GCEChemistryChemical Equilibrium2020

The equilibrium constant expression for the reaction $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$ is

A$K_c = \dfrac{[SO_3]^2}{[SO_2]^2[O_2]}$CORRECT
B$K_c = \dfrac{[SO_2]^2[O_2]}{[SO_3]^2}$
C$K_c = \dfrac{[SO_3]}{[SO_2][O_2]}$
D$K_c = \dfrac{2[SO_3]}{2[SO_2][O_2]}$
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Why the answer is A, and why the others tempt you.
The equilibrium constant expression is written as the product of concentrations of products raised to their stoichiometric coefficients divided by the product of concentrations of reactants raised to their stoichiometric coefficients. For this reaction, $K_c = [SO_3]^2 / ([SO_2]^2[O_2])$. Stoichiometric coefficients appear as exponents, not as multiplying factors.
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