Define the sublimation of an organic compound



As sublimation, seldom too sublimation, one describes in thermodynamics the process of the immediate transition of a substance from the solid to the gaseous aggregate state. Under the pressure and temperature conditions under which sublimation occurs, there is no liquid aggregate state, as can be seen in the phase diagram on the right. These conditions are also known as sublimation pressure (physics) and sublimation temperature, or taken together as Sublimation point. This in turn is part of the sublimation curve of the phase diagram, which is given in the adjacent example by the phase boundary line between solid and gas below the triple point.

The phase change in the opposite direction to sublimation is called resublimation, whereby the resublimation point for pure substances is identical to the sublimation point. In the case of mixtures, it must be noted that both can differ and therefore the direction of the phase transition also plays a role in this case.

If there is a sublimation temperature at normal pressure, this is called the normal sublimation temperature and the substance is tabulated with its value without additionally specifying the sublimation pressure.

Every substance absorbs the so-called sublimation heat during its sublimation, which is equal to the sum of the heat of fusion and evaporation.

Examples

  • Dry ice, frozen carbon dioxide at -78.5 ° C, sublimes when exposed to heat and therefore immediately turns into a gas. Under normal pressure, no liquid such as B. with water ice, which is why the name dry ice came about.
  • Boron, carbon, iodine and arsenic, but also organic compounds such as camphor, change into a gaseous state like carbon dioxide when heated under normal pressure.
  • When processing materials using lasers, sublimation occurs in some processes with high pulse power. The material does not burn, but changes directly from the solid to the gaseous state. The result is a very clean cut with no slag or frayed edges.

Category: Thermodynamic Process