Reversible reaction
The chemical reactions in which
the products of the reactions can also react with one another under suitable
conditions to give back the original reactants are known as reversible
reactions.
In such reactions, a double half
headed arrow mark is put between the reactant and the product species. Some
example of reversible reactions:
PCL5(s)DPCL3(g)+CL2(g)
H2(g)+L2(g)D2HL(g)
Characteristics
I.
Reversible
reactions involving one or more gaseous species take place in a closed vessel.
II.
The
reversible reactions never proceed to completions.
III.
The
rate of reactions in a particular direction depends upon the molar conc. Of the
reacting species.
IV.
A
reversible reaction attains equilibrium under a given set of conditions.
V.
The
state of equilibrium can be changed by changing the conditions such as
temperature, pressure, volume etc.
VI.
Dynamic
nature- Equilibrium in reversible reactions is dynamics. It means that both
forward and the backward reactions continue to proceed even at the state of
equilibrium but the rate of the forward reaction is equal to the rate of the
backward reactions.
When a
reactions attains the state of equilibrium, all measurable properties such as
temperature, pressure, concentration, density, colour etc. Get fixed
Irreversible reactions
The
reaction in which the products formed but they do not react with each other to
produce original reactants is known as irreversible reactions.
Or
The reaction
which have only forward direction to form product but don’t has backward
reaction to return the original reactants
Ex:
I.
Acid
base reactions: HCL + NaCl žNaCl+H2O
II.
Combustion reactions: CH4 + 2O2žCO2
+ 2H2O
III.
Redox reactions: CuSO4 + Zn ž ZnSO4 + Cu.
Classifications of Equilibrium
We have
seen that dynamic equilibrium may be set up in a physical as well as chemical
process.
Physical process:
The state
of equilibrium attained in physical process such as evaporation, condensation,
fusion etc. Is called physical equilibrium.
Characteristics of physical equilibrium
I.
The
measurable properties of the system becomes constant because the concentrations
of the substance is in equilibrium become fixed.
II.
In
case a substance in equilibrium is in the gaseous or vapour from, the
equilibrium can be established only in closed vessel.
III.
When
equilibrium is attained, there an expression this acquires constant value at a
given temperature. Consider
the following equilibrium : H2O(l)DH2O(v)
At equilibrium,
pressure becomes constant.
IV.
The
magnitude of the constant value of concentration related expression indicates
the extent to which the reaction proceeds before the establishment of
equilibrium.
V.
The
equilibrium is dynamic in nature. It means that the process does not stop after
the establishment of equilibrium but here the rate of the forward reaction
becomes equal to the rate of the backward reactions.
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