Sublimation vs Deposition
Phase transition is changing the phases of a substance. This is affected by the external factors like temperature and pressure changes. For example, a liquid solidifies when the temperature is reduced to its freezing point, and it may go into the gas phase when the temperature is at its boiling point. Sublimation and deposition are also phase transitions, but they are a bit different than the normal.
What is Sublimation?
When a substance is in the solid phase, it can melt and come to the liquid phase. When further energy is given (in the form of heat) to this, it can evaporate and go into the gas phase. There are three main states as solid, liquid and gas and the transformation from one phase to another can take place. This process is known as the phase transition. Sometimes this may need heat, and sometimes heat is released during the process. Sublimation is a process like this but, normally, when phase is changed there is an order. Solid goes into the liquid phase and then to the gas phase; or if it is a gas, it should go through the liquid phase first and then to the solid phase. However, sublimation is different from this. It is the process of changing a solid substance into a gaseous substance without going through the liquid phase. In simple words, a solid substance directly evaporates and become a gas without being a liquid first. This process needs extra energy. Therefore, this is an endothermic process. By calculating the enthalpy of sublimation, the energy needed for this process can be found. This is calculated by adding both enthalpy of fusion and enthalpy of vaporization together. Sublimation occurs at temperatures and pressures below the triple point of the substance. For example, solid carbon dioxide sublimes at a very low temperature (-78.5°C) and at atmospheric pressure. Triple point of carbon dioxide is 5.2 atm and -56.4°C, and above this point, liquid carbon dioxide can also be obtained. Ice, iodine can also undergo sublimation. In sublimation, the chemical properties of the compound remains unaltered, but the physical properties may change. Moreover, there are some compounds which sublime because they are undergoing a chemical reaction. Sublimation is useful for various purposes. For example, it is used to purify chemical compounds.
What is Deposition?
The opposite process of sublimation is known as deposition. This is also known as de-sublimation. Here, a substance in the gas phase changes into a solid phase substance without passing the intermediate liquid state. This releases energy and, therefore, it is an exothermic process. This happens when forming ice or frost. In this process, water vapor directly goes into the solid phase (forming ice or frost). When this happens they remove thermal energy to the external environment.
What is the difference between Sublimation and Deposition?
• Sublimation is the opposite process of deposition.
• Sublimation is the process of changing a solid substance into a gaseous substance without going through the liquid phase. Deposition is the process of a substance in the gas phase changes into a solid phase substance without passing the intermediate liquid state.
• Sublimation is endothermic, and deposition is exothermic.