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 ammonium divider is broken, the nitrate dissolves according to the following endothermic reaction: NHANO3 (8) NH4+ (ag) NO3 (ag) In order to measure the enthalpy change for this reaction, 1.25 goff NH4NO3 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 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. °C as the specific heat capacity.) Express your answer to two significant figures kJ/mol AH, Submit My Answers Give Up

Explanation / Answer

Here enthalpy change ?H = m.s.(T2-T1)

s = specific heat capacity = 4.18 J/g.oC

m = mass of solution = (25.0 mL) X (1.0g/mL) = 25.0 g

T2 = final temperature = 21.9oC

T1 = initial temperature = 25.8oC

By putting these values in the above equation we get,

?H = 25.0 g (4.18 J/g.oC).(3.9oC) = 407.55 J

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