Sublimation process in thermodynamics

Sublimation is a physical process that happens when a solid goes straight from a solid state to a gaseous (vapor) state, without going through a liquid state firstștii.știiștii. At a certain temperature, the latent heat of sublimation is the amount of heat needed to turn a unit mass of solid into a unit mass of gas. For example, the latent heat of sublimation of ice at 0°C is estimated to be 2,838 kJ/kg. This is how much heat is needed for ice to turn into vapor. This process is the most important part of how ice and snow crystals grow in the air. This process is the opposite of the deposition process.

Process of sublimation

Sublimation is when something goes from being solid to being a gas without going through the liquid state first

Sublimation is an endothermic process that happens at temperatures and pressures below a substance’s triple point on its phase diagram, which is the lowest pressure at which the substance can exist as a liquid. Deposition or sublimation is the opposite of sublimation. This is when a substance goes straight from a gas to a solid. Sublimation has also been used as a general term for a change from solid to gas followed by a change from gas to solid (deposition). When a liquid turns into a gas, it does so through evaporation from the surface if it is below the boiling point of the liquid, and through boiling with the formation of bubbles in the interior of the liquid if it is at the boiling point. However, when a solid turns into a gas, it always does so through sublimation from the surface, and there is no difference between the two.

Most chemical compounds and elements have three different states at three different temperatures when they are at normal pressures. In these situations, there must be a liquid state in between the solid and gaseous states. The pressure being talked about is the partial pressure of the substance, not the total pressure of the whole system, like atmospheric pressure. So, all solids that have a significant amount of vapor pressure at a certain temperature (like water ice just below 0 °C) can usually melt in air. Some substances, like carbon and arsenic, are hard to get as liquids, so sublimation is much easier than evaporation from the melt.

The word “sublimation” means a change in physical state. It is not used to describe a chemical reaction that turns a solid into a gas. For instance, when solid ammonium chloride is heated, it breaks up into hydrogen chloride and ammonia. This is not sublimation; it is a chemical reaction. In the same way, burning candles made of paraffin wax to make carbon dioxide and water vapor is not sublimation, but a chemical reaction with oxygen.

Sublimation happens when heat is absorbed, which gives some molecules enough energy to overcome the forces of attraction between them and escape into the vapor phase. It is an endothermic change because the process needs more energy. You can figure out the enthalpy of sublimation, which is also known as the heat of sublimation, by adding the enthalpy of fusion and the enthalpy of vaporization.

Sublimation as a way to clean

Chemists use sublimation as a way to clean up compounds. A solid is usually put in a sublimation machine and heated while the machine is under a vacuum. Under this lower pressure, the solid evaporates and condenses as a pure compound on a cold surface (cold finger), leaving behind a non-volatile residue of impurities. Once the heating stops and the vacuum is taken away, the purified compound can be taken from the surface where it is cooling. A temperature gradient is used to make the purification process even more effective and to separate different fractions. Most systems use an empty glass tube that is slowly heated in a controlled way. Material flows from the hot end, where the first material is put, to the cold end, which is connected to a pump stand. By controlling temperatures along the length of the tube, the operator can control the zones of re-condensation. Very volatile compounds are pumped out of the system completely (or caught by a separate cold trap), moderately volatile compounds re-condense along the tube according to their different volatilities, and non-volatile compounds stay in the hot end. This kind of vacuum sublimation is also the best way to clean organic compounds for use in the organic electronics industry, where very high purity levels (often above 99.99%) are needed to meet the standards for consumer electronics and other uses.

Energy of sublimation

The enthalpy of sublimation, also called the heat of sublimation, is the amount of heat needed to turn one mole of a solid substance into a gas at a certain temperature and pressure, usually standard temperature and pressure (STP). It is the same as the energy that holds the solid together. It is also the same as the standard enthalpy of formation of gaseous metal atoms for metals that are made up of only atoms.  Most of the time, the heat of sublimation is measured in kJ/mol, but the less common kJ/kg is also used.

Conclusion

From the following article we can conclude that A substance’s enthalpy of sublimation, also known as the heat of sublimation, is the amount of heat necessary to transform one mole of a substance from a solid state to a gaseous state at a certain combination of temperature and pressure, which is typically standard temperature and pressure Its value is equal to the cohesive energy of the material at a given temperature.