How Catalysts Affect Activation Energy

By lowering the energy of the activated complex (transition state), catalysts reduce the energy barrier.

3. They improve molecular orientation

Catalysts bring reactants into better alignment, increasing effective collision frequency.

The combination of these effects results in a lower activation energy and a higher reaction rate.

Energy Profile Diagrams With and Without a Catalyst

In an energy diagram:

• The uncatalyzed pathway shows a high activation energy peak.
• The catalyzed pathway shows a lower peak.
• The overall enthalpy change (ΔH) remains unchanged.

This diagram visually demonstrates why catalysts increase the rate without altering the final energy difference between reactants and products.

Biological Catalysts: Enzymes

Enzymes are natural catalysts found in living organisms.
They:

• Bind to substrates at active sites
• Lower activation energy dramatically
• Work under mild temperatures and pH conditions
• Are highly specific to particular reactions

Enzymes illustrate how powerful catalytic effects can be, enabling life’s essential biochemical processes.

Importance of Catalysts in Industry

Catalysts are essential for:

• Haber process (NH₃ production)
• Contact process (H₂SO₄ production)
• Polymer production
• Hydrocarbon cracking
• Environmental catalysis (catalytic converters)

Without catalysts, these processes would require extreme temperatures or pressures, making them inefficient or economically unfeasible.

Why Catalysts Don’t Affect Equilibrium Position

A common misconception is that catalysts shift equilibrium.
They do not.

Catalysts speed up both forward and reverse reactions equally, helping equilibrium reach its position faster but not changing that position.
Equilibrium depends on ΔG, ΔH, and temperature—not on activation energy.

FAQs

Does lowering activation energy always make a reaction faster?

Yes. With lower activation energy, more particles meet the required threshold for reaction, so the reaction rate increases.

Can a catalyst make a reaction spontaneous?

No. Catalysts do not change ΔH or ΔG. They make reactions faster but cannot make non-spontaneous reactions occur on their own.

Do catalysts always stay unchanged?

Catalysts are not consumed, but they can become poisoned or deactivated, especially in industrial environments.

Conclusion

Catalysts lower the activation energy of a reaction by offering an alternative pathway, stabilizing transition states, and improving molecular orientation. This significantly increases the reaction rate without changing the overall enthalpy or equilibrium position. Understanding this mechanism is essential for success in IB Chemistry and for applying kinetic principles in both laboratory and industrial settings.

Learn why the mole allows chemists to connect atomic-scale particles to measurable quantities used in real experiments.