alleryStart learning →Pure reactants alone are mixed in a flask. What is the value of Qc at that instant?
AQc = 0, since no product is present yet
BQc = 1, since the ratio starts balanced
CQc is infinite, since products are absent
DQc equals Kc, since the flask is sealed
Answer & Solution
Correct answer: A. Qc = 0, since no product is present yet
1. The numerator of Qc holds the product concentrations, each raised to its coefficient.
2. With pure reactants only, every product concentration is zero, so the numerator is zero.
3. A zero numerator over a non zero denominator gives Qc = 0.
4. Qc then rises as products build, and stops changing only once equilibrium is reached.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 13 "Fundamental Equilibrium Concepts", section 13.2 Equilibrium Constants_
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