Transcript Chapter 16 Chemical Equilibrium

Chapter 16
Chemical Equilibrium
Different States a System Can Be In
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A state of change
No change (there are several no change states
No Change States
static system – no movement, no change
(example: a rock in a jar)
steady state system – is a flow through
system with no net change, is an open system
(example: the earth and the flow of energy
from the sun to the earth and then into outer
space)
equilibrium – the forward process is equal to
the reverse process so there is no net change,
is a closed system
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Equilibrium examples
a reversible chemical reaction
2NO2(g) ↔ N2O4(g)
The forward and reverse reactions are taking
place at the same time.
When the rate of the forward reaction is equal
to the rate of the reverse reaction, the system is
at equilibrium.
The law of Chemical
Equilibrium
 Every reversible reaction proceeds to an
equilibrium state.
 Regardless of how much of each chemical
you start with the system will shift so that
concentrations of the products divided by the
concentrations of the reactants will always
be a constant.
 Do sample problem page 543
 Assign practice problems 1 & 2 on page 543
Equilibrium constant is Keq
If Keq  1 the products are favored.
Keq  1 the reactants are favored.
The concentrations of the pure solids or liquids
can be left out of the formula – Their
concentration does not change and becomes
part of the Keq.
Do sample problem 2 on page 545
Assign practice problems 3 & 4 on page 545
(write Keq and give the equation)
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Reaction Quotient
The reaction quotient is the same mathematical
expression as Keq only it is taken when the
system is not at equilibrium.
Le Chatelier’s Principle
(leh-shaht-lee-ay)
When pressure (stress) is placed on a system
the system will shift to relieve the pressure
(stress).
Increasing the pressure will favor the side that
requires less volume.
2NO2(g) ↔
N2O4(g)
Changing the pressure will change the
equilibrium constant.
Adding a compound to an
equilibrium
This will “push” the reaction to favor the
other side of the equation.
2NO2(g) ↔
N2O4(g)
This will remove some of the compound that
has been added.
This does not change the equilibrium constant.
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Removing a compound
2NO2(g) ↔
N2O4(g)
This will cause the equilibrium to shift to favor
(make more of) the material that is being
removed.
This does not change the equilibrium constant.
Effects of changing Temperature
H2 + I2 ↔ 2HI + heat
Adding heat will drive the reaction to the
left.
Removing heat (cooling) pulls the reaction to
the right.
This will change the equilibrium constant
Chapter questions page 558-559 (1 - 14, 17,
18, 20, 21, 23, 24, 26, 27, 28, 29)