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1. NAVODAYA VIDYALAYA SAMITI, NOIDA
E-CONTENT FOR CLASS XI-CHEMISTRYR
UNIT-07
EQUILIBRIUM
PREPARED BY:
M SIMHADRI APPANNA
PGT CHEMISTRY
JNV WEST GODAVARI(AP)

2. INTRODUCTION
• When one or more substances are combine to
form a new substance is called chemical reaction
• In a reaction two components are there, one is in
left hand side known as reactant and right side is
called product.
• If reactants are converted in products is termed as
forward reaction. in the same way products are
turned in to reactants is known as backward
reaction.

3. When a liquid evaporates in a closed
container, molecules relatively higher kinetic
energy escape the liquid surface in to the
vapour phase and number of the molecules
from the vapour strike the liquid surface and
are retained in the liquid phase. It give rise to
a constant vapour pressure because of
equilibrium in which the number of molecules
leaving the liquid equals the number returning
to liquid from the vapour. We say that the
system in equilibrium state

4. ▪ The mixture of the
reactants and products
is called equilibrium
mixture.
▪ The stage where there
is no change the
concentrations is called
equilibrium.
▪ Equilibrium involves
ions are called Ionic
equilibrium.

5. EQUILIBRIUM IN PHYSICAL
PROCESS
▪The most famous
examples of physical
equilibrium is the
phase transformation
process
▪That is given below:
▪Solid
▪Liquid
▪Solid
liquid
gas
gas

6. The concept of
equilibrium
As a system
approaches
equilibrium, both
the forward and
backward reactions
are occurring
At equilibrium , the
forward and
backward reactions
are proceeding at
the same rate

7. System of
Equilibrium
▪Once equilibrium
is achieved the
amount of each
reactant and
product remains
constant
▪Here NO2 and
N2O4 has reached
equilibrium.

9. The opposing forces involve only physical changes
the equilibrium is physical equilibrium
▪ solid- liquid equilibrium
solid liquid
H20(s) H2O(l)
•Liquid- Vapour equilibrium
Liquid
H2O(l)
Gas
H2O(g)
•Solid-vapour equilibrium
Camphor (solid) Camphor (vapour)
NH4Cl (solid) NH4Cl (vapour)

10. Henry’s law
Which states
that , The mass
of a gas
dissolved in a
given mass of a
solvent at any
temperature is
proportional to
the pressure of a
gas

11. General characteristics of equilibria
involving physical processes
• Equilibrium is possible only in a closed
system at a given temperature.
• Both the opposing process occur at the same
rate and there is a dynamic but stable
condition.
• All measureable properties of the system
remain constant.

12. Equilibriums involving dissolution of
solid or gases in liquids
• Solids in liquids: When no more solute can be
dissolved in the solution it is called saturated
solution.
That is,
Sugar(solution) sugar (solid)
An also the rate of dissolution of sugar =rate of
crystallization of sugar
▪ Gases in liquids: Dissolution of gas in liquid under
pressure in a closed vessel
2 2
▪ CO (g)---<🡪 CO ( in solution

13. Dynamic equilibrium
• When the rates of the forward and reverse
reactions become equal, the concentrations of the
reactants and the products remains constant. This
is the stage of the chemical equilibrium. This
equilibrium is dynamic in nature.
A + B C + D
• The chemical reactions reach a state of dynamic
equilibrium in which the rates of forward and
reverse reactions are equal and there is no net
change in composition
• Eg: N +3H -🡪 2NH
2 2 3

14. Law of chemical equilibrium and
equilibrium constant
• We know that for a reversible reaction:
A + B C+D
these reactants and products are balanced and hence we can relate
them by a equilibrium equation.
Kc=[C][D]/[A][B]
Where kc is called thee equilibrium constant
• At the given temperature, the product of concentrations of the
reaction products raised to the respective stoichiometric
coefficient in the balanced chemical equation divided by the
product of the concentrations of the reactants raised to their
individual stoichiometric coefficients has constant value.
a A + b B cC +d D
Kc=[C]c [D]d /[A]a[B]b

15. What does the value of K
mean?
▪If K>>1, the
reaction is product
–favored, product
predominates at
equilibrium.
▪I f K<<1, the
reaction is
reactant-favored;
reactants
predominant at
equilibrium.

17. Homogeneous equilibrium
• In an homogeneous system the reactants
and products are in the same phase.
and also we can say in the next reaction that
the ions are equal.
CH3COOC2H5(aq) + H2O(aq) CH3COOH(aq) + C2H5OH(aq)

18. Equilibrium in a gaseous system
• We know that p v= n RT
so, p=n/v RT
here p is the pressure in Pascal's, n is the
number moles v is the volume in cubic meter,
and T is the temperature in Kelvin.
if C the concentration in mol/l and p is the bar.
Than p= cRT
Here R=0.0831bar liter/mol K

19. Important features of equilibrium
constant
• Expression of equilibrium constant is applicable only
when concentrations the reactants and products have
attained constant value at equilibrium state.
• The value of equilibrium constant is independent of
initial concentrations of the reactants and products.
• Equilibrium constant is temperature dependent having
one unique value for a particular reaction
• The equilibrium constant for the reverse reaction is equal
to the inverse of the equilibrium constsnt for the forward
reaction

20. Heterogeneous equilibrium
• In a system having more than one
phase is called heterogeneous
equilibrium.
• Example : The equilibrium between
water vapor and liquid in a closed
container is an example of
heterogeneous equilibrium.

21. Applications of equilibrium constant
• Predicting the extent of the reaction: The
magnitude of the equilibrium constant(Kc and Kp
is directly proportional to the concentrations of
the products and inversely proportional to the
concentrations of the reactants.
• If kc.10 is very large than the reaction proceeds
nearly to completion.
• If K is very small then the reaction proceeds rarely.

22. Predicting the directions of the
reaction
• The equilibrium constant helps in predicting the
direction in which a given reaction will proceed at
any stage. For this purpose we calculate the
reaction quotient Q.
• It is denoted with Qc with molar concentrations.
• If Qc> Kc then the reaction will proceed in the
direction of reactants( reverse reaction)
• If Qc< Kc the reaction will proceed in the direction
of products.
• If Qc = kC no net reaction occurs.

24. Calculating equilibrium concentrations
• Write the balanced equation for the reaction.
• Under the equation make the ICE table.
a) the initial concentration.
b)the change in the concentration on going to equilibrium
and
c) the equilibrium concentration.
Substitute the equilibrium concentrations in to the equilibrium
equation and solve for X.
Calculate the equilibrium concentrations from the calculated
value of X.
Check your results by substituting them in to the equilibrium
equation.

25. Relation ship between Equilibrium
constant K, Reaction Quotient Q and
Gibbs energy G
• Δ
G is negative , then the reaction is
spontaneous and proceeds in the forward
direction.
• Δ
G is positive , then the reaction is considered
as non spontaneous and proceeds in the
backward direction.
• Δ
G is 0, reaction achieved equilibrium.

26. A mathematical expression of this
thermodynamic view of equilibrium
can be written as:
Δ
G = Δ
G +RT lnQ
At equilibrium Δ
G =0 and Q=Kc
Then the equation becomes
Δ
G = Δ
G +RT ln K =0
Δ
G =- RT ln K
ln K= ΔG/RT K
= e- Δ
G /RT

27. Factors affecting
equilibria
LeChatelier’s
principle:
Change in any of the
factors that determine
the equilibrium
conditions of a system
will cause the to
change in such
manner so as to
reduce or to
counteract the effect
of the change

28. Effect of concentration change
• Le Chatelier’s principle predicts that:
• The concentration stress of an added
reactant/product is relieved by net reaction in
the direction that consumes the added
substance.
• The concentration stress of a removed
reactant/product is relieved by net reaction in
the direction that replenishes the removed
substance.

29. Effect of the temperature change
• Adjustment in the equilibrium is determined by
whether the reaction is endothermic or
exothermic.
• If the reaction is exothermic, an increase in
temperature shifts the equilibrium toward the
reactants. A decrease temperature shifts reaction
toward the products.
• If the reaction in endothermic, an increase in
temperature shifts the equilibrium toward the
products. a decrease in temp shifts the reaction
towards the reactants.

30. Effect of pressure change
• If the number moles of gaseous products equals the
number moles of gaseous reactants, then pressure changes
have no effect on the equilibrium reaction
• The number of moles of gaseous products is greater than
the number moles of gaseous reactants, then an increase in
pressure shifts the equilibrium towards the reactants. A
decrease in pressure shifts the equilibrium toward the
products.
• If number of moles of gaseous reactants is greater then the
number of moles gaseous products then an increase in
pressure shifts the equilibrium toward the products .a
decrease in pressure shifts the equilibrium toward the
reactants.

31. Effect of the catalyst and inert gases
• A shift does no occur when a catalyst is added
because both forward and reverse rates are
increased equally but equilibrium will be
established faster.
• Adding pure liquid,solidor an inert gas to an
equilibrium. system will not cause a shift.