Instant cold packs used to ice athletic injuries on the field contain ammonium nitrate and water separated by a thin plastic divider. When the divider is broken, the ammonium nitrate dissolves according to the endothermic reaction: NH4NO3(s) ® NH4+(aq) + NO3- (aq) In order to measure the enthalpy change for this reaction, 1.25 g of ammonium nitrate is dissolved in enough water to make 25.0 mL of solution. The initial temperature is 25.8 oC, and the final temperature (after the solid dissolves) is 21.9 oC. Calculate the change in enthalpy for the reaction in kJ per mole of NH4NO3. (Use 1.00 g/mL as the density of the solution and 4.18 J/(g oC) as the specific heat capacity.)
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.
- Instant cold packs used to ice athletic injuries on the field contain ammonium nitrate and water separated by a thin plastic divider. When the divider is broken, the ammonium nitrate dissolves according to the endothermic reaction:
NH4NO3(s) ® NH4+(aq) + NO3- (aq)
In order to measure the enthalpy change for this reaction, 1.25 g of ammonium nitrate is dissolved in enough water to make 25.0 mL of solution. The initial temperature is 25.8 oC, and the final temperature (after the solid dissolves) is 21.9 oC.
Calculate the change in enthalpy for the reaction in kJ per mole of NH4NO3. (Use 1.00 g/mL as the density of the solution and 4.18 J/(g oC) as the specific heat capacity.)
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