6.2.7 Catalysis Flashcards
1
Q
What is a heterogenous catalyst?
A
- Different physical state to reactants
- Reaction occurs at active sites on surface of catalyst
- Eg. Fe in the Haver process making ammonia
2
Q
What are homogenous catalysts?
A
- Catalysts in the same physical state as the reactants
3
Q
How do vacant d-orbitals contribute to catalysis?
A
- Vacant d orbitals are energetically accessible
- Attractions can be formed between transition metal and pairs of electrons on small molecules
- Eg. Hydrogen
- So these orbitals can be filled by donating pairs of electrons
4
Q
How can the efficiency of the use of catalysts be increased?
A
- Increasing the SA of the catalyst
- Coating an inert surface medium with the catalyst to avoid using lots of the catalyst (decreases expenses) (can be by spreading catalyst over hollow mixture such as honeycomb)
5
Q
Which metal is used for catalytic converters?
A
Platinum or rhodium
6
Q
What is the contact process?
A
- Manufacture of sulphuric acid
7
Q
What is the haber process?
A
- Production of ammonia
- N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
- Iron pellets as heterogenous catalyst
8
Q
How does iron act as a catalyst in the haber process?
A
- Pellets provide large SA
9
Q
What are some limitations of heterogenous catalysts?
A
- Don’t last forever, impurities can become lodged to the surface preventing binding and further catalytic reaction
- Wears away, only thin layer over support medium
- Do not work as well at low temperatures (short car journeys still pollute then coz catalytic converters take 15 mins to start working properly)
10
Q
How do variable oxidation states contribute to catalysis?
A
- Transition metals can be excellent catalysts
- They can accept and lose electrons by jumping from one oxidation state to another
- Oxidising and reducing agents
11
Q
How does Fe(II) catalyse the reaction between I- and S2O8 2-?
A
12
Q
What is autocatalysis?
A
- Where the product acts as a catalyst
13
Q
How does the reaction between manganate (VII) ions and oxalate ions work?
A
- autocatalysed reaction
- Product (Mn (II)) is a catalyst
- So reaction speeds up as more Mn (II) is forced
