i m doing the kinetic of iodine and propanone in acid condition using colorimeter and observing the absorbance and initially i dont think i will need a calibration curve becos absorbance is poprptional to concentration and i only need to look the shape of the graph to determine the order of the reaction, hence i plot an graph with absrobance against time and find the Initial rate for each concentrations of the reactnats and plot a graph wiht rates agasint concentration. now the problem is i also wanna know the activation energy and need to plot the arrhenius plot lnk =lna-lnE/PT. now i wanna save time, so i use the absorbance against time graph to find the initial rate of the reaction and use the rate law ,rate=k[r]^e[g]^f,(at this point of the experiment i expected that i kno the order of the reaction alreayd) and basiclly find k and i just wanna ask, since absorbance is proportional to concentration , thus will the tangent at time zero at absorbance against time graph be the initial rate value for my experiment or is it missing a constant?? secondly is my method of determining activation energy experiment sound correct??