Homogenous Catalysts

Question 1

Homogenous Catalysts

Answer 1

Catalysts that are in the same physical state as the reactants

Question 2

Usual Form of Homogenous Catalysts

Answer 2

An aqueous catalyst for a reaction between two aqueous solutions

Question 3

Explain how homogenous catalysts work

Answer 3

Work by combining with the reactants to form an intermediate species which then reacts to form the products and reform the product

Question 4

Enthalpy Profile for a Homogenously Catalysed Reaction

Answer 4

Has two humps in it, corresponding to the two parts/steps of the reaction

Question 5

Activation Energy

Answer 5

Ea needed to form the intermediates (and to form the products from the intermediates) is lower than that needed to make the products directly from the reactants

Question 6

What does homogenous catalyst always do?

Explain

Answer 6

Always re-forms.

So it can carry on catalysing the reaction

Question 7

Describe why the reaction between S2O8 2- and I- is slow

Explain how this effects the rate of the reaction?

Answer 7

The redox reaction is slow because both ions are negatively charged.

The ions repel each other, due to the negative charges.

So the ions are unlikely to collide and react due to the reaction having a high activation energy

Question 8

Describe Fe 2+ ions effect on the S2O8 2- and I- reaction

Why does this work?

Answer 8

Fe 2+ ions are oxidised to Fe 3+ ions by the S2O8 2- ions.

The newly formed intermediate Fe 3+ ions now easily oxidise the I- ions to iodine, and the catalyst is regenerated.

Because each stage of the reaction involves a positive and negative ion, so there’s no repulsion

Question 9

Two Equations for the Catalysed Reaction between S2O8 2- and I-

State of all substances

Answer 9

S2O8 2- + 2Fe 2+ –> 2Fe 3+ + 2SO4 2-

2Fe 3+ + 2I- –> I2 + 2Fe 2+

All are aqueous

Question 10

Autocatalysis Reaction

Answer 10

Where a product of a reaction acts as a catalyst

Question 11

Explain how an Autocatalysis Reaction Works

Answer 11

As the reaction progresses and the amount of product increases, the reaction speeds up

Question 12

Describe Mn 2+ ions and their involvement in an autocatalysis reaction

Explain

Answer 12

Mn 2+ is a homogenous catalyst for the reaction between C2O4 2- and MnO4-.

Mn 2+ catalyses the reaction by first reacting with MnO4- to form Mn3+ ions.

The newly formed Mn3+ ions then react with C2O4 2- to form carbon dioxide and re-form the Mn2+ catalyst ions

Question 13

Two Equations for the autocatalysis reaction involving Mn2+ ions

Answer 13

MnO4- + 4Mn 2+ + 8H+ –> 5Mn 3+ + 4H2O

2Mn3+ + C2O4 2- –> 2Mn2+ + 2CO2