... is plotted. (The value of ln[y(t+?t)-yt] refer to Appendix 3) Graph 3 From the equation, y= -0.0276x - 4.9105 Slope of graph = -kobs = -0.0276 ? kobs = 0.0276 s-1 R/R? Method (Ratios of Rates) With pure first-order decays, the successive ratio must remain constant Where rm is the mean value of the successive ratios Rt/Rt+? along the whole kinetic curve. R = dy/dt As ? = 20 Table below is R in Successive 20 s interval Rate Time / s Absorbance (y) dy/dt Rt / Rt+? 0 0 0.2969208 -0.0084229 2.021965096 20 20 0.1556702 -0.0041657 1.784331363 40 40 0.08308411 -0.0023346 1.719107825 60 60 0.04393005 -0.00135803 1.869568315 80 80 0.02578735 -0.0007019 1.483869604 100 100 0.01699829 -0.00047302 1.785741035 120 120 0.0131073 -0.00021362 1.399960679 140 140 0.01098633 -0.00015259 1.25002048 160 160 0.008926392 -0.000137329 -------- Average of the Rt / Rt+? (rm) = 1.66432055 kobs = 0.025s-1 Discussions: Mercury dithizonates were used in this experiment. Metal dithizonates have several interesting properties including photoactivation by light of wavelength greater than 350nm, reversible colour changes, photochemical forward and fast thermal return reactions, and log term stability to visible and near ultraviolet light. The colour change accompanies the photoactivation of a cis-trans isomerization within the ligand as shown below. The orange form of mercury dithizoate is photosensitive because it is ...

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