Concept of Equilbrium
• Equilibrium is achieved when opposing
processes proceed at equal rates.
A
B
In chemical equilibria, forward and reverse reactions
occur at equal rates.
Forward reaction
A! B
Rate=
Reverse reaction
B!A
Rate=
Equilibrium does not tell you about
the rate of the reaction.
N2(g) + O2(g)
2NO(g)
K ~10-30
Therefore,
2NO(g)
N2(g) + O2(g)
K ~1030
BUT, NO(g) is stable at room temp.
!
What DOES affect equilibrium?
1. concentration
2. volume (if gases are involved)
3. temperature (changes the value of Kc)
At equilibrium,
•Concentrations of reactants and products
do not change over time.
Dynamic balance
CATALYSTS affect the RATE of a reaction, but
not Keq.
•Reaching equilibrium may be slow!
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Catalysts do not effect equilibrium
concentrations.
A
B
Calculations of Kc
The value of the equilibrium constant Keq is NOT affected
by the presence of a catalyst.
At temperatures near 800 oC, steam passed
over hot coke (a form of carbon obtained
from coal), reacts to form CO and H2:
C(s) + H2O(g)
CO(g) + H2(g)
The mixture of gases that results is an
important industrial fuel called water gas.
When equilibrium is achieved at 800 oC;
[H2] = 4.0 x 10"2 M,
[CO] = 4.0 x 10"2 M
[H2O] = 1.0 x 10"2 M.
Calculate Kc at this temperature
! A catalyst lowers ________________________
between the reactants and products.
! Lowering the activation energy increases ____
______ of a reaction, both forward and backward.
! The catalyst increases the rate at which
equilibrium is achieved, but it does not change the
_________________ of the equilibrium mixture.
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a)
b)
c)
d)
0.16
1.6 #10"3
4.0
6.25
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Manipulations of Equilibrium
Constants
Manipulation of Equilibrium
Constants:
!Keq in the reverse direction is the
_______ of the forward reaction Keq.
What is the value of the equilibrium constant for
the following reaction?
N2(g) + O2(g) + Br2(g)
2NOBr(g)
Kc =??
Given the following data:
2NO(g) + Br2(g)
2NO(g)
2NOBr(g)
N2(g) + O2(g)
Kc =2.0
Kc = 2.1. #1030
!Keq of a reaction that has been
multiplied by an integer is the
original Keq ____________________.
!If the net reaction is made up of 2
or more steps, Keq is the
___________ of the individual Keq's
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Using the Equilibrium Constant
Using the Equilibrium Constant
2. Predict direction of a reaction
Q $ reaction quotient
Information obtained from Kc
1. Which are favored?
Reactants or products?
For the following reaction Keq is 3.9 ! 10
CaF2(s)
The equilibrium constant for the following reaction
at 150°C is 8.5#10"3.
11
2IBr(g)
Br2(g)+ I2(g)
+2
Ca (aq) + 2F (aq)
If there are 0.02 moles of I2, 0.05 moles of Br2 and
0.30 moles of IBr then:
In the equilibrium reaction mixture:
A products dominate
B reactants dominate
C There is a reasonable mixture of reactants and
products
D only products exist.
E. only reactants exist.
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a) the system is at equilibrium.
b) the system is not at equilibrium and the
products will react to produce more IBr(g) in
order to get to equilibrium. (The reaction will
proceed to the left.)
c) the system is not at equilibrium and the reactant
(IBr) will react to produce more Br2(g) and I2(g)
in order to get to equilibrium. (The reaction will
proceed to the right.)
d) the system can never get to equilibrium.
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Using the Equilibrium Constant
Le Chatelier’s Principle
3. Obtaining equilibrium concentrations
of reactants and products.
At 750ºC. Kp = 0.770 for the reaction below.
CO2(g) + H2(g)
CO(g) + H2O(g)
If 0.200 atm of CO2 and H2 are admitted to a rigid
container and allowed to reach equilibrium. What is
the equilibrium partial pressure of CO?
If a system at equilibrium is disturbed by
changing:
• Concentration of one of the components
• Temperature
• Pressure
the concentrations will shift to counteract the
disturbance.
Fe3+(aq) + SCN-(aq)
yellow colorless
heat + CaCO3 (s)
[Fe(SCN)]2+(aq)
red
CaO(s) + CO2(g)
heat + Co[H2O]6+2(aq) + 4Cl"(aq)
pink
CoCl4"2(aq)+ 6H2O(l)
blue
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