A calorimeter contains 33.0 mL of water at 15.0 C . When 2.10 g of X (a substanc

Question

A calorimeter contains 33.0 mL of water at 15.0 C . When 2.10 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 28.0 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

Explanation / Answer

dT = 28-15 = 13°C

Q = m*C*(dT)

Q = 33*4.18*13 = 1793.22 J

HRXN = -Q/n

n = mol = mass/MW = 2.10/46 = 0.04565 mol

HRXN = -1793.22 /0.04565 = -39281.92 J/mol = -39.28 kJ/mol

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