This document discusses reversible reactions and how they relate to closed systems. It introduces the concept of reversible reactions which can proceed in both directions, using examples like the heating and cooling of copper sulfate. It then explains that a closed system at dynamic equilibrium occurs when the forward and backward reaction rates are equal. Finally, it describes how temperature and pressure can impact the equilibrium position - increasing temperature favors the endothermic direction, while increasing pressure favors the side with fewer moles of gas.

1. REVERSE REACTION

2. Reversible Reactions
OK, let’s introduce
you to a new
symbol and
concept.

3. Reversible Reactions

4. Reversible Reactions
This is the
symbol for
a reversible
reaction

5. Reversible Reactions
A reversible
reaction is one
which can go in both
directions.

6. Reversible Reactions
This means that in a
chemical reaction the
products of the reaction can
be turned back into the
original reactants.

7. Reversible Reactions
For example:
A + B C + D

8. Reversible Reactions
For example:
A + B C + D
A and B react to produce C and D, but
also C and D can react to produce A
and B.

9. Reversible Reactions
Let’s look at an
example

10. Reversible Reactions
Heating blue
copper sulphate
Heat
Water
vapour

11. Reversible Reactions
Heating blue
copper sulphate
Heat
Water
vapour
White
anhydrous
copper
sulphate

12. Reversible Reactions
Blue
hydrated
copper
sulphate
White
anhydrous
copper
sulphate
Add a few
drops of
water

13. Reversible Reactions
Blue
hydrated
copper
sulphate
White
anhydrous
copper
sulphate
Add a few
drops of
water
CuSO4.5H2O CuSO4 + 5H2O

14. Reversible Reactions
Let’s look at
another example –
favourite one in
the exams!

15. Reversible Reactions
Let’s look at
another example –
favourite one in
the exams!
The Thermal
Decomposition
of ammonium
chloride,
NH4Cl

16. Reversible Reactions
NH4Cl NH3 + HCl
Heat
Water in
and out
Solid ammonium
chloride
Solid ammonium
chloride
Ammonia and
HCl gases

17. Reversible Reactions
NH4Cl NH3 + HCl
Heat
Water in
and out
Solid ammonium
chloride
Solid ammonium
chloride
Ammonia and
HCl gases
1. When heated. Ammonium
chloride splits up into
ammonia gas and hydrogen
chloride gas.

18. Reversible Reactions
NH4Cl NH3 + HCl
Heat
Water in
and out
Solid ammonium
chloride
Solid ammonium
chloride
Ammonia and
HCl gases
1. When heated. Ammonium
chloride splits up into
ammonia gas and hydrogen
chloride gas.
2. As these gases cool on the
bottom of the flask, they
recombine to form solid
ammonium chloride again.

19. Reversible Reactions
NH4Cl NH3 + HCl
Heat
Water in
and out
Solid ammonium
chloride
Solid ammonium
chloride
Ammonia and
HCl gases
1. When heated. Ammonium
chloride splits up into
ammonia gas and hydrogen
chloride gas.
2. As these gases cool on the
bottom of the flask, they
recombine to form solid
ammonium chloride again.
3. This is a good example of
a reversible reaction
because the products
recombine to easily form
the original reactants.

20. Reversible Reactions and
Closed Systems

21. Reversible Reactions and
Closed Systems
Try to imagine a closed
system where no more
reactants are added, and
no products are removed.

22. Reversible Reactions and
Closed Systems

23. Reversible Reactions and
Closed Systems
A + B C + D
A and B will be combining to form C and D,
while at the same time C and D will be
combining to form A + B.

24. Reversible Reactions and
Closed Systems
A + B C + D
A point will eventually be reached when the
rate of the forward reaction is equal to the
rate of the backward reaction.

25. Reversible Reactions and
Closed Systems
A + B C + D
This point is know as the
DYNAMIC EQUILIBRIUM

26. Reversible Reactions and
Closed Systems
Temperature and equilibria
A + B C + D
If the forward reaction (i.e. going from left to right) is
ENDOTHERMIC and heat energy is taken in ……..

27. Reversible Reactions and
Closed Systems
Temperature and equilibria
A + B C + D
If the forward reaction (i.e. going from left to right) is
ENDOTHERMIC and heat energy is taken in ……..
Then if the
temperature is
increased.

28. Reversible Reactions and
Closed Systems
Temperature and equilibria
A + B C + D
If the forward reaction (i.e. going from left to right) is
ENDOTHERMIC and heat energy is taken in ……..
Then if the
temperature is
increased.
The yield of
products is
increased, and
more heat is
taken in.

29. Reversible Reactions and
Closed Systems
Temperature and equilibria
A + B C + D
If the forward reaction (i.e. going from left to right) is
ENDOTHERMIC and heat energy is taken in ……..
Then if the
temperature is
decreased

30. Reversible Reactions and
Closed Systems
Temperature and equilibria
A + B C + D
If the forward reaction (i.e. going from left to right) is
ENDOTHERMIC and heat energy is taken in ……..
Then if the
temperature is
decreased.
The yield of
products is
decreased, and
less heat is
taken in.

31. Reversible Reactions and
Closed Systems
Temperature and equilibria
A + B C + D
If the forward reaction (i.e. going from left to right) is
EXOTHERMIC and heat energy is given out……..

32. Reversible Reactions and
Closed Systems
Temperature and equilibria
A + B C + D
If the forward reaction (i.e. going from left to right) is
EXOTHERMIC and heat energy is given out……..
Then if the
temperature is
increased.

33. Reversible Reactions and
Closed Systems
Temperature and equilibria
A + B C + D
If the forward reaction (i.e. going from left to right) is
EXOTHERMIC and heat energy is given out……..
Then if the
temperature is
increased.
The yield of
products is
decreased, and
less heat is given
out.

34. Reversible Reactions and
Closed Systems
Temperature and equilibria
A + B C + D
If the forward reaction (i.e. going from left to right) is
EXOTHERMIC and heat energy is given out……..
Then if the
temperature is
decreased.

35. Reversible Reactions and
Closed Systems
Temperature and equilibria
A + B C + D
If the forward reaction (i.e. going from left to right) is
EXOTHERMIC and heat energy is given out……..
Then if the
temperature is
decreased.
The yield of
products is
increased, and
more heat is
given out.

37. Reversible Reactions and
Closed Systems
What about gases and
equilibria?

38. Reversible Reactions and
Closed Systems
Pressure and equilibria

39. Reversible Reactions and
Closed Systems
Pressure and equilibria

40. Reversible Reactions and
Closed Systems
Pressure and equilibria

41. Reversible Reactions and
Closed Systems
Pressure and equilibria Increasing the pressure will
push the reaction in the
direction of fewer molecules

42. Reversible Reactions and
Closed Systems
Pressure and equilibria Increasing the pressure will
push the reaction in the
direction of fewer molecules
Increased pressure

43. Reversible Reactions and
Closed Systems
Pressure and equilibria Increasing the pressure will
push the reaction in the
direction of fewer molecules
Decreased pressure

44. End of Section 4 Lesson 4
In this lesson we have covered:
Reversible reactions
Reversible reactions in closed systems