Developing Metals 2: Catalytic Activity Flashcards

1
Q

Definition of catalyst

A
  • Substance which increases the rate of a chemical reaction without undergoing any permanent chemical change its self
  • lowers activation energy and provides an alternative route/pathway
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2
Q

Definition of heterogeneous catalyst

A

Catalyst is in a different physical state to the reactants

eg. Solid catalyst with the reactants in gas liquid or aqueous phase

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3
Q

Definition of homogeneous catalyst

A

Catalyst is in the same physical state to the reactants

eg. All in aqueous solution

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4
Q

Explain how transition metals can act as heterogeneous catalysts ( 3 marker )

A
  1. Transition metals can use d and s electrons
  2. To form weak bonds with reactants
  3. Providing a rate of lower activation energy
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5
Q

What property of transition metals allows them to act as a homogeneous catalysts

A
  • ability to have more than one oxidation state

-act as an intermediary in a redox reaction
speed up reactions involving transfer of electrons i.e. redox reactions

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6
Q

Explain how a transition metal is able to increase the rate of a redox reaction ( I.e. how acts as a homogeneous catalyst ) ( 4 marker )

A
  1. Transition metal ion reacts with one of the reactants ( transition metal reacts to form an intermediate )
  2. Oxidation state of the transition metal ion changes
  3. New iron (intermediate )then reacts to reform ( regenerate ) original transition metal ion
  4. Activation energy for this reaction is lower compared to if the reaction were to happen without the transition metal ion
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7
Q

Give examples of day-to-day situations that involve transition metals acting as heterogeneous catalysts

A
  1. Harber process = iron is catalyst

2. Car exhausts = platinum , rhodium & palladium catalysts

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8
Q

What property allows transition metals to act as heterogeneous catalysts

A

Unfilled d orbitals allows them to accept electrons

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9
Q

Describe the process of heterogeneous catalysis in terms of transition metals ( 4 + 2 internal steps in step 2 )

A
  1. gases adsorbed onto surface of transition metal
  2. Transition metal ions form weak bonds with reactants

= reactants in closer proximity when adsorbed =increase concentration of reactants = increase rate of reaction

= Bonds that form onto the catalyst may withdraw electron density from the molecules internal bonds= weakening them

  1. Products deadsorbed from catalyst surface
  2. Leading active sites available for more gasses ( reactants )
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10
Q

Why is the strength of adsorption essential

A

If bonds to strong
= products remain fixed to catalyst
=prevent further catalysis
= catalyst poisoning

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11
Q

In what other AS topic does homogeneous catalysis occur

A

Ozone = Cl• = catalyst O3 depletion = reactants and catalysts all in gas state = homogeneous

Cl• = regenerated = catalyst

In O3 + Cl• —> ClO• + O2
ClO• + O ——> Cl• + O2

= O3 + O —> 2 O2

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