1. Le Chatelier’s Principle
equilibrium
balance
forward reaction
reverse reaction
changes in experimental conditions
disturb balance
equilibrium shifts
counteract disturbance
concentration
pressure
(gas phase)
temperature

2. Concentration
Fe3+ (aq)
+ SCN- (aq)
FeSCN2+ 
add Fe(NO3)3
add reactant Q
< K
add NaSCN
add reactant
add C2O42-
remove Fe2+ Q
> K
at equilibrium
change
K =
[FeSCN2+]
Q =
[FeSCN2+]
[Fe3+]
[SCN-]
[Fe3+]
[SCN-]
ratef = kf
[Fe3+]
[SCN-]

3. Pressure
N2O4 (g)  2
NO2 (g)
at 25oC, K = 10.38
increase P
by adding reactant or product
K =
[NO2]eq2
add N2O4
Q =
[NO2]eq2
[N2O4]eq
[N2O4]i Q
< K

4. Pressure
N2O4 (g)  2
NO2 (g)
decrease volume
[N2O4]
= mol N2O4
increase [N2O4] V
[NO2]
= mol NO2
increase [NO2] V
(6.0)2
= 11.9
K =
[NO2]2
= (3.0)2
Q =
= 10.3
(1.74)
[N2O4]
(0.87) Q
> K
decrease volume
decrease n
increase n
increase volume
Δn = 0
no effect of pressure

5. Pressure N2O4 (g)  2 NO2 (g) add inert gas 1.00 M Ar [NO2] = 3.0 M
= 3.0 mol/L
increase P
[N2O4]
= 0.87 M
= 0.87 mol/L
PV = nRT
at 298 K
P(1.0 L)=
(4.87)
(.08206)
(298) P
(1.0 L)
= (3.87)
(.08206)
(298)
P = 119 atm
P = 95 atm 2
PNO
=(3/3.87)
(95)
=73 atm 2
PNO =
(3/4.87)
(119)
=73atm 2 4
PN O
= (.87/3.87)
(95)
=22atm KP
unchanged
Kp =
(73)2
/ 22
= 242

6. Temperature
changes K
heat
heat +
N2O4 (g)  2
NO2 (g)
+heat
ΔH = 58.0 kJ
treat heat
reactant
product
endothermic
exothermic
ΔH > 0
ΔH < 0
raising T
adding heat as reactant
ΔH > 0
lowering T
removing heat as product
ΔH < 0

7. Calculations
reaction table
ICE table
H2 (g)
+ I2 (g)
 2HI (g)
at 453oC,
calculate K
at equilibrium,
[H2] = M
= 0.50
– x
x = 0.393
K =
[HI]2eq
= (2x)2 =
(0.786)2 =
54.3
[H2]eq
[I2]eq
(0.50–x)
(0.50–x)
(0.107)2
[H2] (M)
[I2] (M)
[HI] (M)
Initial
0.50
0.50
0.00
Change
- x
- x
+2x
0.50 – x 2x
Equilibrium
0.50 – x

8. Calculations
K =
54.3
H2 (g)
+ I2 (g)
 2HI (g)
K =
54.3 =
( x)2
x = .782
Q =
(.224)2
= .195
< K
x = .355
(.623 – x)
(.414 – x)
(.623)
(.414)
x =
-b ±
50.3x2
- 57.2x
= 0 
b2 – 4ac 2a
ax2 bx c
[H2] (M)
[I2] (M)
[HI] (M)
Initial
.623
.414
.224
Change
- x -x
+2x
Equilibrium x x x