Chemical Equilibrium
2HI(g)
Ex 1. For the equilibrium: H 2(g) + I2(g)
the equilibrium constant Kc is 50.5 at 448oC.
If [H2]o = [I2]o = 1mol.L-1,what will the concentration of H2, I2 and HI be at equilibrium.
Ex 2. Consider the following reversible reaction:
PCl5(g)
PCl3(g) + Cl2(g)
One mole of PCl5 is placed in a flask of capacity 4 liter to be dissociated at constant temperature
T. the number of moles of Cl2 formed at equilibrium is 0.25mole.
Calculate the equilibrium constant of the above system at temperature T.
Ex 3. At 100oC, the equilibrium constant for the reaction system,
COCl2(g)
CO(g) + Cl2(g)
is Kc = 2.19x10-10
1. Determine whether the following mixture of components of the above system is at
equilibrium:
[COCl2] = 3.5x10-3 mol.L-1
[CO] = 1.2x10-5 mol.L-1
[Cl2] = 3.3x10-6 mol.L-1
2. If it is not at equilibrium, in what direction the system proceeds to reach equilibrium?
Ex 4. In a closed container of volume V and at constant temperature T = 300K, we introduce 2 mol of
NO and 1 mol of O2 gases. the following equilibrium is established:
2NO 2(g)
2NO(g) + O2(g)
Calculate the degree of conversion (α) of NO if the amount of NO2 at equilibrium is three time
that of O2.
Ex 5. Ethanamine C2H5NH2 gas is put in an empty flask of volume V= 2L, maintained at constant
temperature T = 500K.
The following equilibrium is established:
C2H 5NH 2(g)
C2H 4(g)
+
NH 3(g)
The initial amount of ethanamine is 0.2 mol and the total amount of the mixture at equilibrium is
0.3 mol.
1. Calculate the degree of dissociation α of ethanamine.
2. Calculate the equilibrium constant Kc at 500K.
Ex. 6
Decomposition of SO2Cl2
A closed bottle of volume V=1L contains SO2Cl2 (g) in a solution of concentration 0.04mol.L-1 at
temperature T=27Cº and pressure P=1 atm where the molar volume of the gas is Vm = 24L.mol-1
1. Prove that the number of mol of SO2Cl2 (g) is n0= 0.04 mol
2. When the temperature in the bottle increases to T=227Cº, A chemical equilibrium is established.
The equation of decomposition of SO2Cl2 (g ) is:
The total amount of gases at equilibrium is ne = 0.05mol.
Let α be the degree of conversion of SO2Cl2 at equilibrium.
2.1. Express the amount of each gas at equilibrium in term of α. Give the value of each.
2.2. Express the equilibrium constant at equilibrium in term of α. Give its value.
Ex. 7
Formation of Sulfur trioxide
A gaseous mixture of 0.8 mole of SO2 and 0.5 mole of O2, is held in a flask of volume 2L and at
temperature 298K. When equilibrium is attained, it’s found that the number of mole of SO3 is triple that
of O2
The reaction is given by the following equation:
2SO2(g) + O2(g) ⇌ 2SO3(g)
Let α be the degree of conversion of O2.
1. Study of the system at Equilibrium
1.1. Recopy and complete the following table in terms of x ( x : is the number of moles of O2
dissociated)
SO2
O2
SO3
Initial State
Equilibrium state
1.2. Determine the composition of the equilibrium mixture.
1.3. Write the expression of the equilibrium constant Kc then show that its value is 90.
1.4. Calculate the degree of conversion of oxygen. .
2. Equilibrium and thermal nature:
In another experiment at temperature 298K, the concentrations at instant (t) are found to
be: [SO3] = 0.15 mol/L
[SO2] = 0.2 mol/L
[O2] = 0.1 mol/L
2.1. Discuss if the system is at equilibrium.
2.2. If it is not at equilibrium, what direction does the reaction favor to achieve equilibrium?
2.3. At T = 50K , α = 1 . What conclusion can you draw? Justify.
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Ex. 8
Study of Equilibrium Reaction
Ethanol is a chemical compound of great industrial and commercial importance. It is used in many chemical
reactions and also utilized as an intermediate for the synthesis of several chemical compounds.
1. Industrial Preparation of Ethanol
A gaseous mixture of molar composition of 40% of ethene and 60% of water vapor is introduced in an industrial
production unit, maintained at temperature 300 oC, at volume V and under pressure P = 70 atm.
A chemical equilibrium is established according to the following equation:
𝐶2 𝐻4(𝑔) + 𝐻2 𝑂(𝑔) ⇌
𝐶2 𝐻5 𝑂𝐻(𝑔)
The equilibrium constant of this reaction at 300 oC is Kc 1.54x10-3
1.1. Copy and complete the following table in terms of n and α where α is the degree of conversion of ethene
to ethanol.
Compounds
Initial state (in mol)
C2H4
H2O
2n
4n
C2H5OH
Equilibrium state (in mol)
1.2. Write the expression of Kc at 300 oC in terms of n, α and V.
2. Production of Ester
no mol of ethanol reacts with no mol of ethanoic acid to
produce ester and water in the presence of few drops of
sulfuric acid.
The following is the equation of the reaction:
𝑒𝑡ℎ𝑎𝑛𝑜𝑙 + 𝑒𝑡ℎ𝑎𝑛𝑜𝑖𝑐 𝑎𝑐𝑖𝑑 ⇌ 𝑒𝑠𝑡𝑒𝑟 + 𝑤𝑎𝑡𝑒𝑟
The number of moles of ester formed at each instant is
recorded and the following graph is drawn:
2.1. Draw out from the graph a characteristic of this
reaction.
2.2. Knowing that Kc = 4, determine the value of no.
Ex. 9
Esterification Reaction
Ethyl acetate, an ester of the molecular formula (C4H8O2) is used as a solvent. It is present in confectionery,
perfumes, and fruits. In perfumes, it evaporates quickly, leaving only the scent of the perfume on the skin..
Ethyl acetate is prepared using the alcohol ethanol (C2H6O) and the carboxylic acid ethanoic acid (C2H4O2)
according to the following equation:
𝐶2 𝐻4 𝑂2(𝑙) + 𝐶2 𝐻6 𝑂(𝑙) ⇌ 𝐶2 𝐻8 𝑂2(𝑙) + 𝐻2 𝑂(𝑙)
Given:
The molar mass in g.mol-1 : Ethanoic acid - 60, ethanol – 46.
The density in g.ml-1 : Ethanoic acid is d1 = 1.05 and ethanol is d2 = 0.789
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1.
The Dynamic Equilibrium.
2no mol of Ethanoic acid and no mol of ethanol are introduced into a round-bottomed flask in the presence of few
drops of sulfuric acid H2SO4; the reaction mixture is heated at constant temperature T 1. Let α be the degree of
transformation of Ethanol (C2H6O).
1.1. Complete the following table in terms of no and α.
Species
Initial State (mol)
Equilibrium state (mol)
C2H4O2
2no
C2H6O
no
C4H8O2
H2O
∝2
1.2. Show that the equilibrium constant is expressed by 𝐾𝐶 = (2−∝)(1−∝)
2.
Study of the Reaction Mixture
Let V1 and V2 be respectively, the volumes (in mL) of pure ethanoic acid and pure ethanol added to the round
bottom flask at t = 0 min.
To study the amount of Ethanoic acid at each instant t, a sample of the reaction mixture was titrated with sodium
hydroxide solution (Na+ , HO-). Before titration, the sample was added into a beaker containing very cold distilled
water.
The following document shows the curve studying the
variation of the number of moles of Ethanoic acid verses
time n(Ethanoic acid) = f(t).
2.1. Specify the role of adding the sample into cold distilled
water. Indicate the kinetic factors involved in this step.
2.2. Draw out, from the graph:
2.2.1. one characteristics of this reaction.
2.2.2. the instant at which dynamic equilibrium is
reached.
2.3. Determine the relation between V1 and V2.
2.4. Determine the value of α. Deduce the value of Kc.
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