A calorimeter contains 17.0 mL of water at 15.0 C . When 1.50 g of X (a substanc

Question

A calorimeter contains 17.0 mL of water at 15.0 C . When 1.50 g of X (a substance with a molar mass of 51.0 g/mol ) is added, it dissolves via the reaction X(s)+H2O(l)X(aq) and the temperature of the solution increases to 27.0 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

17 mL of awater is the same as 17 g of water, let's calculate the heat:

Q = mCp(Tf-Ti)
Q = 17 * 4.184 * (27-15)
Q = 853.54 J

To get the enthalpy dH we need the moles so:
moles = 1.50 / 51 = 0.0294 moles

dH = 853.54 / 0.0294 = 29031.97 J/mol or 29.03 kJ/mol

Hope this helps

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