Catalysts Quiz: Chemical Reactions and Rate of Reaction

Study Notes

Catalysts and Rate of Reaction

Activation energy (Ea) is 245 kJ mol-1 for uncatalysed reactions and 121 kJ mol-1 for catalysed reactions.
Catalysts have a big effect on the rate of reaction.

Types of Catalysts

Homogeneous catalysts: reactants and catalyst are in the same phase (e.g., gas/gas or liquid/liquid).
Heterogeneous catalysts: reactants and catalyst are in different phases (e.g., liquid/gas, solid/gas, or solid/liquid).

Advantages and Disadvantages

Homogeneous catalysts:
- Can control concentration precisely.
- Difficult to remove catalyst.
Heterogeneous catalysts:
- Can be easily filtered away from the reaction mixture.
- Can be poisoned by substances binding to active sites.

Heterogeneous Catalysts

The catalyst must adsorb the reactant strongly enough to enable it to react.
The catalyst must allow the product to desorb, otherwise, the active sites will become blocked.

Transition Metal Catalysts

Transition metals are good redox catalysts because they have variable oxidation states and can be repeatedly oxidized and reduced.

Increasing the Rate of Reaction

Requirements for a reaction to take place:
- Particles collide.
- Particles collide with sufficient energy to react.
- Particles collide with the correct orientation.
Ways to increase the rate of reaction:
- Increase concentration.
- Increase pressure.
- Increase surface area.
- Stir the solution.
- Increase temperature.
- Add a catalyst.

Effect of Catalysts

A catalyst provides an alternative route for the reaction with a lower activation energy.
A catalyst does not lower the activation energy.
A catalyst can:
- Increase the rate of the reaction.
- Increase the probability of a successful collision.
- Increase the rate constant for a reaction.
- Help the system reach equilibrium more rapidly.

Rate Equations

The rate equation gives information about how a reaction takes place and the most efficient method of increasing the rate of reaction.
The overall order of the reaction is found by adding up the individual orders with respect to all reactants.

Determining the Order of a Reaction

To determine the order of a reaction, you need to measure the rate of reaction and see how it changes as you alter the concentration of each reagent.
Applications:
- Working out how a reaction takes place (e.g., within the body).
- Finding the best way to optimize a reaction (e.g., industrially).
- Determining how much time has passed since a reaction started.

Description

Explore the role of catalysts in chemical reactions and how they affect the activation energy and reaction rate. Learn about the differences between catalysed and uncatalysed reactions, and the impact of catalysts on the reaction pathway.