Intermediate Topic 467 of 1102 Kinetics & Equilibrium
Magnitude of K
Large K favours products, small K favours reactants.
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In-depth explanation of Magnitude of K
The magnitude of the equilibrium constant indicates how far a reaction proceeds before equilibrium is reached. A value much greater than one, roughly above 10^3, means that the reaction goes essentially to completion and products dominate. A value much smaller than one, roughly below 10^-3, means that very little product forms and reactants remain nearly unchanged. Intermediate values produce appreciable concentrations of both reactants and products at equilibrium. The size of K says nothing about how fast the reaction proceeds, because a reaction with a very large K may still be extremely slow. Thermodynamics determines K, while kinetics determines how quickly equilibrium is reached.
Going deeper: Magnitude of K
Key ideas: Quick guide: K above 10^3 means reaction is essentially complete, K below 10^-3 means almost no reaction, and between them an ICE table is needed. A K of 10^6 corresponds to a standard free energy change of about -34 kJ per mol at 298 K. Each 5.7 kJ per mol of delta G standard changes K by a factor of 10 at 298 K.
Common mistakes and connections: Students think a large K implies a fast reaction, or that K near 1 means equal amounts of species, which depends on stoichiometry. Another error is comparing K values of reactions that have different stoichiometry, such as different numbers of products, since the units and dependence on concentration differ. Direct link to delta G standard and to the kinetic versus thermodynamic distinction.
Visualization of Magnitude of K
K ranges over many orders of magnitude: values far above 1 mean near completion, values far below 1 mean almost no reaction, regardless of speed. The interactive lesson shows this as a live animation or chart.
Worked example and use case
The solubility product of AgCl is 1.8 x 10^-10, so very little silver chloride dissolves in water.
Frequently asked questions about Magnitude of K
What is Magnitude of K?
Large K favours products, small K favours reactants.
Is Magnitude of K a beginner, intermediate or advanced topic?
Magnitude of K is a intermediate topic in Kinetics & Equilibrium. It builds on the vocabulary of beginner topics in this area.
What should I learn before Magnitude of K?
Study these earlier topics in Kinetics & Equilibrium first: Equilibrium Constant, Kc and Kp, Reaction Quotient.
What comes after Magnitude of K?
The next topics in Kinetics & Equilibrium are Homogeneous and Heterogeneous Equilibria and Manipulating K.
Can I practise Magnitude of K with quizzes?
Yes. The interactive lesson includes a self-check question on Magnitude of K, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Where Magnitude of K fits in Kinetics & Equilibrium
Magnitude of K is topic 48 of 91 in Kinetics & Equilibrium.