defined as an error of less than 5 percent of the concentration involved.
4. The check is made after solving, by expressing x as a percentage of that concentration.
5. If the figure exceeds 5 percent the assumption fails and the quadratic must be solved.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 13 "Fundamental Equilibrium Concepts", section 13.4 Equilibrium Calculations_
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