How does a catalyst work?
3 marks · NormalA reaction has reactants at an energy level of 95 kJ/mol, a peak (without a catalyst) at 155 kJ/mol, and products at 65 kJ/mol.
A catalyst provides an alternative pathway with a peak at 110 kJ/mol.
Calculate:
The activation energy without a catalyst.
The activation energy with a catalyst.
The difference in activation energy caused by the catalyst.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 60 kJ/mol
(b) 15 kJ/mol
(c) 45 kJ/mol
Common mistakes: Subtracting product from peak instead of reactant from peak; Forgetting the difference is always positive
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Marking points
M1 (a) · 1 mark · Correct subtraction: activation energy (without catalyst) = peak (without catalyst) - reactants (155 - 95).
A1 (b) · 1 mark · Correct subtraction: activation energy (with catalyst) = peak (with catalyst) - reactants (110 - 95).
A2 (c) · 1 mark · Difference in activation energy = answer to (a) - answer to (b) (allow follow through). (follow-through)
Worked solution
a) Activation energy without catalyst = peak (no catalyst) - reactants = 155 kJ/mol - 95 kJ/mol = 60 kJ/mol.
b) Activation energy with catalyst = peak (with catalyst) - reactants = 110 kJ/mol - 95 kJ/mol = 15 kJ/mol.
c) Difference = (activation energy without) - (activation energy with) = 60 kJ/mol - 15 kJ/mol = 45 kJ/mol.