Download Lesson 4624-4627 Effect on Equilibrium copy

4.6 The rate and extent of chemical change
4.6.2 Reversible reactions and dynamic equilibrium
4.6.2.4 The effect of changing conditions on
equilibrium
The relative amounts of all the reactants and
products at equilibrium depend on the conditions of
the reaction.
If a system is at equilibrium and a change is made to
any of the conditions, then the system responds to
counteract the change.
The effects of changing conditions on a system at
equilibrium can be predicted using Le Chatelier’s
Principle.
Specification
Describe Le Chatelier’s principle.
Explain the effects on equilibrium of changing conditions using suitable examples.
Research the work of Le Chatelier or the life of Fritz Haber. Highlight the moral ambiguity
of Haber’s work.
Scientific Communication Skills
4.6 The rate and extent of chemical change
4.6.2 Reversible reactions and dynamic equilibrium
Use data to predict the effect of concentration on equilibrium. Justify answers.
4.6.2.5 The effect of changing concentration
If the concentration of one of the reactants or
products is changed, the system is no longer at
equilibrium and the concentrations of all the
substances will change until equilibrium is reached
again.
If the concentration of a reactant is increased, more
products will be formed until equilibrium is reached
again.
If the concentration of a product is decreased, more
reactants will react until equilibrium is reached
again.
Specification
Scientific Communication Skills
4.6 The rate and extent of chemical change
4.6.2 Reversible reactions and dynamic equilibrium
Use data to predict the effect of temperature on equilibrium. Justify answers.
4.6.2.6 The effect of temperature changes on
equilibrium
If the temperature of a system at equilibrium is
increased:
•the relative amount of products at equilibrium
increases for an endothermic reaction,
•the relative amount of products at equilibrium
decreases for an exothermic reaction.
If the temperature of a system at equilibrium is
decreased:
•the relative amount of products at equilibrium
decreases for an endothermic reaction,
•the relative amount of products at equilibrium
increases for an exothermic reaction.
Specification
Scientific Communication Skills
4.6 The rate and extent of chemical change
4.6.2 Reversible reactions and dynamic equilibrium
Use data to predict the effect of pressure on equilibrium. Justify answers.
4.6.2.7 The effect of pressure changes on
equilibrium
For gaseous reactions at equilibrium:
•an increase in pressure causes the equilibrium
position to shift towards the side with the smaller
number of molecules as shown by the symbol
equation for that reaction,
•a decrease in pressure causes the equilibrium
position to shift towards the side with the larger
number of molecules as shown by the symbol
equation for that reaction.
Specification
Scientific Communication Skills
The effect of changing conditions on equilibrium
Friday, 10 June 2022
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An aqueous solution of blue copper(II) ions can react with aqueous chloride ions to
form a yellow copper compound. The ionic equation for this reaction is:
Cu2+ + 4Cl- ⇋ [CuCl4]21.
2.
3.
4.
5.
The forward reaction is endothermic. What two things can you say about the
enthalpy change for the reverse reaction?
A solution containing copper(II) ions is mixed with a solution containing chloride
ions in a flask. The solution quickly turns green. When observed for a few
minutes no further change in colour can be seen. Explain these observations.
Suggest two changes that could be made to the mixture that would change its
colour.
Why would a change in pressure not change the colour of the solution?
Would the addition of a colourless catalyst change the colour of the solution?
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Keywords
Counteract
Le Chatelier’s Principle
Qualitative
System
Gaseous
Equilibrium shift
Test
The effect of changing conditions on equilibrium
Friday, 10 June 2022
Learning Objectives - To be able to:
Keywords
• Make qualitative predictions about the effect of changes on systems at
equilibrium when given appropriate information.
• Interpret appropriate given data to predict the effect of a change in concentration
of a reactant or product on given reactions at equilibrium.
• Interpret appropriate given data to predict the effect of a change in temperature
on given reactions at equilibrium.
• Interpret appropriate given data to predict the effect of pressure changes on
given reactions at equilibrium.
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Intro
Develop
Practice
Counteract
Le Chatelier’s Principle
Qualitative
System
Gaseous
Equilibrium shift
Test
4.6.2.3 Equilibrium
Explain the term equilibrium and give suitable examples of when it can occur
When a reversible reaction occurs in apparatus which prevents the escape of reactants and products – a closed
system – equilibrium is reached when the forward and reverse reactions occur at exactly the same rate:
At the start of the
reaction, there are only
reactants, the forward
reaction is fast
There is now a lower
concentration of
reactants – the forward
reaction slows down
At the start of the
reaction, there are no
products, the reverse
reaction cannot start yet
The forward reaction has
now slowed down to the
same rate as the reverse
reaction
The reverse reaction has
now sped up to the same
rate as the forward
reaction
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There is now a higher
concentration of
products – the reverse
reaction speeds up
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Test
4.6.2.3 Equilibrium
Explain the term equilibrium and give suitable examples of when it can occur
When a reversible reaction occurs in apparatus which prevents the
escape of reactants and products – a closed system – equilibrium is
reached when the forward and reverse reactions occur at exactly the
same rate.
Once the forward and reverse reactions are going at the same rate,
there is no longer any net change in the concentration of reactants
and products – this is dynamic equilibrium (Note: this is not
necessarily at 50% reactants 50% products).
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4.6.2.3 Equilibrium
Explain the term equilibrium and give suitable examples of when it can occur
• This equilibrium has more products than reactants – we say it lies to the right.
• This equilibrium has more reactants than products – we say it lies to the left.
• If a system is at equilibrium and a change is made to any of the conditions, then
the system responds to counteract the change.
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4.6.2.4 The effect of changing conditions on equilibrium
Make qualitative predictions about the effect of changes on systems at equilibrium
• At equilibrium, both forward and backward reactions are still happening, but
there is no overall effect – it is a dynamic equilibrium. This means that the
concentrations of the reactants and products have reached a balance and do
not change.
• If a system is at equilibrium and a change is made to any of the conditions,
then the system responds to counteract the change.
• The effects of changing conditions on a system at equilibrium can be
predicted using Le Chatelier’s Principle.
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Test
4.6.2.5 The effect of changing concentration
Predict the effect of a change in concentration of a reactant or product on given reactions at equilibrium
• If you change the concentration of either the reactants or products, the
system will no longer be at equilibrium.
• So the system responds to bring itself back to equilibrium again.
• If you increase the concentration of the reactants the system tries to
decrease it by making more products.
• If you decrease the concentration of the products the system tries to
increase it again by reducing the amount of reactants.
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4.6.2.5 The effect of changing concentration
Predict the effect of a change in concentration of a reactant or product on given reactions at equilibrium
Easy to remember:
• Increase the concentration, shift is to other
side of arrow.
• Decrease the concentration, stay on same side
of arrow.
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4.6.2.5 The effect of changing concentration
Predict the effect of a change in concentration of a reactant or product on given reactions at equilibrium
• Increasing the concentration of a chemical will make equilibrium shift in the
direction that will use it up
Increase
ammonium chloride
NH4Cl (s)
ammonia
NH3 (g)
+
hydrogen chloride
HCl (g)
Equilibrium shifts left
Increase
Hydrated copper sulfate
CuSO4.5H2O (s)
anhydrous copper sulfate
CuSO4 (s)
+
water
5H2O (l)
Equilibrium shifts right
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Test
4.6.2.5 The effect of changing concentration
Predict the effect of a change in concentration of a reactant or product on given reactions at equilibrium
• Decreasing the concentration of a chemical will make equilibrium shift in the
direction that will replace it
Decrease
ammonium chloride
NH4Cl (s)
ammonia
NH3 (g)
+
hydrogen chloride
HCl (g)
Equilibrium shifts right
Decrease
Hydrated copper sulfate
CuSO4.5H2O (s)
anhydrous copper sulfate
CuSO4 (s)
+
water
5H2O (l)
Equilibrium shifts left
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Test
4.6.2.6 The effect of temperature changes on equilibrium
Predict the effect of a change in temperature on given reactions at equilibrium
• All reactions are exothermic in one direction and endothermic in the other.
• If you decrease the temperature, the equilibrium will move in the
exothermic direction to produce more heat. This means you’ll get more
products for the exothermic reaction and fewer products for the
endothermic reaction.
• If you raise the temperature, the equilibrium will move in the endothermic
direction to try to decrease it. You’ll get more products for the endothermic
reaction and less products for the exothermic reaction.
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Test
4.6.2.6 The effect of temperature changes on equilibrium
Predict the effect of a change in temperature on given reactions at equilibrium
Easy to remember:
• Increase the temperature, shift is in the
endothermic direction.
• Decrease the temperature, shift is in the
exothermic direction.
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Test
4.6.2.6 The effect of temperature changes on equilibrium
Predict the effect of a change in temperature on given reactions at equilibrium
• Increasing the temperature favours the endothermic reaction (takes in heat):
endothermic
ammonium chloride
ammonia
exothermic
NH4Cl (s)
NH3 (g)
+
hydrogen chloride
HCl (g)
Equilibrium shifts right
endothermic
Hydrated copper sulfate
anhydrous copper sulfate
exothermic
CuSO4.5H2O (s)
CuSO4 (s)
+
nitrogen
N2 (g)
water
5H2O (l)
Equilibrium shifts right
exothermic
hydrogen
3H2 (g)
+
ammonia
2NH3 (g)
endothermic
Equilibrium shifts left
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Test
4.6.2.6 The effect of temperature changes on equilibrium
Predict the effect of a change in temperature on given reactions at equilibrium
• Decreasing the temperature favours the exothermic reaction (takes in heat):
endothermic
ammonium chloride
ammonia
exothermic
NH4Cl (s)
NH3 (g)
+
hydrogen chloride
HCl (g)
Equilibrium shifts left
endothermic
Hydrated copper sulfate
anhydrous copper sulfate
exothermic
CuSO4.5H2O (s)
CuSO4 (s)
+
nitrogen
N2 (g)
water
5H2O (l)
Equilibrium shifts left
exothermic
hydrogen
3H2 (g)
+
ammonia
2NH3 (g)
endothermic
Equilibrium shifts right
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Test
4.6.2.7 The effect of pressure changes on equilibrium
Predict the effect of pressure changes on given reactions at equilibrium
• Changing the pressure only affects equilibria involving gases.
• If you increase the pressure, the equilibrium tries to reduce it – it moves in
the direction where there are fewer molecules of gas.
• If you decrease the pressure, the equilibrium tries to increase it – it moves in
the direction where there are more molecules of gas.
• You must use the balanced symbol equation for a reaction to see which side
has more molecules of gas.
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Test
4.6.2.7 The effect of pressure changes on equilibrium
Predict the effect of pressure changes on given reactions at equilibrium
Easy to remember:
• Increase the pressure, shift is to fewer
molecules.
• Decrease the pressure, shift is to more
molecules.
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Test
4.6.2.7 The effect of pressure changes on equilibrium
Predict the effect of pressure changes on given reactions at equilibrium
• Increasing the pressure favours the side with the fewest gas moles:
ammonium chloride
NH4Cl (s)
ammonia
NH3 (g)
+
hydrogen chloride
HCl (g)
Equilibrium shifts left
hydrogen
3H2 (g)
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+
nitrogen
N2 (g)
I Do
ammonia
2NH3 (g)
We Do
Equilibrium shifts right
You Do
Test
4.6.2.7 The effect of pressure changes on equilibrium
Predict the effect of pressure changes on given reactions at equilibrium
• Decreasing the pressure favours the side with the most gas moles:
ammonium chloride
NH4Cl (s)
ammonia
NH3 (g)
+
hydrogen chloride
HCl (g)
Equilibrium shifts right
NB: if you have the same number of molecules of gas on each
side, a change in pressure will have no effect on the position
of the equlibrium
hydrogen
3H2 (g)
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+
nitrogen
N2 (g)
I Do
ammonia
2NH3 (g)
We Do
Equilibrium shifts left
You Do
Test
Answer the following questions in full sentences in your exercise books.
1. What is Le Chatelier’s Principle?
2. What three factors can be changed in a system at equilibrium?
3. If the concentration of a reactant is increased what will happen to the products of the
reaction?
4. What will happen to the amount of product in an exothermic reaction at equilibrium if the
temperature is increased?
5. What will happen to the amount of product in an endothermic reaction at equilibrium if
the temperature is decreased?
6. What would happen to the position of equilibrium in a gaseous reaction if the pressure is
increased?
7. What will happen if we increase the temperature of the reaction below? Explain why you
think this.
exothermic
N2(g) + 3H2(g)
2NH3(g)
8. Explain what will happen if we decrease the pressure in the reaction above.
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