2. Cold packs take advantage of the fact that dissolving NH4NO3 in water is an endothermic process. When 5.44 g of solid ammonium nitrate is added to 150.0 g of water in a coffee cup calorimeter, the temperature of the solution changes from 18.6 °C to a final temperature which you will determine. Calculate the enthalpy change for dissolving ammonium nitrate in water, in kJ/mol. Assume the specific heat of the solution is 4.2 J/g·K. final temp is 15.92 a. Write the dissolution reaction for NH4NO3(s). b. Since the dissolution of NH4NO3 is an endothermic process, do you expect the temperature to increase or decrease? How do you know? c. Calculate ∆rH usinig standard enthalpies of formation. d. Is the sign of ∆H consistent with the observation that the dissolution of NH4NO3 is endothermic? How do you know? e. Use ∆rH from part (c) to calculate qrxn (in Joules). f. Using the value of qrxn, determine the value of qsolution.
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.
2. Cold packs take advantage of the fact that dissolving NH4NO3 in water is an endothermic process. When
5.44 g of solid ammonium nitrate is added to 150.0 g of water in a coffee cup calorimeter, the temperature
of the solution changes from 18.6 °C to a final temperature which you will determine. Calculate the
enthalpy change for dissolving ammonium nitrate in water, in kJ/mol. Assume the specific heat of the
solution is 4.2 J/g·K. final temp is 15.92
a. Write the dissolution reaction for NH4NO3(s).
b. Since the dissolution of NH4NO3 is an endothermic process, do you expect the temperature to increase or
decrease? How do you know?
c. Calculate ∆rH usinig standard enthalpies of formation.
d. Is the sign of ∆H consistent with the observation that the dissolution of NH4NO3 is endothermic? How do
you know?
e. Use ∆rH from part (c) to calculate qrxn (in Joules).
f. Using the value of qrxn, determine the value of qsolution.
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Cold packs take advantage of the fact that dissolving NH4NO3 in water is an endothermic process. When 5.44
g of solid ammonium nitrate is added to 150.0 g of water in a coffee cup calorimeter, the temperature of the
solution changes from 18.6 °C to a final temperature which you will determine. Calculate the enthalpy
change for dissolving ammonium nitrate in water, in kJ/mol. Assume the specific heat of the solution is 4.2
J/g·K.
e. Use ∆rH from part (c) to calculate qrxn (in Joules).
f. Using the value of qrxn, determine the value of qsolution.
g. Using the value of qsolution, calculate ∆T, as well as the final temperature reached by the solution.
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