’
Which is an empirical formula?
(1) P
2
O
5
(2) P
4
O
6
(3) C
2
H
4
(4) C
3
H
6

’
Which is an empirical formula?
(1) P
2
O
5
(2) P
4
O
6
(3) C
2
H
4
(4) C
3
H
6

AIM:
How does a reaction at equilibrium change when it is disturbed?
DO NOW :
What is equal at equilibrium?

We can change the concentrations of reactants and products by disturbing or
“ stressing ” a reaction

When disturbed the reaction will make adjustments to restore equilibrium
The new equilibrium position is different, which means the amounts of reactants and products are changed
The change in equilibrium is called a “ shift ” in the equilibrium position

The chemist Henri Le
Chatelier studied equilibrium conditions
He developed rules for changing equilibrium based on his experiments

’
Any stress applied to a reaction in dynamic equilibrium causes the reaction to make a “ shift ” to relieve the stress
A shift towards product formation is a shift to the right
A shift towards reactant formation is a shift to the left
1)
2)
3)
Stresses to a reaction include:
Concentration changes
Pressure/volume changes
Temperature changes

Changes in the amount or concentration of a product OR reactant will disturb (stress) an reaction at equilibrium
The reaction adjusts to minimize any stresses h in reactants causes a shift toward products h in products causes a shift toward reactants i in reactants causes a shift toward reactants i in products causes a shift toward products

Given the reaction (see image) at equilibrium:
What occurs when the concentration of H
2
(g) is increased?
1. The rate of the forward reaction increases and the concentration of N
2
(g) decreases.
3. The rate of the forward reaction and the concentration of
N
2
(g) both increase.
2. The rate of the forward reaction decreases and the concentration of N
2
(g) increases.
4. The rate of the forward reaction and the concentration of
N
2
(g) both decrease

If the volume of a reaction changes the equilibrium is disturbed i in volume causes an h in pressure
The equilibrium will shift to relieve pressure if the pressure is h and h pressure if the pressure is i
Increasing and decreasing pressure is based on the # of moles of gas
To i pressure there is a shift toward the side of the reaction with the least # of moles of gas

Ammonia is produced commercially by the
Haber reaction: . . . (see image)
The formation of ammonia is favored by
1. an increase in pressure
3. removal of N
2
(g)
2. a decrease in pressure
4. removal of H
2
(g)

Changing temperature alters both the equilibrium position and the equilibrium constant
Reactions are either endothermic or exothermic
If a fwd rxn is exothermic the rev rxn will be endothermic
An h in temp causes a shift in the direction where heat is absorbed
(endothermic) i in temp causes a shift toward where heat is produced

What occurs when the temperature is increased in a system at equilibrium at constant pressure?
1. The rate of the forward reaction increases, and the rate of the reverse reaction decreases.
2. The rate of the endothermic reaction increases.
3. The rate of the forward reaction decreases, and the rate of the reverse reaction increases.
4. The rate of the exothermic reaction decreases.

Given the equilibrium reaction in a closed system as shown:
What will be the result of an increase in temperature?
1. The equilibrium will shift to the left and [H
2
] will increase.
3. The equilibrium will shift to the right and [HI] will increase.
2. The equilibrium will shift to the left and [H
2
] will decrease.
4. The equilibrium will shift to the right and [HI] will decrease.

Given the reaction at equilibrium: . . . (see image)
Which change will cause the equilibrium to shift?
1. increase in pressure
3. addition of heat
2. increase in volume
4. addition of a catalyst

Given the reaction at equilibrium (see image):
The concentration of A(g) can be increased by
1. lowering the temperature
3. increasing the concentration of AB (g)
2. adding a catalyst
4. increasing the concentration of B (g)

Given the reaction at equilibrium: . . . (see image)
Which change will shift the equilibrium to the right?
1. increasing the temperature
3. decreasing the amount of SO
2
(g)
2. increasing the pressure
4. decreasing the amount of O
2
(g)