What are key take-aways that I need to know to meet the info below. Enduring understandings are the long-term takeaways related
to the big ideas that leave a lasting impression on students. Learning objectives define what a student needs to be able
to do with content knowledge in order to progress toward the
enduring understandings.
Essential knowledge statements describe the knowledge
required to perform the learning objective. 
Content:
ENDURING UNDERSTANDING
TRA-6
Some reactions can occur in both forward and reverse directions, sometimes
proceeding in each direction simultaneously.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
TRA-6.A
Explain the relationship
between the occurrence
of a reversible chemical or
physical process, and the
establishment of equilibrium,
to experimental observations.
TRA-6.A.1
Many observable processes are reversible.
Examples include evaporation and
condensation of water, absorption and
desorption of a gas, or dissolution and
precipitation of a salt. Some important
reversible chemical processes include the
transfer of protons in acid-base reactions and
the transfer of electrons in redox reactions.
TRA-6.A.2
When equilibrium is reached, no observable
changes occur in the system. Reactants and
products are simultaneously present, and
the concentrations or partial pressures of all
species remain constant.
TRA-6.A.3
The equilibrium state is dynamic. The
forward and reverse processes continue
to occur at equal rates, resulting in no net
observable change.
TRA-6.A.4
Graphs of concentration, partial pressure, or
rate of reaction versus time for simple chemical
reactions can be used to understand the
establishment of chemical equilibrium.
ENDURING UNDERSTANDING
TRA-6
Some reactions can occur in both forward and reverse directions, sometimes
proceeding in each direction simultaneously.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
TRA-6.B
Explain the relationship
between the direction in
which a reversible reaction
proceeds and the relative
rates of the forward and
reverse reactions.
TRA-6.B.1
If the rate of the forward reaction is greater
than the reverse reaction, then there is a net
conversion of reactants to products. If the
rate of the reverse reaction is greater than
that of the forward reaction, then there is a
net conversion of products to reactants. An
equilibrium state is reached when these rates
are equal.
ENDURING UNDERSTANDING
TRA-7
A system at equilibrium depends on the relationships between concentrations,
partial pressures of chemical species, and equilibrium constant K.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
TRA-7.A
Represent the reaction
quotient Qc p
 or Q , for a
reversible reaction, and the
corresponding equilibrium
expressions Kc = Qc
 or
K
p = Qp
.
TRA-7.A.1
The reaction quotient Q
c c
 describes the relative
oncentrations of reaction species at any time.
For gas phase reactions, the reaction quotient
may instead be written in terms of pressures
as Qp
. The reaction quotient tends toward the
equilibrium constant such that at equilibrium
Kc = Qc
 and K
p = Qp
. As examples, for the
reaction
aA + bB  cC + dD
the equilibrium expression for (Kc
, Qc
) is
EQN: [ ] [ ]
[ ] [ ]
K = C D
A B c
c d
a b
and that for (K
p
, Qp
) is
EQN: K = (P ) (P )
(P ) (P ) p
c d
a b
C D
A B
X CONVERSION BETWEEN Kc AND Kp WILL
NOT BE ASSESSED ON THE AP EXAM.
Rationale: Conversion between K and K is an c p
algorithm that does not deepen understanding of
equilibrium. However, students should be aware
of the conceptual differences and pay attention to
whether Kc or Kp is used in an exam question.
X EQUILIBRIUM CALCULATIONS ON
Rationale: The need to account for the relative
volumes of the liquid and gas phase is complex in
these mixed equilibria.
TRA-7.A.2
The reaction quotient does not include
substances whose concentrations (or partial
pressures) are independent of the amount,
such as for solids and pure liquids.
ENDURING UNDERSTANDING
TRA-7
A system at equilibrium depends on the relationships between concentrations,
partial pressures of chemical species, and equilibrium constant K.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
TRA-7.B
Calculate Kc
 or K
p
based on
experimental observations of
concentrations or pressures
at equilibrium.
TRA-7.B.1
Equilibrium constants can be determined
from experimental measurements of the
concentrations or partial pressures of the
reactants and products at equilibrium.
ENDURING UNDERSTANDING
TRA-7
A system at equilibrium depends on the relationships between concentrations,
partial pressures of chemical species, and equilibrium constant K.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
TRA-7.C
Explain the relationship
between very large or very
small values of K and the
relative concentrations
of chemical species
at equilibrium.
TRA-7.C.1
Some equilibrium reactions have very large K
values and proceed essentially to completion.
Others have very small K values and barely
proceed at all. 
ENDURING UNDERSTANDING
TRA-7
A system at equilibrium depends on the relationships between concentrations,
partial pressures of chemical species, and equilibrium constant K.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
TRA-7.D
Represent a multistep
process with an overall
equilibrium expression,
using the constituent
K expressions for each
individual reaction.
TRA-7.D.1
When a reaction is reversed, K is inverted.
TRA-7.D.2
When the stoichiometric coefficients of a
reaction are multiplied by a factor c, K is raised
to the power c.
TRA-7.D.3
When reactions are added together, the K of
the resulting overall reaction is the product of
the K’s for the reactions that were summed.
TRA-7.D.4
Since the expressions for K and Q have
identical mathematical forms, all valid algebraic
manipulations of K also apply to Q.
ENDURING UNDERSTANDING
TRA-7
A system at equilibrium depends on the relationships between concentrations,
partial pressures of chemical species, and equilibrium constant K.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
TRA-7.E
Identify the concentrations or
partial pressures of chemical
species at equilibrium based
on the initial conditions and
the equilibrium constant.
TRA-7.E.1
The concentrations or partial pressures of
species at equilibrium can be predicted given
the balanced reaction, initial concentrations,
and the appropriate K.
ENDURING UNDERSTANDING
TRA-7
A system at equilibrium depends on the relationships between concentrations,
partial pressures of chemical species, and equilibrium constant K.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
TRA-7.F
Represent a system
undergoing a reversible
reaction with a
particulate model.
TRA-7.F.1
Particulate representations can be used to
describe the relative numbers of reactant
and product particles present prior to
and at equilibrium, and the value of the
equilibrium constant. 
ENDURING UNDERSTANDING
TRA-8
Systems at equilibrium respond to external stresses to offset the effect of
the stress.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
TRA-8.A
Identify the response of a
system at equilibrium to an
external stress, using Le
Châtelier's principle.
TRA-8.A.1
Le Châtelier’s principle can be used to predict
the response of a system to stresses such
as addition or removal of a chemical species,
change in temperature, change in volume/
pressure of a gas-phase system, or dilution of a
reaction system.
TRA-8.A.2
Le Châtelier’s principle can be used to
predict the effect that a stress will have on
experimentally measurable properties such as
pH, temperature, and color of a solution.
ENDURING UNDERSTANDING
TRA-8
Systems at equilibrium respond to external stresses to offset the effect of
the stress.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
TRA-8.B
Explain the relationships
between Q, K, and the
direction in which a reversible
reaction will proceed to
reach equilibrium.
TRA-8.B.1
A disturbance to a system at equilibrium
causes Q to differ from K, thereby taking
the system out of equilibrium. The system
responds by bringing Q back into agreement
with K, thereby establishing a new
equilibrium state.
TRA-8.B.2
Some stresses, such as changes in
concentration, cause a change in Q only.
A change in temperature causes a change in K.
In either case, the concentrations or partial
pressures of species redistribute to bring Q
and K back into equality
ENDURING UNDERSTANDING
SPQ-5
The dissolution of a salt is a reversible process that can be influenced by
environmental factors such as pH or other dissolved ions.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
SPQ-5.A
Calculate the solubility of a
salt based on the value of K
sp
for the salt.
SPQ-5.A.1
The dissolution of a salt is a reversible process
whose extent can be described by K
sp, the
solubility-product constant.
SPQ-5.A.2
The solubility of a substance can be calculated
from the K
sp for the dissolution process. This
relationship can also be used to predict the
relative solubility of different substances.
SPQ-5.A.3
The solubility rules (see TRA-2.A.5) can be
quantitatively related to K
sp, in which K
sp
values >1 correspond to soluble salts.
ENDURING UNDERSTANDING
SPQ-5
The dissolution of a salt is a reversible process that can be influenced by
environmental factors such as pH or other dissolved ions.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
SPQ-5.B
Identify the solubility of
a salt, and/or the value
of K
sp for the salt, based
on the concentration of a
common ion already present
in solution.
SPQ-5.B.1
The solubility of a salt is reduced when it is
dissolved into a solution that already contains
one of the ions present in the salt. The impact
of this “common-ion effect” on solubility can be
understood qualitatively using Le Châtelier’s
principle or calculated from the K
sp
for the
dissolution process.
ENDURING UNDERSTANDING
SPQ-5
The dissolution of a salt is a reversible process that can be influenced by
environmental factors such as pH or other dissolved ions.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
SPQ-5.C
Identify the qualitative effect
of changes in pH on the
solubility of a salt.
SPQ-5.C.1
The solubility of a salt is pH sensitive when one
of the constituent ions is a weak acid or base.
These effects can be understood qualitatively
using Le Châtelier’s principle.
X COMPUTATIONS OF SOLUBILITY AS A function of pH
ENDURING UNDERSTANDING
SPQ-5
The dissolution of a salt is a reversible process that can be influenced by
environmental factors such as pH or other dissolved ions.
LEARNING OBJECTIVE ESSENTIAL KNOWLEDGE
SPQ-5.D
Explain the relationship
between the solubility
of a salt and changes
in the enthalpy and
entropy that occur in the
dissolution process.
SPQ-5.D.1
The free energy change (ΔG°) for dissolution
of a substance reflects a number of factors:
the breaking of the intermolecular interactions
that hold the solid together, the reorganization
of the solvent around the dissolved species,
and the interaction of the dissolved species
with the solvent. It is possible to estimate the
sign and relative magnitude of the enthalpic
and entropic contributions to each of these
factors. However, making predictions for the
total change in free energy of dissolution can
be challenging due to the cancellations among
the free energies associated with the three
factors cited.