Difference Between Boiling Point and Evaporation

Thekey differencebetween boiling point and evaporation is that蒸发发生在液体表面，而沸点是温度vaporizationtakes place from the liquid mass.

从液体中蒸发到产生蒸气的蒸发可以通过两种方式发生。一种方法是在沸点产生蒸气。在另一种方法中，蒸发发生在沸点以下。我们将其称为蒸发。尽管这两个过程在蒸气状态下产生分子，但产生它们的方式是不同的。

内容

1.Overview and Key Difference
2.What is Boiling Point
3.What is Evaporation
4.并排比较 - 沸点与表格蒸发
5.概括

What is Boiling Point?

Simply, the boiling point means the temperature at which a liquid or a solvent will start to boil. We can define it for a fixed pressure; normally theatmospheric pressure。In other words, it is the temperature at which a liquid starts to vaporize. Therefore, at this temperature, thevapor pressureequals to the atmospheric pressure.

In the first place, boiling points of substances are affected by many factors. As external factors, the atmospheric temperature affects it. For example, a liquid in a vacuum has a lower boiling point than it is in the normal atmospheric pressure. Similarly, a liquid in a high pressure will have a relatively higher boiling point.

决定因素

此外，液体本身的化学和物理特性也会影响沸点。例如，如果液体中分子的分子量较高，则与具有较低分子加权化合物的液体相比，沸点将具有更高的沸点。化学键也影响沸点。与相应的烷烃相比，酒精将具有更高的沸点。在这里，原因是酒精分子之间存在氢键。烷烃don’t have strong hydrogen bonds; rather, they will have weakVan der Waals interactions。因此,打破stro所需要的能量ng bonds is larger in alcohols, which increases the boiling point of it.

Figure 01: Boiling Point of Water

Apart from that, the boiling points are useful for separation of each substance from a mixture. The technique that we use for this purpose is distillation. It is the fundamental behind the petroleum distillation as well. There, petroleum contains a large number of hydrocarbons with differing number of carbons. Some are straight chains, some branched, and some are aromatic. Therefore, the boiling points of these differ from each other. However, it is hard to isolate every molecule separately since their boiling points are varying with small amounts. However, it is possible to purify them to some degree. Hence, in petroleum distillation, we can separate molecules with closer molecular weights in a temperature range.

What is Evaporation?

Evaporation is the process of changing a liquid into its vapor stage. We use the word “evaporation” specifically when the vaporization happens from the surface of the liquid. Liquid vaporization can also happen at the boiling point where evaporation happens from the whole liquid mass. But then, we do not call it evaporation.

Difference Between Boiling Point and Evaporation

Figure 02: Evaporation is a Surface Process

Furthermore, evaporation can be influenced by various factors such as the concentration of other substances in the air, surface area, pressure, the temperature of the substance, density, flow rate of air, etc.

What is the Difference Between Boiling Point and Evaporation?

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into vapor. Whereas, evaporation is the process of changing a liquid into its vapor stage. Hence, the key difference between boiling point and evaporation is that evaporation takes place on the surface of the liquid whereas, at boiling point, vaporization takes place from the whole liquid mass. Here, evaporation of a particular liquid takes place below the boiling point.

此外，在沸点，液体形成气泡，蒸发中没有气泡形成。因此，这是沸点和蒸发之间可观察到的差异。此外，在沸点，为分子提供热量，并将能量用于形成蒸气。但是在蒸发中，不提供外部热量。相反，分子相互碰撞时会产生能量，并且该能量用于逃避蒸气状态。因此，这是沸点和蒸发之间的显着差异。

Below is an infographic on the difference between boiling point and evaporation that tabulates all these differences.

摘要 - 沸点与蒸发

沸点是当我们为液体提供外部热能时发生蒸发的温度。但是，蒸发是一个自发的过程，我们不提供任何外部能量。总而言之，沸点和蒸发之间的关键区别在于蒸发发生在液体表面，而沸点是从整个液体质量中发生蒸发的温度。

Reference:

1. Helmenstine，Anne Marie博士“化学沸点的定义。”ThinkCo，2018年12月24日。Available here
2. Libretexts. “12.4: Evaporation and Condensation.” Chemistry LibreTexts, National Science Foundation, 26 Nov. 2018.Available here