The saltsa NH,Br(s)NH(a)+Br(aq) following data: AH NH,Br(s)- 270.8 kJ mol AHENH(

Question

The saltsa NH,Br(s)NH(a)+Br(aq) following data: AH NH,Br(s)- 270.8 kJ mol AHENH(a)- -132.5 kJ mol AH? Br(aq)- -121.6 kJ mol (b Suppose 26.0 g of NH·Br is dissolved in 0.101 L of water at 229 C Calculate the temperature reached by the solution, assuming it to be an ideal solution with a heat capacity close to that of 101 g of pure water (specific heat-4.18Jg cl) oC (c) Heats of reaction find practical application in hot packs or cold packs. Would this dissolution reaction be appropriate for the preparation of a hot pack or a cold pack?

Explanation / Answer

Part a

Enthalpy change = sum of Enthalpy of formation of products - sum of Enthalpy of formation of reactants

H = Hf(NH4+) + Hf(Br-) - Hf(NH4Br)

= - 132.5 - 121.6 + 270.8

H = 16.7 kJ

Part b

H = - m x Cp x (T2-T1)

16.7*1000 J = - 127 g x 4.18 J/gC x (T2 - 22.9)C

22.9 - T2 = - 31.45

T2 = 8.55 °C

Part C

This is endothermic reaction

Cold pack

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