Definition
Catalyst is a substance that increases rate of reaction by providing an alternative pathway with a lower activation energy for the reaction to proceed. It remains chemically unchanged at the end of reaction #ChemistryDefinitions
Characteristics of Catalysts
- Provides alternative pathway which has a lower activation energy for the reaction to proceed.
- original pathway with a higher activation energy is still available
- Catalysts only changes speed (increases reaction rate), but does not affect yield of chemical reaction.
- final amt of products formed after reaction remains same/
- only affects time taken to form final amt of product
- Only small amount of catalyst needed to change rate of reaction
- Remains chemically unchanged at the end of the reaction, but physical appearance might change.
- same amt of catalysts present at beginning and end of reaction
- possible for catalyst to undergo chemical changes at an intermediate stage of reaction → but will be reformed at end of reaction
- They are selective → only catalyse certain reactions
- Impurities can poison/inactivate them. then they cannot catalyse reactions
Catalysts are often transition metals or their compounds
| Reactions | Catalyst | Note |
|---|---|---|
| Haber process - reaction of hydrogen with nitrogen to produce ammonia (link to ammonia) | finely divided iron | iron is a transition metal |
| reactions that take place in catalytic converter (link to chap 22 - Maintaining air quality) | platinum or rhodium or palladium | these elements are transition metals |
| decomposition of hydrogen peroxide | magnesium(IV)oxide | manganese is a transition metal. manganese(IV)oxide is a compound of transition metal |
| conversion of vegetable oil to margarine | nickel | nickel is a transition metal |
| examples of non transition metal catalysts |
- Yeast - in prod of ethanol from glucose solution
- Concentrated sulfuric acid in esterification
- aluminium oxide and silicon dioxide in cracking of hydrocarbons (petroleum)
How Does Catalyst increase ROR
Industrial Catalysts
Biological Catalysts
Sample
Explain why presence of finely divided iron increases ROR between nitrogen and hydrogen gas to produce ammonia gas
- finely divided iron is a catalyst which provides an alternative pathway with a lower activation energy for the reaction to proceed
- more reacting particles (of nitrogen and hydrogen gas or and molecules) now have energy equal to or greater than the activation energy.
- Thus frequency of effective collisions between reacting particles (of nitrogen and hydrogen gas or and molecules) increases and the rate of reaction also increases
some laundry detergents have enzymes added to break down oil/other stains → that would otherwise require high heat or strong chemicals to remove. enzymes operate at optimally milder temp → stubborn stains can be removed using these detergents with warm water.
remain CHEMICALLY UNCHANGED