[hopzz]

if im determining the Ea of the catalyzed and uncatalyzed iodination of propanone, can i not use a colorimeter? can i simply measure the time taken for the colour change to happen?

[Borek]

This is about as vague as possible, more details on the experiment please.

Broadly speaking it can be, or can be not possible, depending on the setup. But the best approach is to not wait till "the color changes", but to measure the color change, as it will allow to follow the reaction progress in a quantitative way.

[Corribus]

Agreed, very vague, but I will also point out that catalyzed reactions (e.g., those based on enzymes) often display non-Arrhenius behavior. So, extracting an activation energy from an Arrhenius plot may not be simple.