A 1.50 ml sample of KCl is added to 35.0 ml H_2O in a Styrofoam cup and stirred
ID: 1073242 • Letter: A
Question
A 1.50 ml sample of KCl is added to 35.0 ml H_2O in a Styrofoam cup and stirred until dissolved. The temperature of the solution drops from 24.8 to 22.4 degree C. Assume that the specific heat and density of the resulting solution are equal to those of water, 4.18 J/(g C) and 1.00 g/mL, respectively and assume that no heat is lost to the calorimeter itself, nor to the surroundings. Is the reaction endothermic or exothermic (circle the correct answer)? What is the heat of solution of KCl expressed in kilojoules per mole of KCl?Explanation / Answer
heat absorbed(q) = msDT
m = mass of solution = 35+1.5 = 36.5 g
s = specificheat of solution = 4.184 j/g.c
DT = 24.8 - 22.4 = 2.4 c
q = 36.5*4.184*2.4 = 0.366 kj
as the temperature decreases , it is endothermic
mass of KCl dissolved = d*v
= 1*1.5 = 1.5 g
no of mole of KCl = w/mwt = 1.5/74.55 = 0.02 mole
DHsolution = +q/n = 0.366/0.02 = +18.3 kj/mol
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