Catalysts
Catalysts
- A catalyst speeds up a reaction but is not used up.
- It works by giving a new route with a lower activation energy.
- It does not change the enthalpy of the reaction.
Practice
A catalyst speeds up a reaction by:
A catalyst offers a new mechanism with a lower Eₐ, so more molecules can react; it is not used up.
How a catalyst works
- A catalyst provides a different reaction mechanism with a lower $E_A$.
- On the Boltzmann distribution, lowering $E_A$ moves the line left, so more molecules can react → more effective collisions → faster rate.
- The enthalpy change $\Delta H$ is unchanged — only the activation energy is lowered.
Practice
A catalyst does NOT change the:
A catalyst lowers Eₐ and speeds the rate, but the overall ΔH (reactants to products) is unchanged.
Two types
- a homogeneous catalyst is in the same physical state as the reactants (e.g. an acid dissolved among liquids).
- a heterogeneous catalyst is in a different state (e.g. solid iron speeding up the gases in the Haber process; a car's catalytic converter).
Practice
A heterogeneous catalyst is one that is:
Heterogeneous = different state (e.g. solid catalyst, gas reactants); homogeneous = same state.
Practice
Solid iron speeding up the gas reaction in the Haber process is an example of a:
The solid iron is in a different state from the gaseous reactants, so it is a heterogeneous catalyst.
You've got it
Key idea
- a catalyst speeds up a reaction, is not used up, and gives a route with lower $E_A$
- lower $E_A$ → more molecules can react → faster rate; $\Delta H$ is unchanged
- homogeneous = same state as reactants; heterogeneous = different state (e.g. solid iron, catalytic converter)