ER10b Catalyst Note and Questions.pdf - SCH4U1 ER10 CATALYSTS A catalyst is a substance which speeds up a reaction without being used up itself It

ER10b Catalyst Note and Questions.pdf - SCH4U1 ER10...

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SCH4U1 ER10 CATALYSTS A catalyst is a substance which speeds up a reaction without being used up itself. It speeds up the reaction by changing the reaction mechanism to one which requires less activation energy. The actual mechanisms of some catalytic reactions are not well understood. However, many are understood and these can be grouped into two general categories: Heterogeneous Catalysts Heterogenous catalysts are in a different phase than the reactants. Some solid catalysts are classified as surface catalysts because they have large surface areas and are capable of adsorbing the reactants on their surfaces which makes it easier for the reaction to occur. Adsorption refers to the binding of molecules to a surface, in contrast to absorption which refers to the uptake of molecules into the interior of another substance. In other cases, one of the reactant molecules may readily react with the atoms of the catalyst and form an intermediate species which undergoes subsequent reactions. This results eventually in the formation of the desired products and the regeneration of the catalyst. Platinum Catalyzed Formation of CO 2 From CO and O 2 Pt 2CO + O 2 2CO 2 Platinum acts as a surface catalyst when increases the rate of formation of carbon dioxide from carbon monoxide and oxygen. Mechanism of a Heterogeneous Catalyst: Platinum and nickel are used to catalyze hydrogenation reactions. These reactions convert unsaturated hydrocarbons and fats into saturated compounds by adding two hydrogens across the double bond. For example, the hydrogenation of ethene: Pt CH 2 =CH 2 + H 2 CH 3 -CH 3 1) The hydrogen reaches the solid platinum and is adsorbed onto it. This creates a reactive intermediate of hydrogen on the catalyst itself.
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  • Fall '16
  • Maheshwari
  • Chemistry, Hess Law, Thermochem

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