A calorimeter contains 142 g of water at 22.5 degree C. A 12-g sample of NaCl is

Question

A calorimeter contains 142 g of water at 22.5 degree C. A 12-g sample of NaCl is added to the water in the calorimeter. After the solid has dissolved, the temperature of the water is 21.4 degree C. Calculate the enthalpy of this discussion reaction in kJ/mol of NaCl. Assume that no heat is lost to the calorimeter and that the specific heat capacity of the solution is the same as that of pure water (Cs=4.18 J/g K). Which statement is TRUE? For a given reaction, q and delta_rH can always be used interchangebly.

Explanation / Answer

Mass of mixtute= mass of water+ mass of NaCl =142+12= 154 gms

specific heat of mixture = 4.18 j/g,deg.c

drop in temperature due to addition of NaCl= 22.5-21.4=1.1 deg.c

Change in enthalpy = mass*specific heat* temperature difference= 154*4.18*1.1=708 joules =0.708 Kj

moles of NaCl in 12 gm = mass/Molecular weiight= 12/58.5=0.205

Change in enthalpy/mole of NaCl= 0.708/0.205=3.453 Kj/mole( D is the correct answer)

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