A 0.75 g sample of NaCl is added to 35.0 gH2O in a Styrofoam cup and stirred unt
ID: 975455 • Letter: A
Question
A 0.75 g sample of NaCl is added to 35.0 gH2O in a Styrofoam cup and stirred until it dissolves. The temperature of the solution drops from 24.8 to 24.5 C.
What is the heat of solution of NaCl expressed in kilojoules per mole of NaCl?
Express your answer using two significant figures.
A 0.75 g sample of NaCl is added to 35.0 gH2O in a Styrofoam cup and stirred until it dissolves. The temperature of the solution drops from 24.8 to 24.5 C.
What is the heat of solution of NaCl expressed in kilojoules per mole of NaCl?
Express your answer using two significant figures.
H = ? kJmolExplanation / Answer
m = mass of solute + mass of solvent = 0.75 g + 35.0 g = 35.75 g
cg = specific heat capacity of water = 4.18 JoC-1g-1
T = change in temperature = |Tfinal - Tinitial|
= |24.5 – 24.8| = 0.3oC
q = m x cg x T
= 35.75 x 4.18 x 0.3 = 44.83 J
Molar mass of NaCl = 22.99 + 35.45 = 58.44 g / mol
n = Moles of NaCl = 0.75 / 58.44 = 0.0128
Since tempereature of solution decreases, the reaction is endothermic and Hsoln will be positive.
Hsoln = q / n = 44.83 / 0.0128 = 3502.34 J / mol = 3.5 kJ / mol
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