Chem5 - Transition Metals - Catalysis

Question 0

Heterogeneous catalyst?

Answer 0

A catalyst in a different phase to the reactants

Question 1

Homogeneous catalyst?

Answer 1

A catalyst which is in the same phase as the reactants

Question 2

Autocatalysis?

Answer 2

When a product of the reaction catalyses the reaction

Question 3

Give an example of autocatalysis by writing half equations and the full redox equation (3)

Answer 3

~ Full redox equation 2MnO4- + 16H+ + 5C2O4^2- –> 2Mn^2+ + 8H2O + 10CO2

~ MnO4^- + 8H+ + 5e- –> Mn^2+ + 4H2O
~C2O4^2- –> 2CO2 + 2e-

Question 4

Give 3 examples of a homogeneous catalyst (3)

Answer 4

~Fe^2+/Fe^3+ in the creation of SO4^2- ~Mn^2+ in the process of making Mn^2+ from MnO4^-
~Cl° free radical in the breakdown of ozone

Question 5

Give 5 examples of a heterogeneous catalyst (5)

Answer 5

~V2O5 in the Contact Process (SO2 –> SO3)
~Cr2O3 in the Synthesis Gas Process (methane and steam by 2 steps becomes ethanol)
~Fe Haber Process creates NH3
~Nickel in the hydrogenation of ethene
~Pt in catalytic converters

Question 6

Write 3 equations to explain the Contact Process

Answer 6

~Overall 2SO2 + O2 –> 2SO3
~with catalyst: SO2 + V2O5 –> SO3 + V2O4
~Catalyst reforms: V2O4 + O2 –> V2O5

Question 7

Write 2 equations to explain the Synthesis Gas process, name the catalyst for this process (3)

Answer 7

Methane and Steam!

~CH4 + H2O –> CO + 3H2
~CO + 2H2 –> CH3OH

~catalyst: Cr2O3

Question 8

Explain what Hydrogenation is, what its used for and name the catalyst used (3)

Answer 8

~ethene reacts with H2
~used to make margerine (thicker at lower temp, not liquid)
~catalyst is nickel

Question 9

Give the 3 steps of how a heterogeneous catalyst functions (1)

Answer 9

~reactants adsorbed onto active sites of catalyst (weaken bonds, more favourable orientation)
~reaction takes place
~products are desorbed

Question 10

State a metal with a low catalytic efficiency which is used to slow reactions down, explain why it is this way (3)

Answer 10

~Ag (silver)
~low adsorption
~reactant isn’t adsorbed onto the active site long enough for a reaction to take place

Question 11

State an inefficient catalyst that has too high an adsorption, state why this makes it inefficient (3)

Answer 11

~W (tungsten)
~reactants cannot move around surface
~cannot desorb from W

Question 12

Explain what makes an efficient catalyst (1)

Answer 12

When ease of adsorption (not too weak) and desorbtion (not to strong) balance out

Question 13

When Iodide and S2O8^2- react they react very slowly, explain why, state what catalyst is used for this reaction and write the half equations (involving the catalyst) and overall equation (5)

Answer 13

~both ions are negatively charged and repel each other
~Fe^2+/Fe^3+

Half equations:

~2Fe^2+ + S2O8^2- –> 2Fe3+ + 2SO4^2-
~2Fe^3+ + 2I^- –> 2Fe^2+ + I2

Overall equation:

S2O8^2- + 2I^- –> 2SO4^2- + I2

Question 14

Give 2 steps of how a homogenous catalyst functions (2)

Answer 14

~catalyst reacts with reactant to form an intermediate

~intermediate reacts to form products faster, catalyst is reformed in this reaction and the products made

Question 15

describe two different measures which maximise the efficiency and minimise the cost associated with expensive heterogeneous catalyst (2)

Answer 15

~increase surface area

~remove catalyst poisons from the reactants

Question 16

In catalytic convertors state the catalyst used, the reaction which takes place and the reducing agent used (3)

Answer 16

~Platinum (Pt)
~2NO + 2CO –> 2CO2 + N2
~reducing agent: CO