Inhibitory Catalyst
Definition and meaning of Inhibitory Catalyst in chemistry.
An inhibitory catalyst, more commonly called a negative catalyst or simply an inhibitor, is a substance that decreases the rate of a chemical reaction, often by raising the effective activation energy or by interfering with a key intermediate in the reaction mechanism.
In more detail
Unlike a true catalyst, which speeds up the forward and reverse reactions equally by opening a lower-energy alternative pathway, an inhibitor typically works by consuming reactive intermediates (as radical scavengers do), poisoning a catalyst's active surface, or blocking an enzyme's active site. Because inhibition does not usually proceed through the same lowered-activation-energy mechanism that defines catalysis, IUPAC treats "negative catalyst" as an informal, somewhat misleading label and prefers the term "inhibitor." Like a genuine catalyst, however, an inhibitor does not change the equilibrium constant or the equilibrium position of a reversible reaction; it only slows how quickly that equilibrium is reached.
Key facts
| Field | Physical Chemistry |
|---|---|
| Also known as | Negative catalyst, inhibitor |
| Effect on equilibrium constant | None (affects rate only, not equilibrium) |
| Typical mechanisms | Radical scavenging, active-site blocking, catalyst poisoning |
Small amounts of hydroquinone are added to stored liquid acrylate or styrene monomers, where it scavenges free radicals and prevents the monomers from undergoing premature radical polymerization during shipping and storage.
Frequently asked questions
Is "negative catalyst" the officially correct scientific term?
Not really. IUPAC prefers "inhibitor" because inhibition usually does not work through the same lowered-activation-energy pathway that defines true catalysis; the substance often blocks or diverts the mechanism instead.
Can an inhibitor be consumed during the reaction, unlike a true catalyst?
Yes, often. Many inhibitors, such as radical scavengers, react with and are used up by reactive intermediates, whereas a true catalyst is regenerated unchanged at the end of the catalytic cycle.