Catalysts Flashcards
What is a catalyst?
a substance that speeds up a reaction and is not itself consumed (remains chemically unchanged)
How do catalysts speed up reaction rates?
they provide an alternate route from reaction to product which has lower activation energies
Name 2 pros of heterogenous catalysts
– Relatively inexpensive
– Easily separate catalyst from the solution of products by filtration or decanting
Name a con of heterogenous catalysts
Not well understood as most advanced techniques cannot be used to measure solids (insoluble) in reactions
What is the difference between a heterogeneous and homogeneous catalyst
the heterogenous catalyst is a different phase than the reactants where as the homogenous catalyst is the same phase as the reactants
What type of susbtance are homogenous catalysts usually?
metal complexes (organometallic complexes)
Name 3 pros of homogenous catalysts
– rates are usually high (less restricted by diffusion)
– All molecules take part in catalysis (not just surface as in homogeneous)
– Easier to study, better understood which allows for guided improvement
Name a con of homogeneous catalysts
Separation and reuse of catalysts is difficult/impossible/expensive
Given an example of a hetergenous catalyst and what it is used for
zeolites (aluminosilicates) in cracking of oil
Given an example of a homogenous catalyst and what it is used for
[RhCl(PPh3)3] used in homogeneous catalysis of alkene hydrogenation
What type of compound are organometallic compounds?
coordination compound
Give two examples of metal alkyls
Pb(C₂H₅)₄ tetraethyllead
Hg(CH₃)₂ dimethylmercury
What type of bonding do metal alkyls have?
Simple overlap of orbitals to form σ (sigma) bonds
Given three examples of metal carbonyls
Cr(CO)₆
Fe(CO)₅
Ni(CO)₄
Metals can form σ and π bonds with CO ligand because…. (called back donation or back bonding)
C in CO has empty orbitals that accepts electrons from the metal
