Water boils at 100 degrees Celsius because at this temperature, the atmospheric pressure is sufficient to allow water molecules to escape in the form of steam, which corresponds to the boiling point of water at standard atmospheric pressure.
The water molecule can be imagined like a little "Mickey Mouse": one oxygen atom in the center and two small hydrogen atoms attached to it. The oxygen pulls the electrons toward itself more, being a bit selfish at the edges, which gives water a polar molecular shape: the oxygen side is slightly negative and the hydrogen side is slightly positive. Thanks to these opposite charges, water molecules attract each other, forming sort of mini-magnets that stick together through what are called hydrogen bonds. These bonds are strong enough to create a tight network, but remain weak enough to be easily broken when you heat the water. When water reaches 100 degrees Celsius, the thermal agitation is sufficient to break these little hydrogen bonds, allowing the water molecules to escape as vapor.
The temperature at which water boils depends greatly on atmospheric pressure. At sea level, where the pressure is around one atmosphere, water actually boils at 100°C. If you go up in altitude, for example in the mountains, the atmospheric pressure decreases. Less pressure means that water molecules escape more easily, and thus water boils at a lower temperature. At the summit of Mount Everest, where the pressure is low, your water barely boils at 70°C, not great for cooking pasta! Conversely, the higher you increase the pressure, for example in a pressure cooker, the higher the water reaches a temperature (above 100°C) before boiling, which speeds up cooking.
The boiling temperature is the limit at which water changes from a liquid state to a gaseous state. At this point, even if you continue to heat, the temperature no longer rises: the energy is used to overcome the bonds between the molecules, not to heat further. This is what is called latent heat, the invisible energy that is only used to change state. As long as all the liquid water has not turned into steam, its temperature remains fixed around the famous 100 degrees Celsius at normal atmospheric pressure.
When you add salt to the water for your pasta, you slightly raise the boiling point. Why? Because impurities, like salt, hinder water molecules from transitioning to a gaseous state. Therefore, it needs to be heated a little more to reach boiling. This is called boiling point elevation. Conversely, some solvents or volatile substances can lower this point, making it easier for the water to turn into vapor. That’s why, depending on what you mix with the water, it doesn’t always boil exactly at 100°C!
Did you know that the pressure cooker directly utilizes the relationship between pressure and temperature? Due to the high internal pressure, the water in a pressure cooker reaches a temperature higher than 100°C before boiling, thereby speeding up the cooking time of food.
At high altitudes, such as at the summit of Mount Everest (about 8,848 meters above sea level), water boils at only about 69.9 °C due to the low atmospheric pressure! So be prepared to wait longer to cook your rice up there.
Tap water containing impurities (minerals, dissolved gases, various particles) can slightly alter its boiling point, but these variations remain very small (typically just a few tenths of a degree Celsius).
The phenomenon known as the 'Mpemba effect' reveals that, surprisingly, in specific cases and under certain circumstances, hot water can freeze faster than cold water! This counterintuitive phenomenon continues to intrigue scientists even today.
The salt added to water slightly raises its boiling point, allowing for faster and more even cooking of food. Additionally, it also enhances the flavor of the food.
These small bubbles are often air bubbles dissolved in the water, released by heating before reaching the boiling point. Actual boiling only occurs at 100°C under normal atmospheric pressure.
At normal atmospheric pressure, it is indeed impossible to heat pure liquid water beyond 100°C. At this temperature, any additional thermal energy will be used to convert the water into steam (evaporation) without increasing its temperature.
Yes, if we significantly reduce the surrounding pressure — for example, using a vacuum pump — it is possible to bring cold water to a boil without adding any additional heat.
Yes, by adding certain solutes (such as salt or sugar), it is possible to slightly increase the boiling point of water, a phenomenon known as boiling point elevation.
At high altitudes, atmospheric pressure decreases. As the pressure is lower, the boiling point also drops. Thus, at high altitudes, water boils at a temperature lower than 100 degrees Celsius.
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