Consider the general reversible reaction.

Lower A upper A plus lower B upper B double-headed arrow lower C upper C plus Lower d upper D.

What is the equilibrium constant expression for the given system?
K e q equals StartFraction lowercase C StartBracket upper C EndBracket lowercase d StartBracket upper D EndBracket over lowercase A StartBracket upper A EndBracket lowercase B StartBracket upper B EndBracket EndFraction.
K e q equals StartFraction StartBracket upper C EndBracket StartBracket upper D EndBracket over StartBracket upper A EndBracket StartBracket upper B EndBracket EndFraction.
K e q equals StartFraction StartBracket upper A EndBracket superscript lower a StartBracket upper B EndBracket superscript lower b over StartBracket upper C EndBracket superscript lower c StartBracket upper D EndBracket superscript lower D EndFraction.
K e q equals StartFraction StartBracket upper C EndBracket superscript lower c StartBracket upper D EndBracket superscript lower D over StartBracket upper A EndBracket superscript lower a StartBracket upper B EndBracket superscript lower b EndFraction.