Final answer:
Dry ice sublimes by transitioning directly from a solid to a gas at -78.5°C (-109°F) without passing through the liquid state, due to its finite equilibrium vapor pressure. This process is visible when 'smoke' forms as it is placed in a warmer environment.
Step-by-step explanation:
In order for dry ice to sublime, there must be a change of state from solid straight to gas. This process occurs at -78.5°C (-109°F), where solid carbon dioxide (CO₂), also known as dry ice, sublimes directly into carbon dioxide gas. Conditions like room temperature and standard pressure facilitate this transition. The equilibrium vapor pressure of dry ice is not zero, allowing sublimation to occur. A common visualization of sublimation is the formation of "smoke" when dry ice is placed in a warmer environment, such as a liquid, which leads to the cooling of the liquid and generation of dense mist. The opposite process, where gas turns directly into a solid without passing through the liquid phase, is known as deposition, an example of which would be the formation of frost.