The rate constant of a particular reaction can be determined by measuring the UV/Vis absorbance spectrum at specific time intervals. Using mercury dithizonate again as an example, one can shine light on the sample to turn the solution blue, then run a UV/Vis test every 10 seconds (variable) to see the levels of absorbed and reflected wavelengths change over time in accordance with the solution turning back to yellow from the excited blue energy state. From these measurements, the concentration of the two species can be calculated. The mercury dithizonate reaction from one conformation to another is first order and would have the integral first order rate law : lnt)=−kt+ln[A(initial). Therefore, graphing the natural log (ln) of the concentration versus time will graph a line with slope -k, or negative the rate constant. Different rate orders have different integrated rate laws depending on the mechanism of the reaction.