Download Chemistry Name: LeChâtlier`s Principle Date: Chemical Equilibrium

Chemistry
Name:________________________
LeChâtlier’s Principle
Date:__________________
Chemical Equilibrium and LeChâtelier’s Principle
Dynamic Equilibrium: A forward reaction and reverse reaction will happen at the same rate,
reaching equilibrium and no net change
LeChâtlier’s Principle: When a stress is applied to a system in equilibrium, the reaction will
shift to relieve the stress.
What is meant by stress? For example:
The concentration of a gas is increased, shift away
The concentration of a gas is decreased, shift toward
Total pressure is increased (or volume decreased),toward side with less moles of gas
Total pressure is decreased (or volume increased),toward side with more moles of gas
Increase the temperature, shift away from heat
Decrease the temperature, shift toward heat
Endothermic = heat is a reactant (+∆H)
Exothermic = heat is a product (-∆H)
There are cases where the equilibrium is not shifted:

If the amount of a solid or liquid is added or removed, the equilibrium will not shift.

If a catalyst is added to speed up the reaction, the equilibrium will not shift.

Add an inert (unreactive) gas no effect on equilibrium. (He, Ne, Ar, Kr, Xe, Rn)
1.
For the reaction below, which change would cause the equilibrium to shift to the right?
CH4 (g) + 2H2S(g) ↔ CS2(g) + 4H2(g)
a.
Decrease the concentration of dihydrogen sulfide.
b. Increase the pressure on the system.
c.
Increase the temperature of the system.
d. Increase the concentration of carbon disulfide.
e.
Decrease the concentration of methane.
2. What would happen to the position of equilibrium when the following changes are made to
the equilibrium system below?
2SO3(g) ↔ 2SO2(g) + O2(g)
a.
Sulfur dioxide is added to the system. left
b. Sulfur trioxide is removed from the system. left
c.
Oxygen is added to the system. left
3. What would happen to the position of equilibrium when the following changes are made to
the reaction below?
2HgO(s) ↔ Hg(l) + O2(g)
a.
HgO is added to the system. no effect
b. The pressure on the system increases. left
4. When the volume of the following mixture of gases is increases, what will be the effect of
the equilibrium position? Why? Left, pressure decreases, favor the side with more moles
4HCl(g) + O2(g) ↔ 2H2O(g) + 2Cl2(g)
5. Predict the effect of decreasing the volume of the container for each equilibrium.
a.
2H2O(g) + N2(g) ↔ 2H2(g) + 2NO(g) left
b. SiO2(s)
c.
+ 4HF(g) ↔ SiF4(g) + 2H2O(g) right
CO(g) + H2(g) ↔ C(s) + H2O(g) right
6. Predict the effect of decreasing the temperature on the position of the following equilibria.
* A negative enthalpy (∆H) value indicates an exothermic reaction and a positive value
indicates an endothermic reaction.
a.
H2(g) + Cl2(g) ↔ 2HCl(g) + 49.7 kJ
b. 2NH3(g)
c.
↔ N2(g) + 3H2(g)
CO(g) + H2(g) ↔ C(s) + H2O(g)
right
∆H = 37.2 kJ
left
∆H = -27.6 kJ
right