Catalyst Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Catalyst.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

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

A helper that makes the reaction easier but isn't used up in the process.

Read the full concept explanation β†’

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Catalyst starts by naming reactants and products, then checks conservation with a balanced equation.

Common stuck point: Students often know a formula related to catalyst but skip the recognition step: Am I tracking reactants, products, atom conservation, evidence of new substances, and the balanced equation? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I tracking reactants, products, atom conservation, evidence of new substances, and the balanced equation?

Worked Examples

Example 1

easy
In the decomposition of hydrogen peroxide, MnO2\text{MnO}_2 acts as a catalyst: 2H2O2β†’MnO22H2O+O22\text{H}_2\text{O}_2 \xrightarrow{\text{MnO}_2} 2\text{H}_2\text{O} + \text{O}_2. Explain the role of MnO2\text{MnO}_2.

Answer

MnO2Β lowersΒ EaΒ andΒ isΒ notΒ consumed\text{MnO}_2\text{ lowers } E_a\text{ and is not consumed}

First step

1
MnO2\text{MnO}_2 provides an alternative pathway with lower activation energy for the decomposition.

Full solution

  1. 2
    It speeds up the reaction but is not consumed β€” it can be recovered unchanged after the reaction.
  2. 3
    Without the catalyst, H2O2\text{H}_2\text{O}_2 decomposes very slowly at room temperature.
Catalysts are essential in both industrial chemistry and biology (where they are called enzymes). They increase reaction rates without altering the products or the equilibrium position.

Example 2

medium
Explain the difference between a homogeneous catalyst and a heterogeneous catalyst. Give one example of each.

Example 3

medium
A reaction has Ea=80E_a = 80 kJ. With a catalyst, Eaβ€²=60E_a' = 60 kJ. At 300 K, by what factor does the rate increase? (Use k∝eβˆ’Ea/RTk \propto e^{-E_a/RT}, R=8.314Β J/(mol\cdotpK)R = 8.314\ \text{J/(molΒ·K)}.)

Example 4

medium
Sketch (describe) the reaction profile of an exothermic reaction with and without a catalyst, labeling EaE_a, Eaβ€²E_a', Ξ”H\Delta H.

Example 5

hard
A reaction's rate doubles when a catalyst lowers EaE_a at constant TT. Approximately how much was EaE_a lowered? (RT=2.5RT = 2.5 kJ/mol.)

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
Enzymes are biological catalysts. Does an enzyme change the Ξ”H\Delta H of a biochemical reaction?

Example 2

medium
A catalyst is added to a reaction and the reaction finishes faster. What changes, and what does not change about the reaction?

Example 3

easy
What is a catalyst?

Example 4

easy
How does a catalyst speed up a reaction?

Example 5

easy
Is a catalyst consumed in the overall reaction?

Example 6

easy
Does a catalyst appear in the net balanced equation?

Example 7

easy
Does a catalyst change the Ξ”H\Delta H of a reaction?

Example 8

easy
Does a catalyst shift the position of equilibrium?

Example 9

easy
In 2H2O2β†’MnO22H2O+O22H_2O_2 \xrightarrow{MnO_2} 2H_2O + O_2, what role does MnO2MnO_2 play?

Example 10

easy
What are biological catalysts called?

Example 11

medium
A reaction's EaE_a drops from 75 kJ to 45 kJ when a catalyst is added. By how much did the catalyst lower EaE_a, and did Ξ”H\Delta H change?

Example 12

medium
A substance speeds up a reaction and is fully recovered afterward. Is it a reactant or catalyst? Justify.

Example 13

medium
Why does a catalyst reach equilibrium faster without changing the yield?

Example 14

medium
An industrial process uses iron as a catalyst for ammonia synthesis. Why is the iron not listed as a reactant?

Example 15

medium
A catalyst participates in intermediate steps. How can it still be 'not consumed'?

Example 16

medium
Compare the effect of a catalyst on rate versus its effect on the amount of product at equilibrium.

Example 17

medium
A catalyst becomes coated and stops working ('poisoned'). Was it consumed by the reaction it catalyzed?

Example 18

medium
Why does adding a catalyst not help a reaction that is already at equilibrium produce more product?

Example 19

medium
A catalyzed reaction reaches the same yield 5 times faster. Explain why faster does not mean more product.

Example 20

challenge
In 2SO2+O2β‡Œ2SO32SO_2 + O_2 \rightleftharpoons 2SO_3 with a V2O5V_2O_5 catalyst, explain what the catalyst does and does not change about this equilibrium.

Example 21

challenge
A student claims that because a catalyst appears in the mechanism, it must be either a reactant or a product. Refute this.

Example 22

challenge
Two reactions have Ea=90E_a = 90 kJ. Reaction P uses a catalyst dropping EaE_a to 50 kJ; reaction Q is heated. Both speed up. Explain the different reasons.

Example 23

easy
Does a catalyst change the rate of the forward reaction, the reverse reaction, or both?

Example 24

easy
Platinum in a catalytic converter speeds up the oxidation of CO without being used up. What kind of substance is platinum here?

Example 25

easy
Which of these does a catalyst change: rate, Ξ”H\Delta H, equilibrium position, EaE_a?

Example 26

easy
At the end of a catalyzed reaction, how does the mass of catalyst compare to the start?

Example 27

medium
Enzymes are described as 'specific.' What does this mean compared with industrial inorganic catalysts?

Example 28

medium
A catalyst lowers EaE_a from 100 kJ to 75 kJ. The reaction has Ξ”H=βˆ’40\Delta H = -40 kJ. What is EaE_a for the reverse reaction with the catalyst present?

Example 29

medium
A flask of H2O2H_2O_2 sits for hours with little change. A pinch of MnO2\text{MnO}_2 is added and gas vigorously evolves. Why?

Example 30

medium
In the Contact process, V2O5V_2O_5 catalyzes 2SO2+O2β‡Œ2SO32\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3. Is V2O5V_2O_5 written in the balanced equation?

Example 31

medium
A homogeneous catalyst is in the ____ phase as the reactants, while a heterogeneous catalyst is in a ____ phase.

Example 32

medium
Lead in old gasoline poisoned platinum catalytic converters. What does 'poisoning' mean here?

Example 33

medium
Why is a powdered catalyst usually more effective than the same mass in a single lump?

Example 34

hard
Acid catalyzes the hydrolysis of an ester. After the reaction, the H+\text{H}^+ concentration is unchanged. Why is acid considered a catalyst here even though H+H^+ appears in the mechanism?

Example 35

hard
Two reactions A and B both reach the same equilibrium yield. A uses a catalyst; B does not. Which costs less industrial energy and why?

Example 36

hard
For N2+3H2β‡Œ2NH3\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3 (Ξ”H<0\Delta H < 0), explain why a catalyst alone does not raise yield, but adjusting TT and PP can.

Example 37

hard
Iodide ion catalyzes peroxide decomposition: H2O2+Iβˆ’β†’H2O+IOβˆ’H_2O_2 + I^- \to H_2O + IO^- then H2O2+IOβˆ’β†’H2O+O2+Iβˆ’H_2O_2 + IO^- \to H_2O + O_2 + I^-. What is the catalyst, and what is the net equation?

Example 38

hard
An enzyme works best at 37 Β°C. At 80 Β°C it stops working even though kinetic theory predicts a higher rate. Why?

Example 39

hard
Chlorofluorocarbons (CFCs) catalyze ozone destruction: Cl+O3→ClO+O2Cl + O_3 \to ClO + O_2 then ClO+O→Cl+O2ClO + O \to Cl + O_2. What two features mark Cl as a catalyst?

Example 40

challenge
A student claims a catalyst could be used to convert graphite into diamond at room temperature. Why is this false?

Example 41

challenge
In autocatalysis, a product of the reaction catalyzes the reaction. Sketch how the rate vs time graph differs from a normal reaction.
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Background Knowledge

These ideas may be useful before you work through the harder examples.

activation energy