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INTRODUCTION Each chemical reaction involves an enthalpy change that leads to change in temperature. The amount of substance converted during the reaction determines the increase (i.e. exothermic reaction) or decrease (i.e. endothermic reaction) in temperature. INTRODUCTION (CONTD.) In thermometric titration, the reagent solution (titrant) is added to the sample at a constant rate until attaining the endpoint. The change in temperature of the reaction solution is plotted against the volume of titrant that is added. The titration endpoint can be identified by a break in the titration curve, and can be accurately determined by means of the second derivative. As the temperature sensor (Thermoprobe) has a 0.3 second response time and a 10-5K resolution, even minute changes in enthalpy can be monitored reliably. TITRATION (CONTD) Consider the titration reaction: aA + bB = pP Where: A = the titrant, and a = the corresponding number of moles reacting B = the analyte, and b = the corresponding number of moles reacting P = the product, and p = the corresponding number of moles produced TITRATION (CONTD) At completion, the reaction produces a molar heat of reaction ΔHr which is shown as a measurable temperature change ΔT. In an ideal system, where no losses or gains of heat due to environmental influences are involved, the progress of the reaction is observed as a constant increase or decrease of temperature depending respectively on whether ΔHr is negative (indicating an exothermic reaction) or positive (indicating an endothermic reaction). IDEALIZED TITRATION Figs. 1a & 1b. Idealized thermometric titration plots of exothermic (left) and endothermic (right) reactions
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