Experimentally, it is observed that the change in pressure exerted on a substance implies a change in melting and boiling temperature.
In these studies it is possible to observe:
1. Influence of Pressure on Fusion
Most substances, when receiving heat during the fusion process (transition from solid to liquid phase), have their volume increased. This is because when receiving heat, the degree of thermal agitation of the particles that make up the body increases, thus expanding its volume. However, some substances present the opposite behavior during the fusion process, when they receive heat to pass from the solid to the liquid phase, their volume is reduced. As substances that present this inverse behavior, water, iron bismuth and antimony can be highlighted.
It is verified that, when undergoing an increase in pressure, substances that have their volume increased in the fusion also have their fusion temperature increased; and those with reduced volume have a lower melting temperature.
Another characteristic of this inverse behavior of water is the increase in volume in solidification (passage of the phase liquid to solid), which explains the fact that a closed bottle filled with water ruptures when placed in the freezer.
2. Influence of Pressure on Boiling
In boiling (passage from the liquid to the gaseous phase), when receiving heat, the liquid has its volume increased. As for a certain pressure, each substance has its own boiling temperature (water boils at a pressure of 1 atm at a temperature of 100°C), when increasing the pressure on a liquid will cause an increase in its boiling temperature, so it becomes more difficult for the substance to pass from the liquid state to the gaseous.
This is used in pressure cookers, in which the vapors formed as a result of heating the water cannot escape from its interior and thus press on the surface of the water. As we saw above, an increase in pressure leads to an increase in the boiling temperature and in this way the water supports temperatures above 100°C, making food cook faster than in a pan ordinary.
By Nathan Augusto
Graduated in Physics
Source: Brazil School - https://brasilescola.uol.com.br/fisica/a-influencia-pressao-na-mudanca-fase.htm
