Reversing a reaction inverts K; multiplying coefficients raises K to that power; adding reactions multiplies their K values.
Practise Kinetics & Equilibrium All Kinetics & Equilibrium topics
The equilibrium constant changes in predictable ways when a chemical equation is altered. Reversing a reaction gives the reciprocal of K, because the expression is inverted. Multiplying all the coefficients of an equation by a factor n raises K to the power n, since each concentration term appears n times. When two reactions are added to give an overall reaction, their equilibrium constants are multiplied together, a direct consequence of the expression for each step. These rules let chemists combine known equilibria to calculate constants for reactions that have not been measured directly. Such manipulations are routine in solving complex equilibrium problems.
Key ideas: Rules: reverse gives 1/K, multiply coefficients by n gives K^n, add equations gives product of K values, subtract equations gives a quotient. For temperature, these rules apply at the same temperature only. In free energy terms they correspond to adding delta G values, since delta G standard = -RT ln K.
Common mistakes and connections: Students forget to invert for reverse reactions or to take the power for scaled equations. Another is to add K values instead of multiplying them. A mistake also occurs when halving an equation and not taking the square root. Useful for combining Ksp with Kf in complexation and for acid-base constants such as Ka x Kb = Kw. Closely related to Hess's law in thermodynamics.
Adding steps multiplies the K values (2 x 3 = 6) and reversing a reaction inverts K (1/2 = 0.5). The interactive lesson shows this as a live animation or chart.
If one step has K1 = 2 and a second step has K2 = 3, the overall reaction formed by adding them has K = 6.
Reversing a reaction inverts K; multiplying coefficients raises K to that power; adding reactions multiplies their K values.
Manipulating K is a intermediate topic in Kinetics & Equilibrium. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Kinetics & Equilibrium first: Reaction Quotient, Magnitude of K, Homogeneous and Heterogeneous Equilibria.
The next topics in Kinetics & Equilibrium are ICE Tables and Le Chatelier's Principle.
Yes. The interactive lesson includes a self-check question on Manipulating K, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Manipulating K is topic 50 of 91 in Kinetics & Equilibrium.