Catalysis |
| This is another very active area in chemical kinetics. We need to be in the look out for better catalysts in petrochemical, polymer and pharmaceutical industry because more efficient and less degradable catalysts save crores of rupees. A catalyst enhances the reaction rate without taking part in the reaction stoichiometry. This enhancement is usually done by reducing the activation energy. Enzymes or biocatalysts play a critical role in metabolism. For example, the activation energy for the hydrolysis of sucrose in 107 kJ/mol. The enzyme saccarase reduces this to 36 kJ/mol, enhancing the hydrolysis rate by a factor of 1012 at the body temperature! Without this, we may be unable to digest sugar all our life!. |
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| A heterogeneous catalyst is in a phase different from the reacting medium. (e.g., a solid or a powder catalyzing a gas phase reaction). A homogeneous catalyst is in the same medium as the phase of the reaction mixture. |
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| Hydrogenation of ethylene can be catalysed by several powdered metals. The mechanism of the reaction has been shown to be different in the presence of different metal catalysts and three such experimental findings are shown below |
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C 2 H 4 + H 2  C 2 H 6 |
(30.31) |
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| d [ C2H6 ] /dt = k1 [ H2 ] [ C2H4 ] / ( 1 + K1 [ C2H4 ] )2 |
(30.32) |
| (copper powder catalyst) |
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| d [ C2H6 ] /dt = k2 [ H2 ] [ C2H4 ] / (1 + k 2 [ C2H4 ] ) |
(30.33) |
| (nickel surface catalyst) |
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| d [ C2H6] / dt = k3 [ H2 ] 1/2 [ C2H4 ] |
(30.34) |
| (iridium powder / film catalyst) |
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