Topic 7: Equilibrium F23
Fast Facts
Book Reading
Equilibrium MC
Equilibrium MC Answer
Practice Problems Equilibrium
Definition of Equilibrium and characteristics of
equilibrium condition.
Graphical relationship of equilibrium, conc vs. time and
rate vs. time.
Equilibrium is a special state or
condition for chemical reactions where
the rate of the forward reaction is equal
to the rate of the reverse reaction in a
Closed system.
Reactants < -- > Products
What happens when the equilibrium
condition is disturbed?
Equilibrium
Topic 7
How do you represent the equilibrium
condition and what does the value
mean?
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Dynamic Equilibrium
Equilibrium is a special state or condition
for chemical and physical processes.
Reactants < -- > Products
Equilibrium Condition
●
A process is to be at equilibrium
when the rate of the forward
reaction equals to the rate of the
reverse reaction.
Ratef = Rater
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Equilibrium Condition
●
If the Ratefoward = Ratereverse You can determine if your are at equilibrium, if
there is no net change in concentrations of the reactant and product.
Equilibriums systems are
dynamic.
Reactions go until they reach equilibrium,
they are always trying to get there
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Learning Check: Do you know the characteristics of
the equilibrium state?
Reactants are changing to
products and products to reactants,
reactions do really stop
Is one that is closed to
external factors.
On graphs that means the reach
a plateau they are unchanged.
Color is not changing, mass
is not disappearing
Reactants are changing to
products and products to
reactants,
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Equilibrium Constant expressions
●
●
Represent the equilibrium condition by
writing equilibrium constant expression Kc
Depends on the stoichiometry of rxn
aA
+
bB
< --- > cC
+ dD
K = [A]a[B]b
[C]c[D]d
●
●
Remember do not include pure liquids, solids in constant expressions.
The brackets Molarity = moles solute/ dm3 of solution
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The Magnitude of the Equilibrium constant
● The equilibrium constant is temperature dependent
● The magnitude of the equilibrium constant tells us the extent of
the reaction.
K >> 1 product favored RXN
K << 1 reactant favored RXN
Remember
K = [P]
[R]
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Book definition: When a change is applied to an equilibrium
mixture, the composition will react to minimize the effect of the
change. The new equilibrium mixtures will have different
concentration of reactant and product, but the value of Kc will
be unchanged, at the same temperature.
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Reactants < -- > Products
Product side,
K no change
Increase pressure shift to side with the
least number of gas molecules.
Reactant side,
K no change Decrease pressure shift to side with the
least number of gas molecules.
Reactant side,
K no change
Product side,
K no change
depends...exo (heat product)
Endo (heat reactant)/ K will change
No effect, just get to equilibrium faster
No effect, pure solids and liquids don’t change
equilibrium
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Equilibrium constant importance
● The magnitude of the equilibrium constant tells us the extent of the reaction.
K >> 1 product favored RXN
K << 1 reactant favored RXN
Remember
K = [P]
[R]
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Manipulation of K
Like Hess’s Law: The rules
If you flip an equation - take the reciprocal (inverse of the K) K = 1/K
If you multiply equation by factor - raise the concentration to that exponent.
When you add equations, you multiply all the Ks i.e. K1 x K2...
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Extent of the reaction (Q)
Suppose you do not know whether or not you are at equilibrium and you have
concentration values. You want to know for your concentrations which way the
reaction must go in order to achieve equilibrium.
Q < K reaction proceeds to the products
Q> K reaction proceeds to the reactants
Q = 1 equilibrium
Remember
Q = [P]
[R]
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Contact and Haber Process
Haber process - look the application of LeChatelier’s Principle to industrial
processes
N2 + 3H2 < -- > 2NH3 ΔH -92kJ/mol
What how can changes in concentration, temperature, addition of catalysts, and
pressure increase the yield of ammonia?
Which methods are dangerous, which methods are costly, ?
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Contact Process
The contact process is the process they use to make sulfuric acid.
2SO2 + O2 < -- > 2SO3
ΔH = -198kJ
What conditions can increase the yield
Pressure
Temperature
Catalysts
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Equilibrium HL: The equilibrium law
Calculating the equilibrium constant
The equilibrium constant tells us whether the reaction is reactant or product
favored.
To calculate the equilibrium constant
● Write equation
● Write equilibrium constant expression
● Determine the equilibrium concentration using ice box
● Plug into K expression
● Calculate K
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Practice Problems
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Free Energy and Equilibrium
Gibbs Free Energy:
●
●
Remember it told us the amount of free energy available to do work.
It also told us whether a reaction will occur spontaneously or not
○
○
○
ΔGo = - spontaneous
ΔGo = + nonspontaneous
ΔGo = 0 equilibrium
There are many ways to calculate ΔGo
● ΔGo = ΔH - TΔS (Takes into account entropy and enthalpy)
● ΔGo = ΔGfoproducts - ΔGforeactants (takes into account ΔGo is a state
function)
● ΔGo = -RT lnK (Relates ΔGo to equilibrium K)
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Free Energy and Equilibrium
ΔGo = -RT lnK (Relates ΔGo to equilibrium K)
K < 1 = nonspontaneous
K > 1 = spontaneous
K =1 = equilibrium
R = 8.314 J/K.mol
●
Complete CW Gibbs free energy
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