When dry ice (solid carbon dioxide, CO2) sublimates into CO2 gas, the heat is absorbed from the surroundings. Sublimation is an endothermic process, meaning it requires the input of heat energy to break the intermolecular forces holding the solid together and convert it directly into a gas without passing through the liquid phase.
During the sublimation process, the heat is typically obtained from the surrounding environment. The dry ice absorbs heat energy from the surroundings, causing the solid CO2 molecules to gain enough thermal energy to break their bonds and transition into the gaseous phase. As a result, the temperature of the surroundings may decrease as the heat is transferred to the dry ice.
Conversely, when CO2 gas is cooled to turn it back into dry ice (a process known as deposition), the heat is released to the surroundings. Deposition is an exothermic process, meaning it releases heat energy as the gas molecules lose thermal energy and re-form into a solid.
During deposition, the heat energy that was absorbed during sublimation is released back into the surroundings. As the temperature of the CO2 gas decreases, the gas molecules lose thermal energy, and the intermolecular forces become strong enough to allow them to reassemble into a solid. The released heat is transferred to the surrounding environment, causing a temperature increase in the vicinity.
In summary, during the sublimation of dry ice into CO2 gas, heat is absorbed from the surroundings, and during the deposition of CO2 gas back into dry ice, heat is released to the surroundings. These processes involve the exchange of thermal energy with the surrounding environment.