DP Chemistry
Name: ____________________________
7 • Equilibrium
Guided Notes
7.1 Dynamic Equilibrium
Vocabulary: condensation, system, evaporation,
volatile, surroundings.
1. _________________. Liquid  gas
2. __________________ Gas  liquid
3. A ________________ liquid evaporates easily.
4. __________________
The
reactants
and
products involved in the chemical reaction being studied.
5. __________________ Everything in the universe except for the system.
7.1.1 Outline the characteristics of chemical and physical systems in a state of equilibrium.
6. Bromine is a volatile liquid at room temperature. Imagine we pour some bromine into a bottle and
put the lid on, which is called a _______________ system.

In a closed system, chemicals involved in the reaction cannot escape to the
_________________.

Be careful, bromine is poisonous.

The liquid bromine begins _________________ immediately.

The gaseous bromine that forms then condenses: slowly at first, then more ____________ as
the pressure of bromine increases.

Eventually, the rate of condensation = ________________ of evaporation, which means the
system has reached equilibrium.
7. Draw three pictures: 1. The beginning when there is no bromine gas, 2. After one minute, 3. After
equilibrium is reached.
1
2
3
8. The amount of liquid and gaseous bromine remain _____________________.
9. These pictures are of the molecular level, but on the macroscopic level, would you see any changes
in properties when the system is at equilibrium? _____.
10. The chemical equation of this reaction is drawn with a double arrow
⇄.
Write it:
11. The  reaction is called the ___________________ reaction.
12. The  reaction is called the ________________________________ reaction. If I tell a joke and you
don’t laugh at first that’s called a _____________________ reaction.
13. If you put some Br2(g) in a bottle, some liquid would form and increase until the system reached
_________________. The system can reach equilibrium by starting with only ________________
or only products, so we can say equilibrium can be reached from either direction.
14. Draw two graphs of this reaction: 3H2 + N2 ⇄ NH3.
Graph 2: starting with only products.
Concentration
Concentration
Graph 1: starting with reactants only.
Time
Time
15. Summarize the characteristics of equilibrium:
a.
Equilibrium is dynamic. The forward and back reactions occur at _________________ rate.
b.
Equilibrium is reached in a ________________ system because reactants and products can
react with each other.
c.
At equilibrium, the concentrations of reactants and products remain _____________ because
they are being produced and destroyed at the same rate.
d.
At equilibrium, there are no changes in macroscopic properties because the properties depend
only on the ___________________ of substances in the mixture.
e.
Equilibrium can be reached from ______________ direction.
7.2.1 Deduce the equilibrium constant expression (Kc) from the equation for a
homogeneous reaction.
16. Kc is called the _____________ ________________.
17. Kc has a ______________ value for a reaction at a chosen temperature. _________________ is
the only thing that can change Kc.
18. For the reaction 2A + B ⇄ 3C + D
Kc =
19. Deduce the equilibrium constant for this reaction: H2(g) + Br2(g) ⇄ 2HBr(g)
*I don’t think it will be on an IB exam, but liquids and solids do not go into the equilibrium expression.
Example: AgCl(s) ⇄ Ag+(aq) + Cl-(aq) Kc = [Ag+][Cl-]
7.2.2 Deduce the extent of a reaction from the magnitude of the equilibrium
constant.
20. K > 1 ______________ favored.
K = products/reactants
21. K < 1 ________________ favored.
22. When Kc is huge, the reaction goes almost to completion. (103 or higher)
23. When Kc is very small, the reaction hardly proceeds. (10-3 or smaller)
24. Example: For this reaction: H2(g) + Br2(g) ⇄ 2HBr(g), Kc = 108 at 550 K. Deduce the extent of the
completion. The reaction __________________________________________________
7.2.3 Apply Le Chatelier’s principle to predict the qualitative effects of changes
of temperature, pressure and concentration on the position of equilibrium and
on the value of the equilibrium constant. *Students will not be required to state Le
Chatelier’s principle.
25. Sakura and Sauske sometimes get chocolate bars from their parents. They have agreed to share
them equally between them, according to these two rules:
Rule #1: Whenever Sakura gets some chocolate, she gives half of it to Sasuke.
Rule #2: Sometimes, if they don’t do their chemistry homework, their parents might take away
some of the chocolate. . But they are caring IB learners, so the person that didn’t lose
chocolate will give half the amount lost to the other.
In these examples: state how many bars they will have after the change (apply their sharing rules). They
each start with 15 bars.
26. Sakura loses 10 bars. Sakura: __________ Sasuke: ___________
27. Sasuke receives 6 bars. Sakura: __________ Sasuke: ___________
28. Sakura receives 22 bars. Sakura: __________ Sasuke: ___________
29. This is an example of Le Chatelier’s Principle: a system at equilibrium when subjected to a change
will respond in such a way as to ___________________ the effect of the change.

Equilibrium shifts away from where you add (concentration, heat)

Shifts toward what you remove.
Effect of Concentration
30. If the forward reaction happens, we chemists say the equilibrium position “shifts right.”
For the reaction: A + B ⇄ C.
Change
Effect on equilibrium position
Increase [A]
Shifts right
Decrease [A]
Shifts left
Increase [C]
Decrease [C]
31. For this reaction: 3H2 + N2 ⇄ NH3
State what will happen for the following changes in concentration:
Change
Effect:
Increase [H2]
Shifts
Decrease [N2]
Shifts
Increase [NH3]
Shifts
32. What happens if
total pressure changes?
Let’s think. For this reaction:
CO(g) + 2H2(g) ⇄ CH3OH(g)
a.
The total moles gas on the left = _____
b.
Total moles gas on right = ______
c.
If total pressure increases, the system will try to _________________ the total pressure, and it
can do that by decreasing moles of gas, so the equilibrium position will shift __________.
d.
If total pressure decreases, the equilibrium position will shift ______________.
33. This reaction:
2HI(g) ⇄ H2(g) + I2(g)
Has ____ moles gas on the right and ____ moles gas on the left. What do you think will happen to
the equilibrium position if the pressure is increased? _________________________________
34. Remember, increasing pressure on a reaction with gasses ______________ the reaction rate. It is a
common misunderstanding that increasing reaction rate causes more products to form, but in
equilibrium reactions, if only reaction rate increases…
a.
Forward and __________________ reaction rates will increase, so
b.
Equilibrium will be reached more ___________________, but
c.
Equilibrium position will not _________________
Effect of Temperature
35. For exothermic reactions, think of heat as a product. If you increase temperature, it’s like you are
adding a ________________, so the position will shift ____________.
36. For endothermic reactions, think of heat as a __________________________.
temperature is like adding a _______________ and the position will shift ____________.
Increasing
7.2.4 State and explain the effect of a
catalyst
on an equilibrium reaction.
37. State and explain the effect of adding a catalyst
on:
a.
Reaction
rate:
________________
because catalysts provide a path with
____________ activation energy.
b.
Equilibrium position and Kc: ________________________ because the activation energy for
forward and reverse reactions has decreased, so they happen at ______________ rate.
7.2.5 Apply the concepts of kinetics and equilibrium to industrial
processes.
Suitable examples include the Haber and Contact processes.
38. The haber process is the following reaction:
N2(g) + 3H2(g)  2NH3(g) △H = -93 kJ mol-1
NH3 is a useful chemical for making fertilizers and many, many products. You and your group members
are part of the research and development team at a chemical company and must make as much
ammonia as possible, as fast as possible. Describe and explain what you recommend we do with the
following conditions (specific numbers not needed—just say high or low or moderate).
Conditions
Your recommendations +
explanation
Adding/removing
products
Total pressure
reactants
or
Actually used in the industry
Temperature
Use a catalyst (yes/no)
39. The contact process:
2SO2(g) +
O2(g)  2 SO3(g)
H = -197 kJ mol-1
Your company also wants you to research the contact process, which is used to
make fertilizers, paints and many other things. Explain and describe conditions
you recommend:
Conditions
Your recommendations +
explanation
Total pressure
Temperature
Use a catalyst (yes/no)
Actually used in the industry