2. (10 points) Ice packs utilize an and therefore cools the area the reaction, t

Question

2. (10 points) Ice packs utilize an and therefore cools the area the reaction, the ice pack gets "eracked which allows the chemieala ln w with which the ice k in in cact T compartments of the ice pack to mix. One example of an endeothermile teartn can occur in an ice pack involves solid barium hydrole octabyirai solid ammonium nitrate to form aqueous barium nitrate. water. The balanced reaction is resction tha extalydtste tini-with ammonia, snd li Ba(OH)2 8H,0()+2NH NO)Ba(NOsh(og)+2N)101,D The standard enthalpies of formation for the reactants and produrte in thie venrtivn are provided in the table below Compound NH NO:() NHs(g) H200) 365.6 Ba(NOs)a (aq) 952.4 45.9 -285.8 a. Calculate Hrxn for this reaction. b. An ice pack contains 0.125 g of barium hydroxide octabydrate a ammonium nitrate to react completely. If the ice pack is in contac 3.0 in area of skin, what temperature change is felt by the skin? of skin is 0.10 mm and the density of skin is 1.05 g/cm. The 259 8(oH2 3H,0 skin is 3.38 J/g. C

Explanation / Answer

a)

HRxn = Hproducts - Hreactants

HRxn = (Ba(NO32 + 2NH3 + 10 H2O) - (Ba(OH)2*8H2O + 2NH4NO3)

Hrxn = (-952.4 + 2*-45.9 + 10*-285.8) - (-3342.2 + 2*-365.6)

HRXn = 171.2 kJ/mol

b)

m = 0.125 g of barium hydrate

MW of Ba(OH)2 * 8H2O = MW of Ba(OH)2 + 8 * MW of H2O = 171.34 + 18*18 = 495.34 g/mol

mol = mass/MW = 0.125 /495.34 = 0.00025235

1 mol =  171.2 kJ

0.00025235 mol = 0.00025235*171.2 = 0.0432 kJ

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