Catalysts – Chemistry Lecture Review

A comprehensive set of flashcards covering definitions, mechanisms, industrial examples, benefits, and issues related to catalysts.

What is a catalyst?

A substance that increases the rate of a chemical reaction by providing an alternative pathway with a lower activation energy, without being chemically changed or used up.

How does a catalyst affect the activation energy (Ea)?

It lowers the activation energy, allowing more particles to have energy ≥ Ea and thus increasing the reaction rate.

Why does lowering Ea increase reaction rate?

A greater proportion of particles have sufficient energy for successful collisions, so more reactions occur per unit time.

How does a catalyst change a Boltzmann distribution diagram?

The overall curve shape stays the same, but the Ea line shifts left, enlarging the area under the curve beyond Ea.

Does a catalyst change the equilibrium position of a reversible reaction?

No. It speeds up both the forward and reverse reactions equally, reaching equilibrium faster but without altering the equilibrium yield.

Define a homogeneous catalyst.

A catalyst in the same phase (state) as the reactants, typically used in solution-phase reactions.

Give an example of a homogeneous catalyst.

H⁺ ions (acid) in esterification reactions.

Define a heterogeneous catalyst.

A catalyst in a different phase from the reactants, often a solid catalyst interacting with gaseous or liquid reactants.

Give an example of a heterogeneous catalyst.

Solid iron (Fe) used in the Haber process with gaseous N₂ and H₂.

List the three key steps in heterogeneous catalysis.

1) Adsorption of reactants on the catalyst surface, 2) Reaction with bond weakening/breaking, 3) Desorption of products.

What catalyst is used in the Haber process and for what reaction?

Iron (Fe) catalyzes N₂ + 3H₂ ⇌ 2NH₃.

What catalyst is used in the Contact process?

Vanadium(V) oxide, V₂O₅, catalyzing 2SO₂ + O₂ ⇌ 2SO₃.

What catalyst is used for hydrogenation of alkenes?

Nickel (Ni) for converting C₂H₄ + H₂ → C₂H₆.

Which metals are used in catalytic converters and what do they remove?

Platinum, palladium, or rhodium remove CO and NO, producing CO₂ and N₂.

What catalyst is used for hydration of ethene to ethanol?

Phosphoric acid, H₃PO₄, catalyzing C₂H₄ + H₂O → C₂H₅OH.

State three economic benefits of using catalysts in industry.

Lower energy costs, faster production rates, and improved atom economy (less waste).

State three environmental benefits of catalysts.

Reduced fossil fuel consumption, lower greenhouse gas emissions, and decreased release of harmful exhaust gases via catalytic converters.

What is catalyst poisoning?

Loss of catalyst activity when impurities strongly bind to active sites, blocking them and reducing effectiveness.

Give an example of catalyst poisoning in the Haber process.

Sulfur compounds can poison the iron catalyst.

Give an example of catalyst poisoning in automotive systems.

Lead in petrol poisoned catalytic converters (reason leaded fuel is largely banned).

How does a catalyst appear in a reaction mechanism?

It is introduced in an early step, participates in intermediate formation, and is regenerated in a later step; it can appear in the rate equation if rate-determining.

Summarize the key points about catalysts in one sentence.

Catalysts lower activation energy, speed reactions without being consumed, do not change equilibrium positions, can be homogeneous or heterogeneous, offer economic and environmental benefits, but are vulnerable to poisoning by impurities.