Question 16 Instant cold packs, often used to ice athletic injuries on the field

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Question 16 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: NHANO3 (s) NHM (aq) NO3 (ag) 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. Part A Calculate the change in enthalpy for the reaction. (Use 1.0 g/mL as the density of the solution and 4.18 J/g. as the specific heat capacity.) Express your answer to two significant figures AH, kJ/mol Submit My Answers Give U

Explanation / Answer

heat removed from water = 4.184 J/gC * 25.0g * (25.8 - 21.9)C = 407.94 J

no of moles of NH4NO3 = 1.25/80.043666 = 0.0156 mol

407.94/ 0.0156 = 26150 J/mol = 26.15 kj/mol

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