How to Calculate Heat of Sublimation
- 1). Set up your calorimeter according to its usage instructions.
- 2). Calculate the temperature change, deltaT, of the water by subtracting the final water temperature from the initial water temperature. Thus, if the temperature of the water in the calorimeter dropped from 55.0 degrees Celsius to 22.6 degrees Celsius, then deltaT = 22.6 - 55.0 = -32.4 degrees Celsius.
- 3). Calculate the heat lost by the water, Q, according to the equation Q = m * c * deltaT, where m represents the mass of water and c represents water's specific heat capacity, or 4.184 joules per gram degree Celsius.
Note that 1 milliliter of water weighs about 1 gram. Therefore, if the calorimeter was filled with 200 mL of water, which would weigh 200 g, then Q = 200 * -32.4 * 4.184 = -27,100 joules of heat. The negative sign in front of the value indicates that the heat was lost by the water. The heat gained by the sublimed substance will be equal in quantity but opposite in sign to the heat lost by the water. - 4). Calculate the heat of sublimation of the substance by dividing the heat absorbed by the substance, as calculated in step 2, by the mass of substance in grams. For example, if 47.5 g of substance was placed in the calorimeter, then the heat of sublimation would be 27,100 / 47.5 = 571 J/g.
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