Chemical Equilibrium Flashcards
When has a system reached equilibrium?
When the forward and reverse rates are equal.
What is the equilibrium constant?
[C]^c * [D]^d
K = ——————–
[A]^a * [B]^b
Why does it look like nothing is happening at equilibrium?
The concentrations are not changing, but the reactions are still taking place in equal rate.
What does a large K mean?
Equilibrium doesn’t occur until the concentration of reactants is small.
What does a small K mean?
Equilibrium occurs almost immediately and relatively little product is produced.
What is Le Châtlier’s Principle
If a stress is placed on a system in equilibrium, the equilibrium is displaced in the direction that counteracts the effects of the stress.
If the reactant concentration is increased, what happens to the equilibrium?
It is shifted to the right. Decrease to the left.
If the product concentration is increased, what happens to the equilibrium?
It is shifted to the left. Decrease to the right.
If temperature increases, what happens to the equilibrium?
it is shifted in the direction that absorbs heat (the change is because temperature changes Keq)
If pressure increases, what happens to the equilibrium?
It shifts in the direction that decreases the number of molecules.
In heterogeneous reactions, what is special about the Keq?
It does not include [Solids]
Why is Ka only for weak acids?
Strong acids dissociate completely and therefore are not in equilibrium.
What does the size of Ka mean?
Smaller Ka = weaker acid.
What is the formula for Ka?
[A+]^a * [B-]^b
Ka = ——————–
[AB]
What do we know because 0.1M or lower weak acids dissociate very little?
[AB at equilibrium] ≈ [AB originally]
