A calorimeter contains 18.0 mL of water at 11.0 C . When 1.50 g of X (a substanc
ID: 692247 • Letter: A
Question
A calorimeter contains 18.0 mL of water at 11.0 C . When 1.50 g of X (a substance with a molar mass of 62.0 g/mol ) is added, it dissolves via the reaction X(s)+ H 2 O(l)X(aq) and the temperature of the solution increases to 29.5 C . Calculate the enthalpy change, H , for this reaction per mole of X . Assume that the specific heat of the resulting solution is equal to that of water [4.18 J/(g C) ], that density of water is 1.00 g/mL , and that no heat is lost to the calorimeter itself, nor to the surroundings.
Explanation / Answer
mass of water = volume x density
= 18.0 x 1
= 18 g
total mass of the solution = 18 + 1.50 = 19.50 g
moles of X = 1.50 / 62 = 0.0242
Q = m Cp dT
Q = 19.5 x 4.18 x (29.5 -11)
Q = 1508 J
Q = 1.508 kJ
H = - Q / n
= -1.508 / 0.0242
= -62.3 kJ / mol
H = - 62.3 kJ / mol
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