Part A Instant cold packs, often used to ice athletic injuries on the field, con
ID: 1041940 • Letter: P
Question
Part A 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: Calculate the change in enthalpy for the reaction in kilojoules per mole. (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 and include the appropriate units. In order to measure the enthalpy change for this reaction, 1.25 g of NH4NOs 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. ? ,xn = 1 Value UnitsExplanation / Answer
mass of NH4NO3 = 1.25 g
moles of NH4NO3 = 1.25 / 80.04 = 0.0156 mol
mass of solution = 25 g
temperature drop = 25.8 - 21.9 = 3.9 oC
Q = m Cp dT
= 25 x 4.18 x - 3.9
Q = - 407.55 J
delta H = - Q / n
= 407.55 x 10^-3 / 0.0156
delta H = 26 kJ/mol