For example a 40°c shower can turn water into water vapour even though the boiling point is 100°C
In: Chemistry
Water can go to vapor (which is the better term than steam here) at almost all temperatures, as long as the environment is not too humid.
That is called evaporation (while at 100°C the water is boiling).
Basically this works, because there are always some of the water particles fast enough (have enough energy), to leave the liquid and become vapor. With increasing temperature there are just more water particles which can do this, until at 100°C almost all particles can go to steam very quickly.
The remaining liquid cools down, when water evaporates (because it looses energy). That is the reason sweating cools us down. The sweat evaporates and cool downs our skin. And as you can see there, this works at every temperature.
“Steam” in a steamy shower is not the same thing as stream in like a steam engine. The steam you can see is actually tiny droplets of liquid water suspended in the air: it’s the same stuff as clouds or fog.
Air is a mixture of mostly oxygen and nitrogen with some water vapor (and other gasses) mixed in. The water vapor is called humidity. Hot air can hold more water than cold air, so in a steamy shower, hot humid air mixes with colder air in the rest of your bathroom and some of the humidity condenses out into tiny droplets which is “steam” you can see.
Boiling is when liquid water is so hot that it instantly turns to vapor at ambient pressure. But evaporation—slowly turning into vapor—happens at much lower temperatures. You might know evaporation by its more common term: “drying.”
Water is made up of water molecules. Little bouncy ball like things that fly around at speed. The more heat you put in the faster the molecules go. If they go fast enough they have enough power to escape from the water and become steam.
However not all the the molecules are going at the same speed, some are going fast and others slow. So at any temp the really fast ones are going to be fast enough to escape. This forms a little space above the water where there are a lot of water vapor. Some of this gets pulled back into the water and other escapes and floats around your bathroom.
What the boiling point is, is the temp where there are enough water molecules going fast enough that the it can escape out and cool the water so it can’t get any hotter.
Water turns into steam at 40°C because that is the temperature at which the vapor pressure of water equals atmospheric pressure. This means that the water molecules have enough energy to escape into the air as steam.
To be even simpler than some.of the other (correct) answers here:
Water vapour is not steam.
Steam is completely invisible, and you only get that made at high temperatures. Water vapour makes clouds of stuff that you can see, and can be made at much lower temperatures.
The confusion comes when you have invisible steam coming out of a kettle and it turns into vapour when it hits the cooler air and becomes visible as vapour.
Your shower is making vapour, not steam.
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