Intermediate Topic 500 of 1102 Kinetics & Equilibrium
Inhibitors and Poisons
Substances that slow reactions or deactivate catalysts by blocking active sites.
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In-depth explanation of Inhibitors and Poisons
Inhibitors are substances that slow a reaction by binding to an intermediate or to the active site of a catalyst. Catalyst poisons are substances that adsorb strongly, and often irreversibly, onto the surface of a catalyst, permanently blocking its active sites and destroying its activity. Some inhibitors are deliberately added to foods and fuels to slow unwanted oxidation, as antioxidants do by intercepting radical chain carriers. Protecting catalysts from poisons is a major concern in industry, where feedstocks are purified to remove sulfur, lead or arsenic compounds before reaction. The distinction between an inhibitor and a poison is partly one of degree and mechanism.
Going deeper: Inhibitors and Poisons
Key ideas: Poisoning is distinguished from reversible inhibition by its persistence: even trace amounts, such as parts per million of sulfur, reduce activity because they occupy sites strongly. Fixes include guard beds, high temperature regeneration or controlled oxidation of coke. In biology cyanide binds cytochrome oxidase iron and carbon monoxide binds haemoglobin, acting as poisons of biological catalysts or carriers.
Common mistakes and connections: Students think an inhibitor reduces the equilibrium yield or is the same as a negative catalyst that raises Ea of the reverse step only. Inhibitors act by slowing a step in the mechanism, for instance by scavenging chain carriers. Another mistake is to treat poisoning as permanent in every case. Links to enzyme inhibition, catalytic converters and radical chain reactions.
Visualization of Inhibitors and Poisons
A poisoned catalyst has fewer active sites, so the maximum rate (Vmax) drops even though binding (Km) stays about the same. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Sulfur compounds in a feedstock poison nickel catalysts used in hydrogenation, so the feed must be desulfurized first.
Frequently asked questions about Inhibitors and Poisons
What is Inhibitors and Poisons?
Substances that slow reactions or deactivate catalysts by blocking active sites.
Is Inhibitors and Poisons a beginner, intermediate or advanced topic?
Inhibitors and Poisons is a intermediate topic in Kinetics & Equilibrium. It builds on the vocabulary of beginner topics in this area.
What should I learn before Inhibitors and Poisons?
Study these earlier topics in Kinetics & Equilibrium first: Clock Reactions, Rate vs Time Graphs, Catalytic Converters.
What comes after Inhibitors and Poisons?
The next topics in Kinetics & Equilibrium are Surface Catalysis Steps and Zeolites.
Can I practise Inhibitors and Poisons with quizzes?
Yes. The interactive lesson includes a self-check question on Inhibitors and Poisons, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Where Inhibitors and Poisons fits in Kinetics & Equilibrium
Inhibitors and Poisons is topic 81 of 91 in Kinetics & Equilibrium.