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Solids, liquids, and gases can be found in the same isolated environment. One can easily place a rock, some, air, and some water in a closed box and still find them in their phases after 24 hours at a controlled temperature. However, if we enclose water vapor, water, and ice, in a container, after 24 hours at a controlled temperature, we expect to find either water, vapor, or ice in the whole container depending on the temperature that was set. Surprisingly enough, this isn’t true on every planet.
By changing planet, we change the atmospheric pressure influencing the container. This change in atmospheric pressure is due to a change in the quantity of atmospheric gases and the magnitude of gravity of that planet. A strange behavior could be witnessed if the container was moved to a certain planet and elevation to allow 0.006 atm. At exactly 0.01 degrees Celcius, all three phases would still be present after 24 hours.
If you read last week’s article, you may have watched a video about a recent discovery; a fourth phase of matter. Time crystals, the fourth phase, are a recent discovery, so we do not know much about their behavior. For this article, we will neglect this new phase and focus on the three other phases of matter; liquid, solid, and gas. Feel free to leave a comment if you know more about the application of the fourth phase relating to the triple point of a substance.
The triple point of a substance is the point at which the three phases of a substance can coexist. To have this strange property, specific pressure and temperature must be established in the environment of the substance. The triple point of water would be a specific pressure and temperature at which we would find vapor, ice, and water in equilibrium.
When phases coexist in equilibrium, they are present even after a long time has elapsed (so long as the conditions remain ideal). This means that the ice will not melt, but the water will not freeze either. The gas will not liquefy, but the water will not evaporate either. There are several points of equilibrium. To identify them, it is helpful to look at the graph below.
In this graph, a rough analysis of the phases of water has been sketched. As can be seen along the axes, the graph shows which phase will be present at a certain pressure and temperature. The lines separating the colored regions are also points of equilibrium. On those lines, both phases can be present in the given conditions. The triple point is the point at which the three phases connect, which also happens to be the point at which all three phases coexist in equilibrium. On Earth, there is roughly 1 atm. That is why water freezes/melts at 0 degrees and vaporizes/condenses at 100 degrees Celcius.
From the graph, you will also notice that there is a point labeled, critical point. Like the triple point, the critical point is quite complex. I have decided to write about it later in the month. In the meantime, feel free to research it on your own. Also, if any reader knows more about the fourth phase of matter and how it applies to these points, please leave a comment below.
Sources & Further Reading
This article from Britannica is full of facts and definitions that apply to this topic. For instance, if you didn’t know what a phase was, you can read more about it in the article. It also includes some helpful visuals.
Blogs are not always reliable, but in this case, the information is accurate. The author describes the triple point in different words and also includes a helpful video. If the chart from this article was too complicated, check out his simplified chart.
This video shows the behavior of water at the triple point. The water is both boiling and freezing meaning that all three phases are present. The freezing process generates ice, the boiling water generates water vapor, and the fact that there is water boiling means that the liquid is also present at that point. Plus, even after a long period of time, water would still be present since it would condense back into a liquid when touching the ice.
Video Description: “This experiment demonstrates the triple point of a substance. Watch how water behaves at the triple point where it co-exists in solid, liquid and vapour form. There is also a short description of where the triple point lies on a P-T-diagram.” It was created by mechanical engineering students and the Centre for New Media at Bergen University College, Norway.
This website talks more about the triple point of substances. It includes a chart with the triple points of several other substances. What is unique about this website is that it talks in Pascals and several other units rather than just Celcius and atm.
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