A student was asked to determine the enthalpy of solution of KCIO3 in water using Styrofoam calorimetry. Calibration was performed by mixing 8.00 mL 0.050 M HCl with 2.00 mL 0.200 M NaOH. The neutralization reaction (AH = -55.85 kJ/mol) was accompanied by a temperature change from 25.0 to 28.3°C. Using the same calorimeter, 0.300 g KCIO3 (MW: 122.55) was dissolved in water and the temperature was observed to change from 23.6 to 17.3°C. (Assume that the total volume of the mixture in calibration is the same in the enthalpy measurement) What is the calorimeter constant in kJ/°C? What is the enthalpy of dissolution of KCIO3 in kJ/mol? Is the dissolution endothermic or exothermic? Explain.
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
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