CHEMICAL EQUILIBRIUM CHEMISTRY NOTES CHAPTER 09
Chemistry shams notes class 10 Chapter 09
Q.1: What is irreversible and reversible
reactions?
Ans: Irreversible
reactions:
"Those
chemical reactions which proceed in forwarding direction only are
called irreversible reactions." OR
"Those chemical reactions in which reactants are changed into products
only and products are not changed to reactants are called irreversible
reactions."
Characteristics of irreversible reactions:
Irreversible reactions have the following
characteristics:
i.
These reactions
proceed in one direction only.
ii.
They are represented by
a single arrow sign (------► )
iii.
No equilibrium state
is established in irreversible reactions.
iv. These reactions go to completion.
Reversible reactions:
"Those
chemical reactions which proceed both in forward and backwards
directions are called reversible reactions." OR
"Those chemical reactions in which the reactants react to form the
products and the products react to form the reactants back are called reversible
reactions."
Characteristics of reversible reactions:
A reversible reaction has the following characteristics:
- These reactions proceed in two directions i.e. forward and backwards
- These reactions never go to completion i.e. the reactants are not fully converted into products
The
detail about this general reversible reaction is given below;
i. Concentrations at the start:
At the start of the reaction, the concentrations of A and B are maximum
while that of C and D are zero.
ii. Concentrations after some time:
With the passage of time, the concentrations of C and D gradually increase while that of A and B gradually decreases.
iii.Variation of the rate of forward and reverse
reactions:
Change in concentrations of reactants or products per
unit time is called
rate of reaction.
In the beginning, the rate of forwarding the reaction is maximum while the rate of the reverse reaction is almost zero but as the time passes and sufficient amounts of C and Dare formed then the rate of backward
reaction increases
while that of forwarding reaction decreases until the rate of forwarding reaction becomes equal to the rate of the reverse reaction. Thus a state of. dynamic equilibrium is established.
iv.
Concentration at equilibrium state:
The concentrations of reactants or products
remain constant at equilibrium state. These
concentrations are called equilibrium concentrations.
v.
Graphical representation:
: FIGURE: Graph showing Reversible reaction and equilibrium state
Examples:
i. Change of a liquid to gas in a closed container:
Consider a closed container which is
partially filled with a liquid at a given temperature. At the start, evaporation starts and
the vapour molecules
are collected at the liquid surface. At the passage of time, the collected gas molecules over the liquid
surface convert to liquid back(condensation
starts). In the beginning rate of evaporation is faster than the rate of condensation but with the
passage of time the rate of
