CATALYSIS
The term catalysis is
given by Berzelius.A catalysis is a substance which alter the rate or
reaction.The catalysis does not alter in the reaction and is removed as such
after the completion of the reaction.
Catalysis is the process of increasing the rate of
a chemical reaction by adding a substance known as a catalyst, which is not
consumed in the catalyzed reaction
and can continue to act repeatedly.
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| CATALYSIS |
GENERAL CHARACTERISTICS OF CATALYSTS
A
catalyst remains unchanged in mass and chemical composition.
Only
a very small amount of catalyst is sufficient to catalyze a reaction.
A
catalyst does not initiate a reaction.
A
catalyst does not change the equilibrium state of a reversible reaction as it
increases the rate of forward as well as backward reaction.
ENZYME CATALYSIS
The
increase in the rate of reactions by the enzyme is known as enzyme catalysis.
Enzymes
are biocatalysts and all are protein in nature.
Enzymes
are highly specific in their nature.
Enzymes
are highly sensitive to temperature i.e., the temperature at which enzymes are
maximum active,varies between 25-370 C.
The
rates of enzymatic reactions are very much affected by pH change.
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ENZYME CATALYSIS
SOME IMPORTANT PROCESSES AND CATALYST USED
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PROCESS
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CATALYST
USED
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Manufacture of ghee from vegetable
oils
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Nickel
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Haber’s process for the
manufacture of ammonia
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Fe (here Mo acts as activator)
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Contact process for the
manufacture of sulphuric acid
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Pt powder
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Conversion of proteins into
peptide
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Pepsin enzyme
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Conversion of proteins into amino
acids
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Erepsin enzyme
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Conversion of glucose into ethanol
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Zymase enzyme
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Conversion starch into maltose
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Diastase enzyme
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Formation of vinegar from cane
sugar
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Micoderma aceti
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Conversion of sucrose into glucose
and fructose
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Invertase enzyme
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Conversion of milk into curd
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Lactase (lactobacilli)
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Ostwald’s process for the
manufacture of HNO3
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Platinum (Pt)
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GASEOUS STATE
At STP/NTP, temperature,
T= 273.15 K, pressure,p = 1 atm = 101.35 kPa, volume,V = 22.41 mol-1
BOYLE'S LAW
At
constant temperature, the volume of a gas is inversely proportional to its
pressure.
V∝ 1/p [at constant temperature ]
i.e., p1V1 = p2V2
CHARLES LAW
At constant pressure,
volume is directly proportional to absolute temperature.
V ∝ T [at constant pressure]
V1/T1 =V2/T2
GAS EQUATION
This express a relation
between pressure, volume and temperature of a gas.
V ∝
1/P (Boyle's law)
V ∝ T
(Charles law)
on combining
V ∝ T/p or pV/T = R
or
pV = RT
(Where, R = gas constant)
This is ideal gas
equation,
For n moles, pV = nRT
Value of gas constant, R
depends upon the units of measurements.
R = 0.0821 L atm mol-1 K-1
=8.3143 J mol-1 K-1
=5.189* 1019 eV mol-1 K-1
= 1.99 cal mol-1 K-1
Gas constant, R for a
single molecule is called Boltzmann constant (K)
Density of a gas is
proportional to pressure and inversely related to temperature
i.e.,
d = pM/RT
EQUILIBRIUM
When a reversible
reaction is performed in a closed container, a state is reached when the rate
of forward and backward reactions become equal.This state is called chemical
equilibrium
Chemical equilibrium is
dynamic in nature and in a reversible reaction it can be approached from either
of sides.Catalyst has no effect on the state of equilibrium.
Free energy change(ΔG0)
at equilibrium is zero.
At equilibrium, the
concentrations do not change with time.
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