Chemistry · Reactivity 2: How much, how fast and how far?. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Many reactions are reversible. In a closed system they reach dynamic equilibrium: the forward and reverse reactions are still going on, at equal rates, so the concentrations stay constant. They are constant, not necessarily equal.
The equilibrium constant, Kc, puts product concentrations over reactant concentrations. A large K means mostly products; a very small K means mostly reactants. Only a change in temperature changes K.
Le Châtelier's principle: when a system at equilibrium is disturbed, the position shifts in the direction that reduces the change. Use it for changes in concentration, pressure and temperature. A catalyst speeds up both directions equally, so it does not move the position.
Students say K changes when concentration or pressure changes. The position of equilibrium shifts, but the value of K stays the same unless the temperature changes.
Answer: The mixture turns a darker brown and Kc increases.
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