A calorimeter contains 33.0 mL of water at 12.0 C . When 2.20 g of X (a substanc

Question

A calorimeter contains 33.0 mL of water at 12.0 C . When 2.20 g of X (a substance with a molar mass of 69.0 g/mol ) is added, it dissolves via the reaction X(s)+H2O(l)X(aq) and the temperature of the solution increases to 25.5 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/(gC)], that density of water is 1.00 g/mL, and that no heat is lost to the calorimeter itself, nor to the surroundings. Express the change in enthalpy in kilojoules per mole to three significant figures.

Explanation / Answer

Water volume= 33ml, mass of water= 33ml*(1g/ml)= 33 gm. mass of X= 2.2 gm

total mass =33+2.2 =35.2 gms

Heat added= mass* specific heat* temperature difference= 35.2*4.18*(25.5-12) =1986.336 Joules

moles of X= mass/Molecular weight= 2.2/69=0.032

Heat added/mole= 1986.336/0.032 Joules/mole=62298.72 Joules/mole =62.298 Kj/mole

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