A calorimeter contains 18.0 mL of water at 15.0 degrees Celcius . When 1.80 g of

Question

A calorimeter contains 18.0 mL of water at 15.0 degrees Celcius . When 1.80 g of X (a substance with a molar mass of 42.0 g/mol) is added, it dissolves via the reaction X(s)+H2O(l)-->X(aq) and the temperature of the solution increases to 30.0 degrees Celcius . Calculate the enthalpy change, for this reaction per mole of X. Assume that the specific heat and density of the resulting solution are equal to those of water [4.18 J/g C and 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

Let UNITs guide you; always USE THEM in your calculation to prevent errors heat evoled = 4.184J/gC * (31+2.30)g * (25.5-15.0)C = ?? dH solution = - (heat evolved) / (2.30 g X / MW X g/mole) = ?? J/mole

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