# When can colourimetry be used to determine the rate of reaction?

Can colourimetry be used if a coloured reactant react to give a coloured product? For example, in the reaction of reacting dichromate ions with oxalate ions in acidic environment, where dichormate ions (orange) react to give chromium three ions (green)?

• It can be used if reaction is slow enough. – Mithoron Jul 20 '18 at 23:44
• In a more general sense, spectroscopy is used nowadays to measure reactions on all time scales from tens of femtoseconds ($10^{-15}$ s) to hours. If a laser can be used to start the reaction these methods are now called 'pump-probe' but used to be called 'flash photolysis'. Rapidly mixing reactants that then react without using a laser to initiate it, which is the most general case, and using spectroscopy to monitor the colour change is called 'stopped flow' . – porphyrin Jul 22 '18 at 9:25