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Kinetics - Catalyst

Kinetics - Catalyst. Definition of Catalyst. A substance that alters the reaction rate of a particular chemical reaction chemically unchanged at the end of the reaction 2 classes : I) positive catalyst ==> increase the rate II) negative catalyst (inhibitor) ==> decrease the rate

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Kinetics - Catalyst

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  1. Kinetics - Catalyst

  2. Definition of Catalyst • A substance that alters the reaction rate of a particular chemical reaction • chemically unchanged at the end of the reaction • 2 classes : I) positive catalyst ==> increase the rate II) negative catalyst (inhibitor) ==> decrease the rate • How to change the rate of reaction???

  3. By providing an alternative pathway (or mechanism) with lower/ higher activation energy.

  4. For example,Ea for the pathway with catalyst <Ea for the pathway without catalyst

  5. Ea2 • The reaction can then be speeded up by increasing the fraction of molecules that have energies in excess of the Ea for a reaction. Kinetic energy Ea1

  6. Exercise • H2 and O2 mixed at room temperature==> no reactionaddition of small amount of Pt powder==> violent reaction • a) What is the role of Pt? Catalyst • b) What is the effect of Pt on the enthalpy change to the reaction between H2 and O2? No change

  7. What is the effect of Pt on the activation energy of the original pathway? No change • What is the effect of Pt on the activation energy in the reaction? Give another pathway with lower activation energy

  8. Types of Catalyst 1. Heterogeneous Catalyst - catalyst with different phase as the reactant - usually solid state e.g. decomposition of H2O2 with MnO2 as catalyst e.g. hydrogenation of ethene (Ni as catalyst)

  9. - provides an active reaction surface for reactant ==> reaction occurs with a lower Ea - are usually transition metal such asPt, Pd, V2O5 and Ni

  10. 2. Homogeneous Catalyst - catalyst with the same phase as the reactant - usually in aqueous state e.g. Oxidation of I- ion by S2O32- with Fe3+ ion as catalyst 2I- + S2O82- ==> I2 + 2SO42- ------------------------------------------- 2I- +2Fe3+==> 2Fe2+ + I2 2Fe2++ S2O82- ==> 2Fe3++ 2SO42-

  11. 3. Autocatalysis - the product in the reaction be the catalyst of the reaction - this product is called autocatalyst - e.g. 2MnO4- + 16H+ + 5C2O42- ==> 2Mn2+ + 8H2O + 10CO2

  12. High pressure High temperature High Concentration Application of Catalysts A) Usage of Catalysts in Chemical Industries • Cost is always the greatest concerns of manufacturers • How can we get the highest yield of product?

  13. The Cost is Very High!!

  14. Haber Process3H2 + N2 ==> 2NH3 (Fe) • Contact Process2SO2 + O2 ==> 2SO3 (Pt/V2O5) • Hydrogenation of C=C(hardening of oil - vegetable oil to margarine)CH2CH2 + H2 ==> CH3CH3 (Ni/Pd/Pt)

  15. B) Catalytic Converters in Car Exhaust Systems • Convert CO, NOx & hydrocarbons to harmless substances • Catalyst are coated on a honeycomb ==> to increase the surface are

  16. Rhodium (Rd) 3 Kinds of Catalysts: Platinum (Pt) Palladum (Pd)

  17. Air Pollution - Take care our environment - Relief the problem of air pollution Environmental Department Test for the car exhaust

  18. - fermenatation - baking - washing powder contain enzymes Biological Catalysts - Enzymes

  19. Further Exercise Download some more exercise from the following web-site http://nitec.dcu.ie/~chemlc/CAL2.html

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