A calorimeter contains 34.0 mL of water at 14.0 C . When 2.50 g of X (a substanc

Question

A calorimeter contains 34.0 mL of water at 14.0 C . When 2.50 g of X (a substance with a molar mass of 60.0 g/mol ) is added, it dissolves via the reaction X(s)+H2O(l)X(aq) and the temperature of the solution increases to 27.5 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 = 34*1 = 34 grams

mass of x = 2.5 grams

mass o f solution = 36.5 grams

specific heat of water = 4.18 j/g.c

DT =27.5-14 = 13.5 c

q released = 36.5*4.18*13.5 = 2059.7 joule

       No of mol of X = 2.5/60 = 0.0417 mol

q = -DH

DH = -2059.7/0.0417 = -49.4 Kj/mol

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