Catalysts Flashcards
Catalysts
Do they change the position of equilibrium?
No
What is a heterogenous catalyst?
Where does the reaction usually happen for a heterogenous catalyst?
In different phase
Surface of catalyst at active site
How do you increase efficiency of a catalyst?
How do you do this?
Increase SA
Use thin foil instead of lump
Impregnate on ceramic material eg silica or asbestos
What is the difference between absorption and adsorption?
Where on the catalyst are the reactants adsorbed?
How do reactants become more reactive?
Do both reactants have to be attached to the catalyst?
What makes a good adsorber?
Why is silver not?
Why is tungsten not?
Absorption taken up adsorption stick to Surface at active site Bonds weakened No one can hit the other Doesn't hold on to strong or release too easy Releases too easy Hold on to strong
What is catalyst poisoning?
When something attaches to catalyst preventing the reactants adsorbing
Catalytic converter What catalysts can be used? How is their SA increased? What are they poisoned by? Why may catalyst break down occur? What's the equation for this process?
Pt,Pd,Rh Spread on ceramic honeycomb Lead Catalyst becomes separated from support medium 2CO+2NO-->2CO2+N2
Haber Process What's the catalyst? What's the equation? What poisons it? How do we prevent them poisoning it? What is H2O present in? How often does it have to be replaced?
Fe N2+3H2-->NH3 CO,CO2,H2O Remove from feedstock gases Natural gas Every 5 anos
The contact process What is it he production of? What's the catalyst? What part of the reaction does this catalyse? What's the equation for this? What does the SO3 then react with? What does the catalyst do to the SO2?
H2SO4 V2O5 SO2+1/2O2-->SO3 SO2+V2O5-->SO3+V2O4 V2O4+1/2O2-->V2O5 H2O Oxidises it
Manufacture of methanol
what’s the catalyst?
What are the equations for the reaction?
What is it widely catalysed by?
What are over 30 million tonnes of it used for a year?
Cr2O3 CH4+H2O--> CO +3H2 CO+2H2--> CH3OH Cu,ZnO,Al2O3 Make plastics
What is a homogenous catalyst?
What does a homogenous catalyst usually involve the formation of?
Same phase
An intermediate
Oxidation of iodide by peroxodisulphate ions
What is the catalyst?
What is the half equation for:
Oxidation of iodide
Reduction of S2O82-
What is the overall equation?
What does the iodide do to the iron?
What does the S2O82- do to the iron?
What are the equations for this?
Why is this reaction otherwise slow?Fe2+
2I- –> I2+2e-
S2O82- +2e- –> 2SO42-
2I-+S2O82- –> I2+2SO42-
Reduces
Oxidises
S2O82-+2Fe2+ –> 2SO42-+2Fe3+
2Fe3+ + 2I- –>2Fe2+ +I2
Because the reactants are both negatively charged
Autocatlysis by Mn2+
What colour is KMnO4?
What is it run from the burette into?
When does the purple colour begin to decolourise? When does it decolourise til?
Half equation of MnO4- to Mn2+
Half equation of C2O42- to CO2
Overall equation
Why does the fact that the reactants are negatively charged mean a slow reaction?
What is the autocatalyst?
Half Equation of Mn2+ con MnO4-
What does the Mn3+ react with?
EquationPurple Hot sol containing C2O42- On further addition of the oxidant Until the end point MnO4-+8H+ +5e- > Mn2+ +4H2O c2O42->2CO2+2e- 2MnO4-+16H++2C2O4->2Mn2++8H2O+10CO2 Less likely to collide with sufficient energy to react 4Mn2+ +MnO4-+8H+ > 5Mn3+ +4H2O Ethandioate ions Mn3++C2O42->2CO2+2Mn2+
