Definition of equilibrium: At equilibrium, the rate of the forward reaction is equal to the rate of the backward reaction.
Physical System
An example is bromine (placed in a sealed container at room temperature) Since this liquid is volatile, with a boiling point closer to the room temperature.
Diagram shows a layer of bromine gas formed above the liquid bromine. This occurs in both forms as bromine's boiling point is closer to room temperature, some particles have more kinetic energy in order to be in a gas form (evaporation), however when these gas particles collide with the surface of the liquid they lose energy and turn back into liquid (condensation). Therefore Equilibrium is only reached when rate of evaporation is equal to the rate of condensation
Chemical System
Whereas in hydrogen iodide, there are the elements Hydrogen and Iodine. Iodine (released as a purple gas) and hydrogen and hydrogen iodide (colourless gas). Equilibrium has been reached since the rate of reverse reaction is between the Iodine and Hydrogen gas. This is considered an equilibrium mixture
Heating Copper Sulfate (CuSO4) crystals
By heating the blue crystals, the hydrated CuSO4 crystals are converted to anhydrous CuSO4 crystals(turning from blue to white). This is a reversible reaction.
The hydrated (blue) Copper Sulfate crystals
Heating the blue Copper Sulfate
The anhydrous (white) Copper Sulfate
7.1.1 Great post Nathalie - I particularly like the copper burning to form a green flame - not so sure the last photos shows the anhydrous white copper sulfate though!
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