A calorimeter contains 19.0 mL of water at 14.0 ?C . When 1.80 g of X (a substan

Question

A calorimeter contains 19.0 mL of water at 14.0 ?C . When 1.80 g of X (a substance with a molar mass of 46.0 g/mol ) is added, it dissolves via the reaction X(s)+H2O(l)?X(aq) and the temperature of the solution increases to 26.0 ?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 = density*volume = 19.0*1.00 = 19 gram

moles of X = 1.80/46.0 = 0.03913 mol

dH for 0.03913 mol = mcdT = 19*4.18*(26-19) = 555.94 J

enthalpy change for per mole of X = 555.94 J/0.03913 mol = 14207.51 J/mol = 14.2075 kJ/mol

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