Le Chatelier's principle.
DEFINITION: “When a system at equilibrium is subjected to a change in temperature, pressure, concentration, or volume, the system will adjust itself in such a way as to counteract the effect of that change and restore a new state of equilibrium.”
We will consider the influences of all of the above factors.
- Is it the forward or reverse reaction that counteracts the change?
- Does the new equilibrium lie further to the right or left —
increasing or decreasing the percentage yield? - How is reaction rate influenced by the change in factor.
- What are the most economic conditions to use?
ANALOGY: A boy running down an escalator that is moving up ⇒
He may appears to be standing still if his speed matches the escalator’s speed. Let’s consider what he’d do if the escalator was speeded up:
- initially he would begin to back-up because he’d be moving slower
- to counteract the change he would speed up
- he would need to start running faster than the escalator
if he wants to get back to the position he was in - in dynamic equilibrium terms, he won’t return all the way back, but he will get back to a new stable position near to where he was
- at this new dynamic equilibrium his movement will match the escalator’s movement again, but he won’t be quite as far down.
