If water boils at 100°C, and boiling is the process of turning liquid into gas, why are bathrooms full of steam when showering at only 40°C?
In: Chemistry
What you see in the bathroom isn’t actually steam. It’s water vapour – tiny blobs of liquid water.
Steam is water over 100°C (assuming you’re not really high up a mountain, or deep down in the ocean). It’s also see through. Look at the steam escaping from a kettle or the lid of a boiling pan of water. You’ll see a portion that’s see through. That’s the steam. When it cools slightly it becomes water vapour – the cloudy stuff.
Also worth noting that 0 degrees is the triple point of water where it can exists in all 3 states. One of them being steam
The white mists you see in showers aren’t steam. They’re most likely condensed water vapour/steam. You can’t technically see water in its gaseous state.
Which explains why you can see it, because the 40°C water will gain heat and evaporate into water vapour and then condense if the surrounding air is cooler. You most likely won’t be able to see it if the surrounding air is warmer.
Steam is an invisible gas. If your bathroom were filled with it you would be washing off more than dirt from your body, if you lived that long that is. Water vapour is what fills your bathroom and that can occur at a range of temperatures.
The issue is the definition of temperature. You’re using it in a way that makes it sound like “the object is at that temperature” and that’s what is confusing you.
Temperate is the AVERAGE kinetic energy per unit volume. If you measure actual kinetic energies at a molecular level, you’ll find they are spread out over a range of values. If you plot those, you get a curve called the Maxwell Boltzmann distribution. It has a big lump in the middle and a long tail of “hotter” bits. Due to the math, the temperature is in the middle of that lump, because that’s literally the definition.
So when you have water at, say, 30 degrees, this implies the average particle is energy is 30. If you plot that curve and then put a line at 100, you’ll notice there are still particles beyond that 100 line. Those will “boil” even though the water as a whole is well below the boiling point. If you increase the temperature to, say, 50, that curve moves and more and more of the particles are past the line and the rate goes up.
As you continue increasing the temperature, eventually you hit a point where the average particle has that amount of energy. At that point the rate of gasification is great enough that the water is seen to be bubbling en mass, or “boiling”. We call that 100C. Now the situation is reversed: removing heat at this point will leave you with the particles that were still below the boiling point, or were after the random processes.
Water evaporates at all temperatures. Clothes suspended in the sunshine still dry, even though the water temperature is nowhere near 100°C. The air contains evaporated water (we call that “air humidity”) from which the clouds form, even though the temperature is way below 100°C.
Even frozen water slowly evaporates through a process called sublimation.
Think of it like this: below 100°C water can be either gas *or* liquid. Above 100°C is gas only.
ELI5: All molecules in water are always moving chaotically, bumping into each other, changing direction, and so on. You can roughly think that the temperature of water is the speed of an average water molecule. (Strictly speaking, temperature is the average kinetic energy, which is the mass of a molecule times the speed squared.)
Imagine you are a molecule on the surface of the water. You can try to leave it (evaporate), but there are two forces that prevent this. First, other water molecules try to stop you and keep you inside. This is called intermolecular forces. Second, molecules of air also try to push you back. That’s why only strong and fast molecules (with high kinetic energy) can overcome both forces and actually leave the water (evaporate).
If only the fast molecules leave the water and the slow ones stay, the average speed of the remaining molecules gets lower, which means the temperature drops. This is why water cools down when it evaporates.
Now to the boiling point. The boiling point is when the average Joe of water molecules is fast enough (has enough kinetic energy) to overcome both forces and leave the water.
That’s water vapor, not steam. Like you said, steam is 100°C minimum, and would give you horrible burns!
The “steam” you see is actually liquid water droplets suspended in the air (a colloid). It’s more like fog or mist. Steam itself is invisible.
Because it’s not “steam”.
People use the word “steam” to mean two very different things:
1. The invisible gas that comes out of a boiling kettle, water in its gaseous form at 100ºC or higher. (Actual steam)
2. Water vapour visibly condensing from gas to tiny droplets when its temperature drops.
Bathrooms are not full of “steam” (1), you are seeing water vapour condensing (2). You can see it at lower temperatures, like when you breathe out on a cold morning.
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