Difference Between Sublimation and Evaporation

Main Difference – Sublimation vs Evaporation

Sublimation and evaporation are terms used to describe phase transitions of matter. The phase of matter is the form of matter where the properties of matter are uniform everywhere. The three main phases of matter are solid phase, liquid phase, and gaseous phase. A phase transition is converting the phase of matter from one phase to another. Sublimation is the transition of matter from a solid phase to gaseous phase. Evaporation is the transition of matter from liquid phase to gaseous phase. This is the main difference between sublimation and evaporation.

Key Areas Covered

1. What is Sublimation
      – Definition, Mechanism, Examples
2. What is Evaporation
      – Definition, Mechanism, Examples
3. What are the Similarities Between Sublimation and Evaporation
      – Outline of Common Features
4. What is the Difference Between Sublimation and Evaporation
      – Comparison of Key Differences

Key Terms: Evaporation, Gaseous Phase, Liquid Phase, Matter, Phase, Phase Transition, Solid Phase, Sublimation, Triple Point

What is Sublimation

Sublimation is the transition of solid phase into gaseous phase. During this phase transition, the matter does not go through a liquid phase. The solid directly turns into a gas. This reaction is an endothermic reaction since chemical bonds between molecules should be broken down in order to release them to air. Since energy is released when chemical bonds form energy should be given in order to break them. Therefore, it is endothermic. This energy is calculated as the enthalpy of sublimation.

Sublimation occurs at temperatures and pressures below the triple point of a substance. The triple point of a substance is the temperature and pressure in which the substance exists in all three phases (solid phase, liquid phase, and gaseous phase). Below the triple point, solid water sublimates, changing directly into a gas with a temperature increase, and never passing through the liquid phase.

Main Difference - Sublimation vs Evaporation

Figure 1: Dry Ice Sublimation

Examples for sublimation include dry ice turning into gaseous carbon dioxide at room temperature and pressure. Naphthalene is an organic compound that sublimes easily at standard temperature and pressure.

What is Evaporation

Evaporation is the transition of liquid phase into gaseous phase. This is an endothermic process. The intermolecular forces between molecules in liquid should be broken down in order to form its vapor. This reaction requires energy. Therefore, it is an endothermic reaction. This is the opposite reaction of condensation. Evaporation is directly related to the temperature. When the temperature is increased, the rate of evaporation is also increased.

Difference Between Sublimation and Evaporation

Figure 2: Water Evaporation from the Surface

Evaporation of a liquid occurs on the surface of the liquid. The molecules near the surface of the liquid have a low amount of intermolecular forces compared to the molecules in the middle or bottom of the liquid. Therefore the molecules in the surface can be released easily. These molecules are the first to be converted into the gaseous phase.

There are several factors that affect the rate of evaporation. Some of these factors are given below.

The concentration of the substance in air – if there is a high concentration of the evaporating substance in air, then the evaporation occurs slowly.
The flow rate of air – a higher flow rate increases the evaporation.
Intermolecular forces – if the intermolecular forces are stronger, then the enthalpy of evaporation is high. Then the evaporation is slow.
Surface area – a large surface area is helpful for higher evaporation.

Similarities Between Sublimation and Evaporation

Both sublimation and evaporation produce a gas at the end.
Both are endothermic
In both processes, intermolecular forces are broken down in order to release the molecules.

Definition

Sublimation: Sublimation is the transition of solid phase into gaseous phase.

Evaporation: Evaporation is the transition of liquid phase into gaseous phase.

Initial Phase

Sublimation: The initial phase for sublimation is a solid phase.

Evaporation: The initial phase for evaporation is a liquid phase.

Enthalpy

Sublimation: The enthalpy of sublimation gives the amount of energy that is required for sublimation to occur.

Evaporation: The enthalpy of evaporation gives the amount of energy that is required for evaporation to occur.

Conclusion

Sublimation and evaporation are terms used to name phase transitions of matter. Although both these processes describe the conversion of matter into the gaseous phase, the terms are different from each other. The main difference between sublimation and evaporation is that sublimation is the phase transition from solid to gas whereas evaporation is the phase transition from liquid to gas.

References:

1.“Evaporation.” Wikipedia, Wikimedia Foundation, 4 Oct. 2017, Available here.
2.“What is Sublimation in Chemistry? – Definition, Process & Examples.” Study.com, Available here.

Image Courtesy:

1. “Dry Ice Sublimation 2” By Christopher from Salem, OR, USA – Fun with Dry Ice 2Uploaded by Diaa_abdelmoneim (CC BY-SA 2.0) via Commons Wikimedia
2. “Vaporization” by Tristan Schmurr (CC BY 2.0) via Flickr