8.1.5Atomic Structure and the Periodic Table
Catalysts and Rate of Reactions
5 min read 4 parts Lesson 1 of 10 Unit quiz
Section 1 of 4What a Catalyst Does
A catalyst is a substance that changes the rate of a reaction without being used up.
Speeds up
- A catalyst increases the rate of a reaction and is chemically unchanged at the end of it.
Mass
- The mass of catalyst at the start and the end of a reaction is the same, so only small amounts are needed.
Equation
- A catalyst is not part of the balanced equation, but it can be written above or below the reaction arrow.
Equilibrium
- A catalyst speeds up the forward and reverse reactions equally, so it does not change the position of equilibrium or the yield.
Section 2 of 4Effect on the Rate
The effect of a catalyst is best understood through the activation energy.
1
A catalyst provides an alternative pathway for the reaction that has a lower activation energy.
2
More particles then have enough energy to react when they collide.
3
Successful collisions happen more often, so the rate of reaction rises.
4
The catalysed reaction reaches completion sooner but forms the same amount of product.
Section 3 of 4Catalysts in Industry
Catalysts are important in industry because they increase production without extra energy cost.
Catalysts in Industry
Haber process
- An iron catalyst is used at about 450 °C and 200 atm to speed up the reaction between nitrogen and hydrogen.
Contact process
- A vanadium(V) oxide catalyst speeds up the oxidation of sulfur dioxide to sulfur trioxide.
Cost
- Catalysts lower the energy requirements and increase production, which reduces the cost of manufacture.
Cracking
- Catalysts are used in cracking to break long-chain hydrocarbons into smaller, more useful molecules.
Section 4 of 4Exam Checklist & Tips
8.1.5 – Key Points for the Exam
- Catalyst A substance that speeds up a reaction and is chemically unchanged at the end.
- Alternative pathway A different route for a reaction with a lower activation energy.
- Activation energy The minimum energy needed for colliding particles to react.
- Catalysed reaction A reaction that proceeds faster because a catalyst is present.
Common Mistakes
- Saying a catalyst is used up during the reaction; it is recovered chemically unchanged.
- Writing that a catalyst increases the yield; it speeds up the rate but does not change the amount of product.
- Drawing the catalysed energy curve starting or finishing at a different level;
- it must start and finish at the same points as the uncatalysed curve.
- Stating that a catalyst lowers the energy of the products; it only lowers the activation energy.