Why is water boiling in space

Why does water boil faster on Mount Everest than here?

Water evaporates at any temperature, at any altitude. Water vapor is created. From a certain temperature, at a certain altitude, the air pressure in the surroundings is equal to the air pressure in the vapor bubbles in the liquid. It bubbles. They say the water is boiling. The lower the air pressure, the lower the boiling temperature. At the top of Mt. Everest, the air pressure is so low that the water boils at 70 degrees Celsius.

A liquid can evaporate like this. The most energetic particles on the surface can leave the liquid as vapor. This already happens at room temperature - after a few days a water bowl is empty.

But at a certain temperature a new process begins, in the liquid itself there are vapor bubbles which rise to the surface, these now have the same pressure as the surrounding air. They rise and disappear in the air. The temperature at which this occurs is called the boiling point.

Latent heat: when the temperature does not rise

Despite further heating, the temperature in the water now remains unchanged. So: from the boiling point, the temperature no longer increases.

Since it is not the funny, bubbling boiling water that counts when cooking, but the temperature, it cooks worse on Mount Everest. The potatoes only get 70 ° warm in the boiling water.

The boiling temperature depends on the ambient pressure. One detail: the air pressure decreases exponentially, it halves every 5500 meters.

In short: the air pressure determines the temperature at which a liquid boils. The lower the air pressure, the lower the boiling temperature. On Mount Everest, the boiling temperature is only around 70 ° C, depending on the weather (fluctuations in air pressure) the value fluctuates by 10%.

Tip 1: Whether on Mount Everest or at home on the stove: Put the lid on the pot - and you can save energy because the energy-rich (hot) water molecules stay in the pot. The water boils faster by 1/3 when the lid is on the pot.

Tip 2: Greater pressure is created in a pressure cooker. The boiling temperature of water in it is about 130 ° Celsius. The potatoes will cook faster.

It is noteworthy that during boiling the temperature of a liquid does not rise any further if you continue to heat it. Since the cooking time now depends on the temperature when cooking food - and not on the funny pearls that rise when it simmered, one thing is clear: at 70 ° C on Mount Everest it takes longer to cook a dish than in a pressure cooker at 130 ° C, it's faster.

Wikipedia keywords: air pressure, boiling, phase transition


Photo by Michael Clarke on Unsplash