📘 IB Understanding
Catalysts increase the rate of reaction by providing an alternative reaction pathway with a lower activation energy (Eₐ). They are not consumed and do not appear in the overall equation.
How Catalysts Work
A catalyst speeds up a chemical reaction without being permanently changed. It does this by offering a completely different reaction mechanism that has a lower activation energy barrier. Because more particles now have sufficient energy to react, the rate increases.
Energy Profile: With and Without Catalyst
Key Points About Catalysts
| Feature | Effect |
|---|---|
| Activation energy | Lowered (provides alternative pathway) |
| Enthalpy change (ΔH) | Unchanged (same reactants and products) |
| Rate of reaction | Increased (both forward AND reverse) |
| Position of equilibrium | Unchanged (equilibrium is reached faster, but K stays the same) |
| Catalyst consumed? | No (regenerated at the end of the mechanism) |
Maxwell-Boltzmann Distribution
A catalyst does not change the shape of the Maxwell-Boltzmann curve or the average kinetic energy of particles. Instead, it shifts the activation energy threshold to the left, meaning a greater proportion of particles now have sufficient energy to react.
Maxwell-Boltzmann: Effect of a Catalyst
📋 Exam Note
Biological catalysts are called enzymes. The IB syllabus states that the different mechanisms of homogeneous and heterogeneous catalysts will not be assessed.
⚠️ Common Misconception
Catalysts do NOT "lower the activation energy" of the existing reaction. They provide a completely different pathway that happens to have a lower Eₐ. The original pathway still exists; the catalyst just offers a faster alternative route.
Think About It
If a catalyst increases the rate of both forward and reverse reactions equally, why does it not change the equilibrium position?
Because equilibrium is a ratio of forward and reverse rates. If both are increased by the same factor, the ratio stays the same. The system reaches equilibrium faster, but the final composition (and K) is unchanged.