Problem: 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. (Use 1.0 g/mL as the density of the solution and 4.18 J/(g • ˚C) as the specific heat capacity.)

FREE Expert Solution

Step 1

q = mcTq = (1.25 g)(4.18 Jg·°C)(21.9°C - 25.8°C)

q = -20.3775 J


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Problem Details
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. (Use 1.0 g/mL as the density of the solution and 4.18 J/(g • ˚C) as the specific heat capacity.)

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