A student conducted an experiment in a Styrofoam cup calorimeter that contained 100.0 g of water at 25°C. The temperature was recorded over 2 minutes before adding 6.00 g of urea, H2NC(O)NH2(s) to the water. The temperature was recorded for another three minutes, after adding urea, with a final temperature of 21.8°C. a. Determine the change in temperature of the solution that results from the dissolution of the urea. b. According to the data, is the dissolution of urea in water an endothermic process or an exothermic process? Explain. c. Calculate the enthalpy change for the dissolution of the urea in kJ/mol. Assume that the specific heat capacity of the calorimeter is negligible and that the specific heat capacity of the solution of urea and water is 4.2 J g−1 °C−1 throughout the experiment. d. Calculate ∆H°reaction using standard enthalpies of formation. e. Compare your theoretical and experimental value
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.
1. A student conducted an experiment in a Styrofoam cup calorimeter that contained 100.0 g of water at
25°C. The temperature was recorded over 2 minutes before adding 6.00 g of urea, H2NC(O)NH2(s) to
the water. The temperature was recorded for another three minutes, after adding urea, with a final
temperature of 21.8°C.
a. Determine the change in temperature of the solution that results from the dissolution of the urea.
b. According to the data, is the dissolution of urea in water an endothermic process or an exothermic
process? Explain.
c. Calculate the enthalpy change for the dissolution of the urea in kJ/mol. Assume that the specific heat
capacity of the calorimeter is negligible and that the specific heat capacity of the solution of urea and
water is 4.2 J g−1 °C−1 throughout the experiment.
d. Calculate ∆H°reaction using standard enthalpies of formation.
e. Compare your theoretical and experimental value
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