Kinetics - Catalyst Definition of Catalyst + A substance that alters the reaction rate of a particular chemical reaction + chemically unchanged at the.

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Presentation transcript:

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 + How to change the rate of reaction???

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

n For example, Ea for the pathway with catalyst < Ea for the pathway without catalyst

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

Exercise n H 2 and O 2 mixed at room temperature ==> no reaction addition of small amount of Pt powder ==> violent reaction n a) What is the role of Pt? Catalyst n b)What is the effect of Pt on the enthalpy change to the reaction between H 2 and O 2 ? No change

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

Types of Catalyst 1.Heterogeneous Catalyst - catalyst with different phase as the reactant -usually solid state e.g. decomposition of H 2 O 2 with MnO 2 as catalyst e.g. hydrogenation of ethene (Ni as catalyst)

- provides an active reaction surface for reactant ==> reaction occurs with a lower Ea -are usually transition metal such as Pt, Pd, V 2 O 5 and Ni

2.Homogeneous Catalyst -catalyst with the same phase as the reactant -usually in aqueous state e.g. Oxidation of I - ion by S 2 O 3 2- with Fe 3+ ion as catalyst 2I - + S 2 O 8 2- ==> I 2 + 2SO I - + 2Fe 3+ ==> 2Fe 2+ + I 2 2Fe 2+ + S 2 O 8 2- ==> 2Fe SO 4 2-

3. Autocatalysis -the product in the reaction be the catalyst of the reaction -this product is called autocatalyst -e.g.2MnO H + + 5C 2 O 4 2- ==> 2Mn H 2 O + 10CO 2

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? High pressureHigh temperatureHigh Concentration

n Haber Process 3H 2 + N 2 ==> 2NH 3 (Fe) n Contact Process 2SO 2 + O 2 ==> 2SO 3 (Pt/V 2 O 5 ) n Hydrogenation of C=C (hardening of oil - vegetable oil to margarine) CH 2 CH 2 + H 2 ==> CH 3 CH 3 (Ni/Pd/Pt)

B) Catalytic Converters in Car Exhaust Systems +Convert CO, NO x & hydrocarbons to harmless substances  Catalyst are coated on a honeycomb ==> to increase the surface are

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

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

Rhodium Catalyses the reduction of nitrogen oxides and the oxidation of carbon monoxide Rd NO CO N2N2 CO 2

CxHy +O 2 CO 2 +H 2 O CO 2 CO+ O 2 Platinum or Palladium Catalyses the oxidation of CO and hydrocarbons Pt/Pd

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

Further Exercise Download some more exercise from the following web-site