Instant cold packs used to treat athletic injuries contain solid NH4NO3 and a po

Question

Instant cold packs used to treat athletic injuries contain solid NH4NO3 and a pouch of water....what is the final temperature in a squeezed cold pack that contains 33.9 g of NH4NO3 dissolved in 138 g of water.

Instant cold packs used to treat athletic injuries contain solid NH4NO3 and a pouch of water. When the pack is squeezed, the pouch breaks and the solid dissolves, lowering the temperature because of the reaction HANOI (ag) AH r.An 25,700 J mol H,O endothermic (a) This reaction is o exothermic (b) What is the final temperature, in °C, in a squeezed cold pack that contains 33.9 g of NH4NO3 dissolved in 138 g of water? (Assume that the solution has the same specific heat as that of water, an initial temperature of 25.0 C, and no heat transfer between the cold pack and the environment. Hint: A solution is composed of a solute solvent. Number 43.86

Explanation / Answer

a)

since dHRxn is positive and it requires energy, this is ENDOthermic, meaning it will cool the surroundings

b)

Apply:

HRxn = 25700 J/mol

mol of NH4NO3 = mass/MW = 33.9/80.043 = 0.42352 mol of NH4NO3

so

total Q

Q = n*HRxn = 25700*0.42352 = 10884.464 J will be absorbed

so...

Qwater = -Qrxn

Qwater -10884.464 J

now

Qwater = m * C*(Tf-Ti)

substitute values, notet hat C = Specific heat of water 4.184 J

-10884.464 = 138 * 4.184 * (Tf-25)

Tf = -10884.464 / (138 * 4.184 ) + 25

Tf = 6.1489 °C

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