Calculate the enthalpy change per mole of the substance dissolved for the following:
A calorimeter contains 28 g of water at 12 degree Celsius. When 2 g of a substance with molar mass 56 is added, it dissolves and the temperature of the solution increases to 27 degree Celsius
The enthalpy change when the substance is dissolved is reflected in the heat released when that is done. The heat released raises the tempereature of the water.
Here, 2 gram of a substance with a molar mass of 56 is dissolved in 28 g of water. The result is an increase in the temperature of water from 12 degree Celsius to 27 degree Celsius.
2 gram of the substance is equal to 2/56 moles. The heat capacity of water is 4.1855 [J/(g·K)]. To raise the temperature of 28 g of water from 12 degree Celsius to 27 degree Celsius requires (27 - 12)*28*4.2 = 1764 J
For 1/28 mole of the substance the enthalpy change is 1764 J. For 1 mole it is 1764*28 = 49392 J
The enthalpy change per mole when the substance is dissolved is 49.392 kJ/mol