Instant cold packs, often 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 following endothermic reaction:
NH4NO3 (s) → NH4+ (aq) + NO3- (aq)
In order to measure the enthalpy change for this reaction, 1.25 g of NH4NO3 is dissolved in enough water to make 25.0 ml of solution. The initial temperature is 25.8 ○C and the final temperature (after the solid dissolves) is 21.9 ○C. Calculate the change in enthalpy for the reaction in kJ. (Use 1.0 g/ml as the density of the solution and 4.184 J/g ○C as the specific heat capacity.)
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