Transcript 18.2 Factors Affecting Chemical Equilibrium

1. Why does increased temperature increase the
reaction rate?
There will be more collisions.
It increases the average kinetic energy
More molecules have enough energy to
overcome the activation energy
2. How does a catalyst increase the rate of
reaction?
Lowers the activation energy and produce
products at a faster rate
Concentration and Temperature
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If a stress is applied to a system at
equilibrium, the system shifts in the direction
that relieves the stress.
Stresses include:
◦ Change in concentration
◦ Change in volume/pressure
◦ Change in temperature
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PCl5(g) ⇆ PCl3(g) + Cl2(g) ΔH=-47kJ
LE CHATELIER’S PRINCIPLE: WHEN A STRESS IS PLACED ON A REACTION
IN EQUILIBRIUM, THE REACTION WILL SHIFT IN SUCH A WAY TO RELEASE THE STRESS.
STRESS
↑ concentration
THE REACTION WILL….. As a result…
Shift away from the side of
the increase
↓ concentration
↑ temperature
↓ temperature
↑ pressure = ↓ volume
(gases only)
↓ pressure = ↑ volume
(gases only)
Shift towards the side of
the decrease
Shift away from the side of
the increase
Things on the same side of the
stress will do the opposite
thing as the stress.
Things on the opposite side of
the stress will do the same
thing as the stress.
Shift towards the side of
the decrease
Shift to the “fewer” (side
with less molecules of gas) The shift will point to what
side increases in
Shift to the “more” (side
concentration.
with more molecules of
gas)
The opposite side will
**LOOK AT
decrease in concentration.
COEFFICIENTS!!**
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Volume and pressure are related. As the volume
goes up the pressure goes down and vice versa.
(Boyles Law; P1V1=P2V2)
Only gases are affected by a change in
volume/pressure
You need to count the number of moles of gas
on each side of the reaction
If you add a catalyst, it does not make the reaction
favor one direction more than another. All it does is
makes the reaction rate increase, which makes the
reaction go to equilibrium faster.
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2H2O (g) ⇆ 2 H2(g) + O2(g)
The left side has 2 moles of gas, while the right
side has 3 moles of gas
If the stress is pressure increasing, shift toward
the side with the least number of moles of gas.
If the stress is pressure decreasing, shift toward
the side with the most number of moles of gas.
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Le Chatelier and Pressure - YouTube
PCl5(g) ⇆ PCl3(g) + Cl2(g)
**If you add a catalyst, it does not make the reaction favor one
direction more than another. All it does is makes the reaction rate
increase, which is making the reaction go to equilibrium faster.