KS3 · Chemistry

What catalysts do

A potato, a car exhaust and the making of fertiliser look nothing alike, but the same trick is working in all three. Rebuild the loop below and you'll spot it.

Rebuild the loop

What does an enzyme do, and why can it do it again?

2 stages are missing. Use the rest of the loop to work out which goes where.

  1. Stage 1: Substrate binds

    The substrate (the molecule that is about to react) fits into the enzyme's active site. Think lock and key: the enzyme is the lock, the active site is the keyhole and the substrate is the key. Only the correctly shaped key fits.

  3. Stage 3: Products are released

    The new substances made in the reaction, the products, are let go.

…and stage 4 leads back to stage 1.

Which idea is yours?

What is a catalyst, really?

Four students are arguing about catalysts. Each one sounds very sure of themselves.

Which of these is closest to what you think right now?
How sure are you?

Predict, then check

Same volume of hydrogen peroxide in each test tube. Only the substance you add changes.

You add iron oxide to one tube, copper oxide to another and manganese dioxide to the third. Which one gives lots of oxygen bubbles, quickly?

Catalytic converter

?

Reason it through

Why is a catalytic converter fitted to the exhaust of a petrol or diesel car?

Link 1 of 4

First link · your turn

First, what comes out of the engine that is a problem?

2
Locked — reveal the link above first
3
Locked — reveal the link above first
4
Locked — reveal the link above first

Same family?

Enzymes and the other catalysts

Enzymes are catalysts too. Tick the group (or both groups) each item belongs to, then check how you did.

  • A Enzymes (biological catalysts)
  • B Catalysts used in industry and vehicles
  1. Speeds up a reaction
  2. Is not used up in the reaction
  3. Is specific to particular reactions
  4. Can be reused
  5. Is made of protein
  6. Has an active site
  7. Amylase: starch → smaller sugars
  8. Protease: proteins → amino acids
  9. Catalase: hydrogen peroxide → water + oxygen
  10. Iron in the Haber process: nitrogen + hydrogen ⇌ ammonia
  11. Platinum or rhodium in a catalytic converter

Write it in your own words

The potato investigation

You have: potato, a cork borer, hydrogen peroxide and washing-up liquid. The class compared three conditions: cold, room temperature and hot.

A class investigated catalase using potato and hydrogen peroxide. Write a short description of what they could do and what they would see, then say which condition you think catalase worked best in. [5 marks]

0 words · your answer stays on this page and is not sent anywhere.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

The helper that speeds a reaction up, then walks away unchanged

What you need to know

  • A catalyst speeds up a chemical reaction without itself being used up or chemically changed, and it is not one of the reactants.
  • The reaction still takes place without the catalyst, just much more slowly.
  • Catalysts are specific to particular reactions: different reactions require different catalysts.
  • An enzyme is a biological catalyst made of protein. The substrate binds to its active site, the reaction is catalysed there, the products are released and the enzyme is reused.
  • Catalysts make processes more efficient and more cost effective, and they can be reused.

The big picture

A catalyst speeds up a particular reaction without being used up or chemically changed. Enzymes are biological catalysts: the substrate binds to the active site, the products are released and the enzyme is reused. The same idea cleans up car exhausts and helps make ammonia for fertilisers.

Key points

1A catalyst speeds up a reaction, isn't used up and isn't a reactant.
2Manganese dioxide is a good catalyst for the breakdown of hydrogen peroxide into water and oxygen. Iron oxide and copper oxide are not.
3Catalytic converters use transition metals such as platinum or rhodium to turn toxic exhaust gases into less harmful ones.
4The Haber process uses an iron catalyst to make ammonia from nitrogen and hydrogen, and ammonia is used to make many fertilisers.
5Enzymes are specific because only a substrate of the correct shape fits the active site, like the right key in a lock.
6Amylase breaks starch into smaller sugar molecules, protease breaks proteins into amino acids, and catalase speeds up the decomposition of hydrogen peroxide.

Worked example

Problem

Here is the word equation for making ammonia: nitrogen + hydrogen ⇌ ammonia. The process uses an iron catalyst. A friend says, "Iron must be a reactant, because it's in the process." Is your friend right?

⚠ Watch out

Writing that a catalyst speeds up every reaction. Catalysts are specific to particular reactions. For example, manganese dioxide was a good catalyst for the breakdown of hydrogen peroxide, but iron oxide and copper oxide were not.

🧠

Memory hook

Speeds it up, not used up. A catalyst is like a key that fits only its own lock, and the lock can be used again and again.

✓

Check yourself

Without looking back: in the enzyme loop, which stage shows the enzyme is not used up? And what happens if a substrate has the wrong shape for the active site?

Flashcards

(15)
What is a catalyst?
A chemical that speeds up the rate of a chemical reaction without itself being used up or chemically changed.
Is a catalyst a reactant? What happens if you leave it out?
No, a catalyst is not one of the reactants. The reaction still takes place without it, but much more slowly.
What does it mean that catalysts are specific?
Each catalyst works for particular reactions: different reactions require different catalysts.
Which of iron oxide, copper oxide and manganese dioxide was the best catalyst for hydrogen peroxide?
Manganese dioxide made lots of oxygen quickly. Iron oxide and copper oxide were not good catalysts for this reaction.
What does hydrogen peroxide break down into?
Water and oxygen. The oxygen can be seen as bubbles.
Why are catalysts so useful?
They make processes more efficient by speeding up reactions, they make them more cost effective, and they can be reused.
Which toxic gases come from petrol and diesel engines, and how do they form?
Carbon monoxide and carbon particulates come from incomplete combustion of the fuel. Nitrogen oxides form because high temperatures make nitrogen in the air react with oxygen.
What is a catalytic converter?
A catalyst made from transition metals such as platinum or rhodium, fitted to the exhaust system to speed up reactions that produce less harmful gases.
What does the Haber process make, and which catalyst does it use?
It makes ammonia (used to make many fertilisers) from nitrogen and hydrogen, using an iron catalyst.
What is an enzyme?
A biological catalyst, made of protein, that speeds up reactions in living cells. Enzymes are not used up in the reaction.
What are the substrate and the active site?
The substrate is the reactant molecule (or molecules). The active site is the part of the enzyme where the chemical reaction takes place.
Put the enzyme reaction in order.
The substrate binds to the active site, the reaction is catalysed there, the products are released, and the enzyme is reused.
In the lock-and-key model, what do the lock, the keyhole and the key stand for?
The lock is the enzyme, the keyhole is the active site and the key is the substrate. Only the correctly shaped key fits.
What do amylase and protease do?
Amylase speeds up the breakdown of large starch molecules into smaller sugar molecules. Protease enzymes break down proteins into amino acids.
What is catalase, and where is it found?
An enzyme found in nearly all living things exposed to oxygen, including potatoes. It speeds up the decomposition of hydrogen peroxide, which could harm living cells, into water and oxygen.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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