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In thermodynamics, the enthalpy of sublimation, or heat of sublimation, is the heat required to sublimate (change from solid to gas) one mole of a substance at a given combination of temperature and pressure, usually standard temperature and pressure (STP). It is equal to the cohesive energy of the solid.
The form of the cooled surface often is a so-called cold finger which for very low-temperature sublimation may actually be cryogenically cooled. If the operation is a batch process , then the sublimed material can be collected from the cooled surface once heating ceases and the vacuum is released.
Solid carbon dioxide sublimes rapidly along the solid-gas boundary (sublimation point) below the triple point (e.g., at the temperature of −78.5 °C, at atmospheric pressure), whereas its melting into liquid CO 2 can occur along the solid-liquid boundary (melting point) at pressures and temperatures above the triple point (i.e., 5.1 atm, − ...
Its construction and principle of operation is simple. It consists of a titanium filament through which a high current (typically around 40 A) is passed periodically. This current causes the filament to reach the sublimation temperature of titanium, and hence the surrounding chamber walls become coated with a thin film of clean titanium.
The density of dry ice increases with decreasing temperature and ranges between about 1.55 and 1.7 g/cm 3 (97 and 106 lb/cu ft) below 195 K (−78 °C; −109 °F). [3] The low temperature and direct sublimation to a gas makes dry ice an effective coolant, since it is colder than water ice and leaves no residue as it changes state. [4]
Graph of temperature of phases of water heated from −100 °C to 200 °C – the dashed line example shows that melting and heating 1 kg of ice at −50 °C to water at 40 °C needs 600 kJ The terms sensible heat and latent heat refer to energy transferred between a body and its surroundings, defined by the occurrence or non-occurrence of ...
In the following table, material data are given with a pressure of 611.7 Pa (equivalent to 0.006117 bar). Up to a temperature of 0.01 °C, the triple point of water, water normally exists as ice, except for supercooled water, for which one data point is tabulated here. At the triple point, ice can exist together with both liquid water and vapor.
A typical phase diagram.The solid green line applies to most substances; the dashed green line gives the anomalous behavior of water. In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium. [1]