Define sublimation.

Asked by vk1994 | 14th Jul, 2008, 04:31: PM

Expert Answer:

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Sublimation of an element or compound is a transition from the solid to gas phase with no intermediate liquid stage. Sublimation is a phase transition that occurs at temperatures and pressures below the triple point.

At normal pressures, most chemical compounds and elements possess three different states at different temperatures. In these cases the transition from the solid to the gaseous state requires an intermediate liquid state. However, for some elements or substances at some pressures the material may pass directly from a solid into the gaseous state. This can occur if the atmospheric pressure exerted on the substance is too low to stop the molecules from escaping from the solid state.

The opposite of sublimation is deposition. The formation of frost is an example of meteorological depositionCarbon dioxide is a common example of a chemical compound that sublimes at atmospheric pressure—a block of solid CO2 (dry ice) at room temperature and at atmospheric pressure will turn into gas without becoming a liquid. Iodine is another example of a substance that produces fumes on gentle heating. In contrast to CO2, though, it is possible to obtain liquid iodine at atmospheric pressure by controlling the temperature at just above the iodine's melting point. Snow and other water ices also sublime, although more slowly, at below-freezing temperatures. This phenomenon, used in freeze drying, allows wet cloth to be hung outdoors in freezing weather and retrieved later in a dry state . Naphthalene, a common ingredient in mothballs, also sublimes easily. Arsenic can also sublime at high temperatures. Sublimation requires additional energy and is an endothermic change

Answered by  | 14th Jul, 2008, 07:13: PM

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