How does a catalyst work?
2 marks · HardThe diagram below shows a reaction profile for an exothermic reaction. The activation energy for the uncatalysed reaction is much larger than for the catalysed reaction.
Describe what the dashed line on this diagram represents. Explain how a catalyst causes this change.
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Also accept: Dashed line shows alternative reaction pathway with lower activation energy provided by a catalyst; A catalyst provides an alternative route with lower activation energy, shown by the dashed line
Common mistakes: Stating that the catalyst lowers the activation energy without mentioning alternative route; Not linking diagram to catalyst's effect
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Marking points
B1 · 1 mark · Identifies dashed line as alternative pathway (or activation energy with catalyst) in reaction profile diagram
B2 · 1 mark · Explains that a catalyst provides an alternative reaction route with lower activation energy
Worked solution
The dashed line represents the alternative reaction pathway provided by a catalyst, which has a lower activation energy than the uncatalysed reaction.
A catalyst causes this change by giving the reaction an alternative route that requires less energy to get from reactants to products.