I followed the degradation of dye till 24 hour .. so how I should calculate rate constant because i take UV with a gape of 1 hour. what its unit will be?
first order the rate constant is in inverse time. Usually sec-1, but can be min-1 or hr-1 for slow rate.
second order the rate constant is M-1 sec-1 (where M is molarity - moles/liter ) again it might make sense for slow rates to use minutes or hours but sec is the usual time unit for SI units.