A well insulated calorimeter containing 100 ml of water was calibrated by dissolving a known amount of sodium chloride in the calorimeter. The dissolution of sodium chloride in water can be represented by the equation: NaCl(s) + aq Na*(aq) + Cl(aq) AH=+3.90 kJ mol-¹ The temperature of the calorimeter was initially 18.00 °C. A sample of 2.55 g of sodium chloride was dissolved in the 100 mL and the temperature was recorded as 16.30 °C. The calibration factor of the calorimeter is (express your answer to 2 decimal places) 0.42 kJ °C-1
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.
Mass of NaCl used m = 2.55 g
Molar mass of NaCl = 1 x Na + 1 x Cl = 1 x 22.99 + 1 x 35.45 g/mol = 22.99 + 35.45 = 58.44 g/mol
Number of moles of NaCl used is mass of NaCl/molar mass of NaCl = 2.55 g/58.44 g/mol = 0.0436 moles
Heat of a solution, H = +3.90 kJ/mol
Energy of solution, E = H x number of moles of NaCl = +3.90 kJ/mol x 0.0436 moles = 0.17004 kJ
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