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Irreversible reactions
Most chemical reactions are considered irreversible ­
the products that are made cannot readily be changed
back into their reactants.
For example, when wood burns
it is impossible to turn it back
into unburnt wood again!
Similarly, when magnesium
reacts with hydrochloric acid to
form magnesium chloride and
hydrogen, it is not easy to
reverse the reaction and obtain
the magnesium.…read more

Slide 3

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What are reversible reactions?
Reversible reactions occur when the backwards reaction
(products reactants) takes place relatively easily under
certain conditions. The products turn back into the reactants.
A + B C + D
(reactants) (products)
For example, during a reversible reaction reactants A and B
react to make products C and D.
However, products C and D can also undergo the reverse
reaction, and react together to form reactants A and B.…read more

Slide 4

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Heating ammonium chloride
An ammonium salt can be made by reacting ammonia with
an acid. Some of the salt will decompose back into the
reactants when heated.
hydrogen ammonium
ammonia + chloride chloride
NH3 (g) + HCl (g) NH4Cl (s)
NH4Cl reforms in
NH4Cl decomposes the cooler part of
back into NH3 and the test tube
HCl gases when
heated…read more

Slide 5

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Reversible reactions and dynamic equilibrium
A reversible chemical reaction is a dynamic process.
For a reversible reaction,
reactants products
a state of dynamic equilibrium is said to be established when
rate of forward rxn = rate of backward rxn
Apparently, there is no change in the concentrations of
reactants and products.…read more

Slide 6

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Concept of Dynamic Equilibrium
If conditions on either side of the fence are equally pleasant, an equal
number of sheep will be on either side of the fence, despite the fact that
sheep are constantly jumping over the fence. If one side is preferable
(sunny rather than rainy), there will be more sheep on the nicer side.…read more

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