A calorimeter contains 16.0 mL of water at 14.5 C . When 2.50 g of X (a substanc

Question

A calorimeter contains 16.0 mL of water at 14.5 C . When 2.50 g of X (a substance with a molar mass of 58.0 g/mol ) is added, it dissolves via the reaction

X(s)+H2O(l)X(aq)

and the temperature of the solution increases to 25.0 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/(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

The enthaphy change for 2.5 gram = specific heat X mass of solution X T =

                                                      = 4.18 X (16+2.5) x (25-14.5) = 811.965 j

For 2.5 gram , the enthaphy change as 811.965 j

For 58 gram or 1 mole it will be = (58/2.5)X 811.965 =18837.588 j

                                                                                 = 18.837588KJ/Mol

H =

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