Outline the characteristics of a system in a state of equilibrium.
Many chemical reactions are reversible and never go to completion. Equilibrium can be approached from both directions. For a system in equilibrium the rate of the forward reaction equals the rate of the reverse reaction and the concentrations of all reactants and products remain constant. The system is closed and macroscopic properties remain constant. Use phase equilibrium as an example of dynamic equilibrium involving physical changes. In all reactions, there are in fact two reactions occurring, one where the reactants produce the products, and the other where the products react to form the reactants. In some reactions, this second reaction is insignificant, but in others there comes to a point where the two reactions exactly cancel each other out. Thus the reactants and products remain in equal proportions, though both are continually being used up and produced at the same time. For more IB description, see italics above.
2. State the equilibrium constant [removed]Kc) for a homogeneous reaction.
Consider equilibria involving one phase, gases or species in aqueous solution. The equilibrium constant is specific to a given system and varies with temperature. No calculations are required.
The equilibrium constant, Kc, is a constant which represents how far the reaction will proceed at a given temperature. This is specific to a given system, and this will vary with temperature. .
3. Deduce the extent of a reaction from the magnitude of the equilibrium constant.
When Kc >>1, the reaction goes almost to completion.
When Kc << 1, the reaction hardly proceeds.
When Kc is less then one, the reaction does not go to completion and reactants exceed products. When it is much less then one, the reaction hardly occurs at all (Kc can never be negative though, just close to 0). When Kc is greater then one, the reaction almost goes to completion, and when it is much greater then 1, the reactants left are insignificant.
