In the following experiment, solid CaCl2 (M = 110.98 g/mol) is dissolved in water: CaCl2(s) → Ca2+(aq) + 2Cl-(aq) ΔsolnH = ? kJ mol−1 A 4.00 g sample of CaCl2 is added to a coffee-cup calorimeter containing 125 g of H2O. The initial temperature of water in the calorimeter is 22.0°C and the final temperature is 27.5°C. What is the enthalpy change for the dissolution reaction (ΔsolnH) in kJ per mole of CaCl2? Assume the specific heat capacity of the solution is the same as water (Cs=4.18 J g-1 °C-1) and that no heat is lost to the calorimeter.
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.
In the following experiment, solid CaCl2 (M = 110.98 g/mol) is dissolved in water:
CaCl2(s) → Ca2+(aq) + 2Cl-(aq) ΔsolnH = ? kJ mol−1
A 4.00 g sample of CaCl2 is added to a coffee-cup calorimeter containing 125 g of H2O. The initial temperature of water in the calorimeter is 22.0°C and the final temperature is 27.5°C. What is the enthalpy change for the dissolution reaction (ΔsolnH) in kJ per mole of CaCl2?
Assume the specific heat capacity of the solution is the same as water (Cs=4.18 J g-1 °C-1) and that no heat is lost to the calorimeter.
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