In this example, we find the enthalpy of solution from experimental data using a coffee-cup calorimeter. Our problem reads, "When 85.0 grams of lithium perchlorate is dissolved in 375.0 grams of water in a coffee-cup calorimeter, the temperature changes from 20.18 degrees Celsius to 31.21 degrees Celsius. Calculate the enthalpy of solution for lithium perchlorate in kilojoules per mole. Use C equals 4.18 joules per gram degree Celsius for the specific heat capacity of the solution." Our first step is to calculate the heat absorbed by the contents of the coffee-cup calorimeter. We can use the equation "heat equals mass times specific heat times the change in temperature." The total mass inside a coffee-cup calorimeter is 85.0 grams of lithium perchlorate plus 375.0 grams of water. Our change in temperature is the final temperature minus the initial temperature, which is 31.21 degrees Celsius minus 20.18 degrees Celsius. Completing the calculation, the contents of the coffee-cup calorimeter absorbed 21,208 joules to increase its temperature. Our next step is to calculate the thermal energy released by the dissolving process. We know the dissolving process releases thermal energy because when an ionic solid is dissolved in water and the temperature increases, the dissolving process is exothermic. The temperature is increasing because thermal energy is being released by the dissolving process, similar to a combustion reaction releasing thermal energy and increasing the temperature of the gas. So the energy released by the dissolving process has the opposite sign of the energy absorbed by the calorimeter's contents. Q solution should equal -21,208 joules. Our last step is to convert to kilojoules per mole of lithium perchlorate. We did not use one mole of lithium perchlorate in this experiment; we used 85.0 grams. So we'll start our dimensional analysis with the heat that was released, -21,208 joules, per 85.0 grams of lithium perchlorate. We can convert from joules to kilojoules using the definition of kilo. And we can use the molar mass of lithium perchlorate to convert from grams of lithium perchlorate to moles of lithium perchlorate. Completing the calculation, we get -26.5 kilojoules per mole of lithium perchlorate as the enthalpy of solution.