reaction rates and equillibrium Flashcards
what is a catalyst
a catalyst is a substance which increases the rate of a chemical reaction without undergoing any permanent change itself.
Extra notes on catalysts
The catalyst is not used up in the chemical reaction , the catalyst may react with a reactant to form a intermediate or may provide a surface on which the reaction can take place . At the end of the reaction the catalyst is regenerated .
How do catalysts work
By providing an alternative reaction pathway with a lower activation energy . This means that a greater proportion of the reactant molecules will collide with enough energy to cross the activation energy barrier and react .
What are the two types of catalyst
Homogeneous and heterogeneous catalysts
Is activation energy exo or endo
Activation energy is always endothermic
What is another word for physical state
Phase
What is a homogeneous catalyst
Here the catalyst is in the same physical state as the reactants . The catalyst forms an intermediate which then breaks down to give the product and regenerates the catalyst .
What is a heterogeneous catalyst
Here the catalyst is in a different physical state to the reactants . Heterogeneous catalysts are usually solid in contact with gaseous or aqueous reactants eg. In a vehicle catalytic convertor
What is a heterogeneous catalyst
Here the catalyst is in a different physical state to the reactants . Heterogeneous catalysts are usually solid in contact with gaseous or aqueous reactants . Eg in a vehicle catalytic convertor
What happens in a heterogeneous catalytic converter
Bonds formed to catalyst surface must be weak enough to allow adsorption and desorption to take place , but strong enough to weaken bonds and allow the chemical reaction to take place
What does a poison do
Binds to the surface but doesnt leave
What is a catalytic convertor
Heterogeneous, adsorption/desorption , three key reactions catalysed
What are the three reactions catalysed
The oxidation of carbon monoxide to carbon dioxide .
The reduction of nitrogen monoxide back to nitrogen
The oxidation of hydrocarbons to water and carbon dioxide
What is the equation for the oxidation of carbon monoxide to carbon dioxide
2CO(g) + O2(g) —> 2CO2(g)
What is the equation for the reduction of nitrogen monoxide back to nitrogen
2NO(g) + 2CO2(g) —> N2(g) + CO2(g)
What is the equation for the oxidation of hydrocarbons to water and carbon dioxide
2C6H6+15O2—> 12CO2+ 6H2O
What are the benefits of catalysts
-Lower temperatures and pressures required therefore reducing energy demand .
-different reactions can be used with better atom economy thus reducing waste
-lower production costs
-catalysts can be used to generate specific products
What are some examples of important industrial reactions reliant on heterogeneous catalysts
Making ammonia (Fe) N2+3H2–> 2NH3
Reforming (fuel improvement ) (pt or rh) c6h14 —> c6h12 +h2
Hydrogenation of alkenes (Ni) c2h4 + h2 —> c2h6
Making sulfur trioxide for sulfuric acid (v205) 2So2 + o2 —> 2so3
what is the general reversible reaction equation
aA+bB=cC+dD
what is the general equation for the equilibrium law
Kc = [C]c [D]d
[A]a [B]b
what is Kc in terms of reactants and products
Kc = products
reactants
what is equilibrium law
the exact position of equilibrium is calculated using the equilibrium law
what does the magnitude of Kc indicate
the magnitude of Kc indicates the extent of a chemical equilibrium . it indicates how far a reaction proceeds , not how fast
when K=1 what does this mean
indicates a position of equilibrium that is halfway between reactants and products
