Part A A calorimeter contains 35.0 mL of water at 15.0 C . When 2.00 g of X (a s

Question

Part A A calorimeter contains 35.0 mL of water at 15.0 C . When 2.00 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 29.5 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.

Explanation / Answer

mass of water = 35.0 x 1.00 = 35.0g

temperature rise = 29.5 - 15 = 14.5 oC

specific heat of water = 4.18 J / goC

Q = m Cp dT

   = 35 x 4.18 x 14.5

= 2121.35 J

moles of X = 2 / 58 = 0.0345

H = - Q / n = - 2121.35 x 10^-3 / 0.0345

H = - 61.5 kJ/mol

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