Science, Tech, Math › Science Equilibrium Constant Definition Share Flipboard Email Print The equilibrium constant is a ratio based on equilibrium concentrations. Rafe Swan, Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated March 08, 2019 The equilibrium constant is the ratio of the equilibrium concentrations of the products raised to the power of their stoichiometric coefficients to the equilibrium concentrations of the reactants raised to the power of their stoichiometric coefficients.For a reversible reaction:aA + bB → cC + dDThe equilibrium constant, K, is equal to:K = [C]c·[D]d/[A]a·[B]bwhere[A] = equilibrium concentration of A[B] = equilibrium concentration of B[C] = equilibrium concentration of C[D] = equilibrium concentration of D There are several different types of equilibrium constants. These including binding constants, association constants, dissocation constants, stability constants, and formation constants. Factors that may affect the equilibrium constant include temperature, ionic strength, and choice of solvent. Source Denbigh, K. (1981). "Chapter 4". The Principles of Chemical Equilibrium (4th ed.). Cambridge: Cambridge University Press. ISBN 978-0-521-28150-8.