Work Step by Step
$[I_2]=0.0088\ M(1-78.6/100)=0.00188\ M=[H_2]$ $[HI]=2\times0.0088\ M\times78.6/100=0.0138\ M$ $K_c=[HI]^2/[H_2][I_2]$ $K_c=53.9$
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