Catalysts · ⁨催化剂⁩

A shortcut for reactions

• A catalyst 催化剂 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.

How a catalyst works

• A catalyst provides a different reaction mechanism 反应机理 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.

A catalyst gives a route with lower activation energy; the enthalpy change is unchanged

Two types

• a homogeneous catalyst 均相催化剂 is in the same physical state as the reactants (e.g. an acid dissolved among liquids).
• a heterogeneous catalyst 多相催化剂 is in a different state (e.g. solid iron speeding up the gases in the Haber process; a car's catalytic converter).

A homogeneous catalyst mixes in with the reactants; a heterogeneous one is a separate surface

How a catalyst changes the picture

• A catalyst gives an alternative pathway with a lower activation energy.
• More molecules now have enough energy to react, so the rate rises — without being used up.

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