Catalysis Flashcards

1
Q

What is a catalyst?

A

speeds up a chemical reaction by providing an alternate reaction pathway with lower activation energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why are there more successful collisions in the presence of a catalyst?

A

a greater proportion of reactant particles will have energy that is above the lowered activation energy
-increase in percentage of successful collisions, so increase in rate of reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is a heterogeneous catalyst?

A

a catalyst that acts in a different phase to the reactants. occurs on surfaces

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is a homogeneous catalyst?

A

a catalyst that acts in the same phase to the reactants. occurs through an intermediate species

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How do heterogeneous catalysts work?

A

-surface of solid catalyst
-when a reactant approaches the solid there is a tendency for them to react, forming weak temporary bonds - adsorption
1- adsorption of a reactant
2- reaction
3- desorption of a product

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Name three things that could happen as a result of adsorption

A

-reactant more likely to collide with another reactant, increasing collision frequency
-reactant held in a more favourable configuration so activation energy is decreased
-reactant may undergo internal bond breaking/rearrangement, so the reactive fragments react more readily/AE is lowered

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the heterogeneous catalyst in the Haber process?

A

Fe

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the heterogeneous catalyst in the Contact process?

A

V2O5

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What happens when the adsorption is too strong?

A

-keeps molecules immobile
-fails to regenerate active sites
-poisoned by the product

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What happens when the adsorption is too weak?

A

reactants aren’t encouraged to come together and aren’t given a good opportunity to react with each other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How is the cost of catalysts reduced?

A

expensive catalysts are spread very thinly onto an inert support medium in order to increase the surface to mass ratio

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the impact of impurities on a catalyst?

A

blocks the active sites, reducing the efficiency of the catalyst and increases the cost of the process

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What poisons the iron catalyst in the Haber process?

A

sulphur impurities

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the equation for the Contact process?

A

2SO2(g) + O2(g) ⇌ 2SO3(g)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Explain the Contact process

A

1) SO2 diffuses onto the catalyst surface and a redox reaction occurs
V2O5(s) + SO2(g) –> V2O4(s) + SO3(g)

2) vanadium oxide(IV) formed then reacts with oxygen to regenerate vanadium (V) oxide
2V2O4(s) + O2(g) –> 2V2O5(s)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the overall equation for the oxidation of iodide ions by peroxodisulphate ions and the two steps that can occur in any order?

A

overall:
S2O8 2- + 2I- –> 2SO4 2- + I2

two steps:
2Fe3+ + 2I- –> 2Fe2+ + I2
2Fe3+ + S2O8 2- –> 2Fe3+ + 2SO4 2-

17
Q

What is autocatalysis?

A

where the product of a particular reaction catalyses the reaction

18
Q

What is the overall equation for the reaction between ethanedioate ions and manganate(VII) ions?

A

2MnO4- + 16H+ + 5C2O4 2- –> 2Mn2+ + 10CO2 + 8H2O

19
Q

Why is the reaction between C2O4 2- and MnO4 - so slow?

A

both negative ions and so they repel

20
Q

Describe how autocatalysis is involved in the reaction between C2O4 2- and MnO4 -?

A

-Mn2+ ions act as an autocatalyst
-they react readily with the MnO4- ions to make Mn3+ ions
4Mn2+ + MnO4- + 8H+ –> 5Mn3+ + 4H2O
-these can then react with C2O4 2- ions to regenerate Mn2+ ions
2Mn3+ + C2O4 2- –> 2CO2 + 2Mn2+

21
Q

Why does the colour change from purple to colourless not happen straightaway?

A

-rate of reaction is initially slow
-as some Mn2+ ions start to form, further addition of the potassium manganate(VII) leads to rapid decolourisation
-until the light pink end point is reached

22
Q

What is the half equation for the reaction of potassium manganate ions?

A

MnO4- + 8H+ + 5e- –> Mn2+ + 4H2O

23
Q

What makes an appropriate acid?

A

-strong -goes brown if there is not an excess of H+
-not an oxidising agent
-not a reducing agent

DILUTE SULPHURIC ACID

24
Q

How do you do redox titration calculations?

A

-calc the moles of manganate or dichromate using mol = conc x vol
-use molar ratios for finding out moles of Fe2+ (x5 for Mn, x6 for Cr)
-calc mass of Fe2+ present - 55.8 x moles Fe2+
-calc % by mass by doing mass Fe2+ / mass of sample x100