By Jack Brubaker, updated March 24, 2022
Sublimation is the direct transition of a solid into a gas, bypassing the liquid phase. Because the process absorbs energy, it is classified as endothermic. Scientists quantify the required energy and express it as the heat of sublimation, typically in joules per gram (J/g) or joules per mole (J/mol).
Follow the manufacturer’s instructions to assemble the calorimeter. Ensure that the container is sealed, the thermometer is properly positioned, and the sample is ready for introduction.
Record the initial temperature of the water and the final temperature after the sublimation event. Calculate the temperature change (ΔT) by subtracting the final value from the initial one. For example, if the water cools from 55.0 °C to 22.6 °C, ΔT = 22.6 °C – 55.0 °C = –32.4 °C.
Use the formula Q = m × c × ΔT, where m is the mass of the water (1 mL ≈ 1 g) and c is the specific heat capacity of water (4.184 J g⁻¹ °C⁻¹). With 200 mL of water, m = 200 g, ΔT = –32.4 °C, the heat loss is Q = 200 g × 4.184 J g⁻¹ °C⁻¹ × (–32.4 °C) = –27,100 J. The negative sign indicates heat loss; the sublimating substance gains an equal amount of heat.
Divide the magnitude of the heat absorbed by the sublimating material by its mass. If 47.5 g of the substance was used, the heat of sublimation is 27,100 J ÷ 47.5 g = 571 J g⁻¹.
