Ch 16 – Chemical Equilibrium
Section 16.1 – The Concept of Equilibrium
What does it mean if a reaction is a reversible process?
The
products of a rxn can react to form reactants
What does it mean when a reaction has achieved equilibrium?
The concentrations of both
species reach levels where they remain constant
be the 2 processes are occurring at the same rate
The end of this section describes two important things to remember about equilibrium.
1. Equilibrium is a dynamic state. What does that mean?
both forward + reverse rxns continue to occur , although there is no net
change time
in reactant & product concentrations over
only reactants
2. Equilibrium can be established starting with _______________________________,
only products
with ______________________________, any mixture of reactants products
or with ____________________________.
+
Section 16.2 – The Equilibrium Constant
What information does a reaction quotient (Qc) tell you? The relative amounts of
products + reactants present at any given time in a rxn
What does the subscript “c” mean?
concentration
Write the reaction quotient expression for the balanced reaction aA + bB ⇌ cC + dD:
a
[C] [D]
Qc =
[A]"[B]3
Work through Worked Example 16.1. Once you understand the steps needed to solve this type
of problem, challenge yourself with the 3 Practice Problems (Attempt, Build, Conceptualize).
Write the rxn quotients for the following rxns-
a) N2(g) +
3Hn(g)2INH3(9)mQuw 2]
b) 20s(9) 30219 -
ot
1
, (QE)
equilibrium Constant (Kc)
For a system at equilibrium, the reaction quotient is equal to ___________________________.
Write the equilibrium constant expression (the law of mass action) for aA + bB ⇌ cC + dD:
D
notice it is the same as
Kc =
the reaction quotient equation
Work through Worked Example 16.2. Once you understand the steps needed to solve this type
of problem, challenge yourself with the 3 Practice Problems (Attempt, Build, Conceptualize).
Look at Table 16.1 on page 730. What do you notice about the value of Kc ([NO2]2/[N2O4]; last
column) when the experiment starts with different initial concentrations of NO2 and N2O4?
One of the things the equilibrium constant tells us is the extent to which ___________________
a reaction will
____________________________________________________________________________.
proceed at a particular temperature if we combine stoichiometric amounts of reactants
products
right or “favor _________.”
A reaction with a very large Kc value is often said to “lie to the _______”
left
A reaction with a very small Kc value is often said to “lie to the _______” reactants
or “favor _________.”
In general, what values of Kc are considered “large?” greater than 1x102
In general, what values of Kc are considered “small?” less than 1x10-2
values between 1x102 and 1x10 indicates neither products or reactants are strongly favored
Saying that a reaction “lies to the right” means it is ( spontaneous / nonspontaneous ) as written.
-
Saying that a reaction “lies to the left” means it is ( spontaneous / nonspontaneous ) as written.
-
2
Section 16.1 – The Concept of Equilibrium
What does it mean if a reaction is a reversible process?
The
products of a rxn can react to form reactants
What does it mean when a reaction has achieved equilibrium?
The concentrations of both
species reach levels where they remain constant
be the 2 processes are occurring at the same rate
The end of this section describes two important things to remember about equilibrium.
1. Equilibrium is a dynamic state. What does that mean?
both forward + reverse rxns continue to occur , although there is no net
change time
in reactant & product concentrations over
only reactants
2. Equilibrium can be established starting with _______________________________,
only products
with ______________________________, any mixture of reactants products
or with ____________________________.
+
Section 16.2 – The Equilibrium Constant
What information does a reaction quotient (Qc) tell you? The relative amounts of
products + reactants present at any given time in a rxn
What does the subscript “c” mean?
concentration
Write the reaction quotient expression for the balanced reaction aA + bB ⇌ cC + dD:
a
[C] [D]
Qc =
[A]"[B]3
Work through Worked Example 16.1. Once you understand the steps needed to solve this type
of problem, challenge yourself with the 3 Practice Problems (Attempt, Build, Conceptualize).
Write the rxn quotients for the following rxns-
a) N2(g) +
3Hn(g)2INH3(9)mQuw 2]
b) 20s(9) 30219 -
ot
1
, (QE)
equilibrium Constant (Kc)
For a system at equilibrium, the reaction quotient is equal to ___________________________.
Write the equilibrium constant expression (the law of mass action) for aA + bB ⇌ cC + dD:
D
notice it is the same as
Kc =
the reaction quotient equation
Work through Worked Example 16.2. Once you understand the steps needed to solve this type
of problem, challenge yourself with the 3 Practice Problems (Attempt, Build, Conceptualize).
Look at Table 16.1 on page 730. What do you notice about the value of Kc ([NO2]2/[N2O4]; last
column) when the experiment starts with different initial concentrations of NO2 and N2O4?
One of the things the equilibrium constant tells us is the extent to which ___________________
a reaction will
____________________________________________________________________________.
proceed at a particular temperature if we combine stoichiometric amounts of reactants
products
right or “favor _________.”
A reaction with a very large Kc value is often said to “lie to the _______”
left
A reaction with a very small Kc value is often said to “lie to the _______” reactants
or “favor _________.”
In general, what values of Kc are considered “large?” greater than 1x102
In general, what values of Kc are considered “small?” less than 1x10-2
values between 1x102 and 1x10 indicates neither products or reactants are strongly favored
Saying that a reaction “lies to the right” means it is ( spontaneous / nonspontaneous ) as written.
-
Saying that a reaction “lies to the left” means it is ( spontaneous / nonspontaneous ) as written.
-
2
