A calorimeter contains 21.0 mL of water at 11.0\\, ^{\\circ}C. When 2.10 g of \
ID: 722745 • Letter: A
Question
A calorimeter contains 21.0 mL of water at 11.0, ^{circ}C. When 2.10 g of m X (a substance with a molar mass of 45.0 g/mol) is added, it dissolves via the reactionm X{(s)}+H_2O{(l)} ightarrow X{(aq)}
and the temperature of the solution increases to 25.5, ^{circ}C.
Calculate the enthalpy change, Delta H, for this reaction per mole of m X.
Assume that the specific heat and density of the resulting solution are equal to those of water [4.18 m J/(g cdot {^circ C}) and 1.00 m g/mL] and that no heat is lost to the calorimeter itself, nor to the surroundings.
Explanation / Answer
Heat = mCT
Q = (mass of H2O) x specific heat of H2O x (Tfinal-Tinitial)
Q = (21) x 4.18 x 14.5 = 1272.81 J
dH = delta H.
dH/g = Q/g = 1272.81/2.10 J/gm = 606.1 J/gm
dH/mol = Q/mol = (q/2.50)*molar mass = 606.1 x 45 J/mol = 27.27 kJ/mol
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