00:01
We need to explain the definition of equilibrium as it applies to the context of chemical systems, and we also need to provide two different examples for dynamic equilibrium.
00:12
If we think about a chemical reaction of reactant a, reversibly producing product b, then we know that from kinetics, because this is a reversible reaction, we can form rate expressions for both the forward and reverse directions of this reaction.
00:28
The forward rate would be if we defined a rate constant for the forward rate to be k sub 1, and a rate constant for the reverse of this reaction to be k -sub -negative 1, and the forward rate would be equal to k -1 times a concentration of a, and the reverse rate would be k -sub -negative 1 times a concentration of b.
00:54
When we are at equilibrium, the key distinction for being at equilibrium, is that the forward and reverse rates are equal to one another.
01:11
And when this is the case, there is no net change in species concentrations with time.
01:23
And so because these two expressions are equal to one another, we can define an equilibrium constant in terms of equilibrium concentrations for both species to be k sub 1.
01:38
Over k sub negative 1, which is equal to the concentration of b over the concentration of a.
01:52
And now for two different examples for dynamic equilibrium, if we have water at its vapor pressure, then we know that there is liquid that is vaporizing into the gaseous phase, and there is also vapor that is condensing back down into the liquid phase...