How does a catalyst work?
3 marks · Easy| Description | Energy (kJ/mol) |
|---|---|
| Reactants | 120 |
| Peak without catalyst | 200 |
| Peak with catalyst | 140 |
| Products | 60 |
Calculate the activation energy without a catalyst.
What is the activation energy with a catalyst?
Describe how the catalyst affects the reaction profile diagram, using the values from the table.
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(a) 80 kJ/mol
(b) 20 kJ/mol
(c) The catalyst lowers the activation energy from 80 kJ/mol to 20 kJ/mol; on the diagram the peak is lower.
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Marking points
M1 (a) · 1 mark · Calculates activation energy without catalyst as 200 - 120 = 80 kJ/mol.
M1 (b) · 1 mark · Calculates activation energy with catalyst as 140 - 120 = 20 kJ/mol.
B1 (c) · 1 mark · Describes the catalyst lowers activation energy/peak from 80 to 20 kJ/mol. (follow-through)
Worked solution
(a) Activation energy without catalyst = Peak (no catalyst) - Reactants = 200 - 120 = 80 kJ/mol.
(b) Activation energy with catalyst = Peak (with catalyst) - Reactants = 140 - 120 = 20 kJ/mol.
(c) The catalyst lowers the activation energy shown by the lower peak (from 80 to 20 kJ/mol) on the diagram.