Write down everything you can
think of about this reaction:
Nitrogen + Hydrogen
⇌
⇌ Ammonia
reaction is reversible
rate of forward reaction = rate of reverse reaction
exothermic in one direction endothermic in the other
energy absorbed in one direction is equal to energy
released in the other
elements making compound
N2(g) + 3H2(g) ⇌ 2NH3(g)
4.6 Chemical Equilibrium
Objective: to explain chemical equilibrium and how conditions
affect it, using the example of the Haber Process.
Outcomes:
All: I can define the term chemical equilibrium (D/E)
Most: I can explain the Haber Process (C)
Some: I can determine the affects of changing conditions on
reversible reactions (A/B)
Keywords: equilibrium, reversible,
closed system, conditions, yield,
catalyst
Homework: Haber Process
worksheet
Due: Thursday 2 May
What is equilibrium?
The below graphs show what happens to the reaction rate and
amounts of reactants and products in a closed system.
Equilibrium
A closed system
is where none
of the reactants
or products or
energy can get
out.
Use the graphs to
write a definition of
equilibrium.
I can define the term chemical equilibrium (D/E)
What is equilibrium?
Equilibrium
Equilibrium
The point in a
reversible reaction
where the forward
and reverse rates
of reaction are
equal. Therefore
the amounts of
reactants and
products remain
the same.
I can define the term chemical equilibrium (D/E)
The Haber Process
Nitrogen + Hydrogen
⇌ Ammonia
N2(g) + 3H2(g) ⇌ 2NH3(g)
Uses of
Ammonia
- fertilisers
I can explain the Haber Process (C)
The Haber Process
Nitrogen + Hydrogen
⇌ Ammonia
N2(g) + 3H2(g) ⇌ 2NH3(g)
What is the main use of ammonia?
Made into
ammonium nitrate
FERTILISER
Plants need nitrogen to
grow. They cannot absorb
it from the air. Nitrates in
the soil are absorbed
through the roots
I can explain the Haber Process (C)
Reversible Reactions and Conditions
The position of the equilibrium
will shift to cancel out
any change in conditions
This means the
reaction can be
shifted from one
direction to the the
other.
Conditions
CONCENTRATION
TEMPERATURE
PRESSURE
CATALYST
I can determine the affects of changing conditions on reversible
reactions (A/B)
Reversible Reactions and Conditions
A(aq) + 2B(aq) ⇌ C(aq) + 3D(l) ENDO
What happens to the equilibrium if the concentration
of B is increased?
It moves to the right to use up B and makes more
products.
If the concentration of C is increased the
equilibrium shifts to the _________
to the
LEFT
C and make makes more
use up ___
___________.
REACTANTS
CONCENTRATION
Reversible Reactions and Conditions
[Co(H2O)6]2+ + 4Cl- ⇌ CoCl4 + 6H2O ENDO
hexaaquacobalt(II) + hydrochloric acid ⇌ cobalt chloride + water
pink
blue
If the temperature is decreased for a
reaction which is endothermic in the
forward direction, the equilibrium shifts to
the ________
LEFT to ________
INCREASE the temperature
and make more REACTANTS
_________
TEMPERATURE
Reversible Reactions and Conditions
N2(g) + 3H2(g) ⇌ 2NH3(g) EXO
What are the optimum temperature conditions to
increase yield in the Haber Process?
LOW TEMPERATURES 450°C
If the temperature is ___________
DECREASED for a
reaction which is exothermic in the forward
direction, the equilibrium shifts to the
_________
RIGHT to ________
INCREASE the temperature
and make more _________.
PRODUCTS
TEMPERATURE
Reversible Reactions and Conditions
1 N2(g) + 33H2(g) ⇌ 2NH3(g) EXO
What are the optimum pressure conditions to
increase yield in the Haber Process?
How
many
molecules of GAS200atm
are on each side?
HIGH
PRESSURES
If the pressure is ___________
INCREASED the
equilibrium shifts to the _________
RIGHT to the
side with the least number of molecules and
makes more _________.
PRODUCTS
PRESSURE
Reversible Reactions and Conditions
Write down 4 key features of a catalyst.
A catalyst:
1. increases rate of reaction
2. is not used up in the reaction
3. lowers the activation energy
4. provides an alternate pathway for the reaction.
A catalyst does not affect the equilibrium as it has
an equal effect on the rate of the forward and
reverse reactions.
CATALYST
Reversible Reactions and Conditions
To help with yields and the compromise in
temperature and pressure in the Haber Process a
catalyst is added.
N2(g) + 3H2(g) ⇌ 2NH3(g) EXO
CATALYST
IRON
MEDIUM PRESSURES 200atm
MEDIUM TEMPERATURES 450°C
I can explain the Haber Process (C)
Q. Hydrogen for use in the Haber process can be produced by reacting
methane with steam. The methane and steam mixture is passed over a
nickel catalyst at 800°C and a pressure of 30 atmospheres. The
equation for this reaction is:
CH4(g) + H2O(g) CO(g) + 3H2(g)
The forward reaction is endothermic.
ai What conditions of temperature would increase the yield of products
for the forward reaction at equilibrium? Explain your answer. (2)
ii Suggest why a temperature of 800°C, not higher or lower, is used in
the industrial process.[H] (2)
bi What conditions of pressure would increase the yield of products
from the forward reaction at equilibrium? Explain your answer. (2)
ii Suggest one reason why a pressure of 30 atmospheres is used in the
industrial process. [H] (1)
Answers
ai High temperature; forward reaction is endothermic or forward
reaction takes in energy (allow heat). /2
ii Not higher because energy costs would be high(er) or apparatus
would be more expensive or apparatus would need to withstand
higher temperatures; not lower because rate of reaction would be
slow(er) or catalyst would not work. /2
bi Low pressure; forward reaction produces more molecules (of gas)
or more (gas) molecules on right side of equation. /2
ii Some pressure is needed to move gases through apparatus or to
increase the rate of reaction. /1
I can determine the affects of changing conditions on reversible
reactions (A/B)
4.6 Chemical Equilibrium
Objective: to explain chemical equilibrium and how conditions
affect it, using the example of the Haber Process.
Outcomes:
All: I can define the term chemical equilibrium (D/E)
Most: I can explain the Haber Process (C)
Some: I can determine the affects of changing conditions on
reversible reactions (A/B)
Keywords: equilibrium, reversible,
closed system, conditions, yield,
catalyst
Homework: Haber Process
worksheet
Due: Thursday 2 May