AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
Transition metals and their compounds can act as heterogeneous and…
Full specification wording
Catalysts (A-level only): Transition metals and their compounds can act as heterogeneous and homogeneous catalysts.
A catalyst provides an alternative route with a lower activation energy and is chemically unchanged at the end of the reaction.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 1 of 7
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A catalyst provides an alternative route with a lower activation energy and is chemically unchanged at the end of the reaction. Transition metals are unusually good at this for one reason: variable oxidation states let them accept electrons from one reactant and pass them to another, changing state temporarily and then changing back. Heterogeneous examples, where the catalyst is in a different phase, include iron in the Haber process, vanadium(V) oxide in the Contact process, nickel in hydrogenation, and platinum with rhodium in catalytic converters. Homogeneous examples, where catalyst and reactants share a phase, include Fe²⁺ catalysing the reaction between S₂O₈²⁻ and I⁻, and Mn²⁺ autocatalysing the reaction between MnO₄⁻ and C₂O₄²⁻.
What earns the marks
- Defining a catalyst as providing an alternative route of lower activation energy.
- Stating that the catalyst is chemically unchanged at the end of the reaction.
- Classifying a named example correctly as heterogeneous or homogeneous.
- Linking catalytic ability to the metal's variable oxidation states.
Common mistakes and how to put them right
Saying a catalyst lowers the activation energy of the reaction rather than offering a route with a lower one.
Claiming the catalyst takes no part in the reaction at all, rather than being used and regenerated.
Stating that a catalyst shifts the position of an equilibrium instead of reaching it faster.
Classifying vanadium(V) oxide in the Contact process as homogeneous because the gases pass over it.
Exam tips
- Write both halves of the definition: an alternative route, and a lower activation energy.
- Name the phases of catalyst and reactants when classifying, rather than just asserting the label.
- If asked why transition metals catalyse reactions, go straight to variable oxidation states.
Try the lesson
The start of the Catalysts (A-level only): Transition metals and their compounds can act as heterogeneous and homogeneous catalysts. lesson, made from checked teaching notes for this specification point.
Have a go first
Which statement describes a heterogeneous catalyst?
Listen
A catalyst provides an alternative route with a lower activation energy and is chemically unchanged at the end of the reaction. Transition metals are unusually good at this for one reason: variable oxidation states let them accept electrons from one reactant and pass them to another, changing state temporarily and then changing back. Heterogeneous examples, where the catalyst is in a different phase, include iron in the Haber process, vanadium(V) oxide in the Contact process, nickel in hydrogenation, and platinum with rhodium in catalytic converters. Homogeneous examples, where catalyst and reactants share a phase, include Fe²⁺ catalysing the reaction between S₂O₈²⁻ and I⁻, and Mn²⁺ autocatalysing the reaction between MnO₄⁻ and C₂O₄²⁻. A strong answer earns marks for these points. defining a catalyst as providing an alternative route of lower activation energy. stating that the catalyst is chemically unchanged at the end of the reaction. classifying a named example correctly as heterogeneous or homogeneous. linking catalytic ability to the metal's variable oxidation states. Exam tip: Write both halves of the definition: an alternative route, and a lower activation energy.
Key words
Say what each word means before you turn the card.
catalyst
Try answering aloud or in your head before turning the card.
heterogeneous catalyst
Try answering aloud or in your head before turning the card.
homogeneous catalyst
Try answering aloud or in your head before turning the card.
See every definition
- catalyst
- Provides an alternative route with a lower activation energy and is chemically unchanged at the end of the reaction.
- heterogeneous catalyst
- A catalyst that is in a different phase from the reactants.
- homogeneous catalyst
- A catalyst that shares a phase with the reactants.
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Catalysts (A-level only): Transition metals and their compounds can act as heterogeneous and homogeneous catalysts.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge