chemistry Le chaterlier's principle

2. WHAT FACTORS STRESS YOU OUT?

3. HOW DO YOU C0PE WITH THESE
STRESSES?
 DIVERSIONS
… Rest
… Gather your self
… Pray

4. In today’s lesson, we will learn about Le
Chatelier’s Principle, which explain what a
system does at equilibrium in response to
“stresses”.

5. Once equilibrium is established, the reaction is over,
right? Not exactly.
Chemical equilibria can be shifted by changing the conditions that the
system experiences. We say that we “stress” the equilibrium. When we
stress the equilibrium, the chemical reaction is no longer at equilibrium,
and the reaction starts to move back toward equilibrium in such a way as
to decrease the stress. The formal statement is called Le Chatelier’s
principle: If an equilibrium is stressed, then the reaction shifts to reduce the
stress.

6. ACTIVITY
ACTION SHIFT IN EQUILIBRIUM
Adding more reactants Favors the forward reaction
Adding more products Favors the reverse reaction
Removing a reactant Favors the reverse reaction
Removing a product Favors the forward reaction
There are several ways to stress an equilibrium. Fill in the
table with the needed Information that would relate to Le
Chatelier’s Priciple.

8. ACTIVITY
ACTION SHIFT IN EQUILIBRIUM
Adding more reactants Favors the forward reaction
Adding more products Favors the reverse reaction
Removing a reactant Favors the reverse reaction
Removing a product Favors the forward reaction
There are several ways to stress an equilibrium. Fill in the
table with the needed Information that would relate to Le
Chatelier’s Priciple.

9. Le Chatelier’s Principle
Le Chatelier’s Principle states that “when stress is introduced
into a system of equilibrium, the system will adjust to relieve
the stress and regain equilibrium”. The stress is relieved as
the reaction shifts either to the left (reverse) or to the right
(forward) of the reversible action.

11. How does the activity relate to chemical reaction?
What do you think stresses a chemical reaction?
A chemical system can also be subjected to
stress and that there are ways to relieve those
stresses.

12. Stresses in a chemical system

13. Only applicable in gases…

14. At this time we will discuss about the hypothetical reaction at equilibrium:
Hypothetical Reaction
Equilibrium will shift to the side of the reaction
with fewer moles..

15. In this example, an increase in
pressure will cause equilibrium to
shift to the right, since there were
fewer moles – compared to 3 moles
to the left.
While in this example, a decrease in pressure means
that there is an increase in volume, so there is more
space. Euquiilibrium shifts to the side with more
moles, so in this example, equilibrium shfits to the left.

16. In Le Chatelier’s Priniciple, when a system at
equilibrium is stressed, the system works to restore
equilibrium

17. How a system at equilibrium responds to changes in temperature?
Le Chatelier’s Principle states that a chemical system at equilibrium always
works to restore equilibrium when it is stressed.
To consider what happens to a system at equilibrium when temperature is changed,
You must first consider the energetics of the reaction in question.
If the forward reaction is exothermic, then the reverse reaction must be
endothermic.
Chemical reactions that release energy are called exothermic.
Endothermic reactions are chemical reactions in which the reactants absorb heat energy
from the surroundings to form products

18. HYPOTHETICAL REACTION
CHANGE IN HEAT
This means that when forward
reaction occurs 75kJ of energy is
released.
75kL is absorbed when the
reverse reaction occurs

19. So an increase in temperature would
mean that the endothermic reaction
would be favoured to remove the
excess heat, therefore counter acting
the imposed stress.
Decreasing the temperature of the system would
cause the system to produce more energy;
therefore the exothermic would be favour. An
increase in temperature favours the endothermic
reaction.

20. Given this reaction at equilibrium:
N2 + 3H2 ⇄ 2NH3
In which direction—toward reactants or toward products—does the reaction shift
if the equilibrium is stressed by each change?
1. H2 is added. If H2 is added, there is now more reactant, so the reaction will shift toward
products to reduce the added H2.
3. NH3 is removed
2. NH3 is added. If NH3 is added, there is now more product, so the reaction will shift toward reactants to
reduce the added NH3.
, there is now less product, so the reaction will shift toward products to replace the
product removed.

21. Interpret the graph in terms of the effect of
varying pressure and temperature
conditions to the yield of ammonia.
From the plot, it can be
concluded that the yield of
ammonia can be maximized
with increasing pressure and
decreasing temperature. Both
conditions shift the equilibrium
towards the direction of
producing more ammonia.

22. ASSESSMENT:
Complete the following statements:
a) If additional reactant is added, the equilibrium shifts to reduce this stress
b) If additional product is added, the equilibrium. shifts to reactants to reduce the stress.
c) If reactant or product is removed, the equilibrium shifts to make more reactant or product,
respectively, to make up for the loss.
d.) A pressure increase shifts an equilibrium to the side of the reaction with the fewer number of moles
of gas,
e.) A pressure decrease shifts an equilibrium to the side of the reaction with the greater number of
moles of gas
Given this equilibrium, predict the direction of shift for each stress.
H2(g) + I2(s) + 53 kJ ⇄ 2HI(g)
a. decreased temperature toward reactants
b. increased pressure toward reactants
c. removal of HI toward products

23. Thank you……