Steam is formed at 100°C but I see “steam” being produced at less than that temperature. What is that and why isn’t it steam?
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What’s special about 100° C?
At 100° C at sea level, the temperature of the water stops rising.
Instead, all the energy being pumped into the water gets used to convert that water to steam.
The water stays at 100° C until it is all turned to steam, and only then will the temperature begin rising again, up to over 2,000° C – – at which point it starts to break down (hydrolyze) into hydrogen and oxygen gases.
That’s why you can boil water over a campfire in a paper cup, and also why you can light a match with superheated steam.
My understanding is that steam is an invisible gas which you will get when you heat water up enough, the stuff you can see is water vapour which rather than being a gas is actually lots of extremely small water droplets suspended in the air. So, if you can see it, it ain’t steam.
Lets make this question more precise – “I’m heating water in a pot on the stove, with a thermometer submerged in it, and seeing visible evaporation prior to the thermometer showing 100c. Why?”
There are dozens of reasons here, because of the imprecision of your experiment, the variables of altitude, ambient temperature, humidity, and more.
Lets just take one – liquids being heated do not heat evenly. This is a particular problem in precision chemical reactions, which is why stirring, pebble beds, etc, are part of patented processes.
So you really can’t even say that the visible evaporation you’re seeing isn’t from 100c water, never mind the other variables that would cause it
Lets make this question more precise – “I’m heating water in a pot on the stove, with a thermometer submerged in it, and seeing visible evaporation prior to the thermometer showing 100c. Why?”
There are dozens of reasons here, because of the imprecision of your experiment, the variables of altitude, ambient temperature, humidity, and more.
Lets just take one – liquids being heated do not heat evenly. This is a particular problem in precision chemical reactions, which is why stirring, pebble beds, etc, are part of patented processes.
So you really can’t even say that the visible evaporation you’re seeing isn’t from 100c water, never mind the other variables that would cause it
If you have an electric kettle, take a look directly above the spout as it’s boiling – you’ll see a separation between top of the spout and the plume of vapour – that’s steam. It’s transparent. Steam is water in gas form. That plume you see is NOT steam, it’s water vapour, that’s liquid water in an aerosolised microdroplet form. As the gas steam meets the cooler air it rapidly condenses back into liquid droplets forming the vapour. Most people mistake water vapour, that cloudy plume, for steam.
Steam is actually pretty nasty stuff – can cause severe burns, even worse than boiling water since it often has a force component to it. Can cause rapid changes, both positive and negative (as it cools) in pressure vessels leading to catastrophic failures.
If you have an electric kettle, take a look directly above the spout as it’s boiling – you’ll see a separation between top of the spout and the plume of vapour – that’s steam. It’s transparent. Steam is water in gas form. That plume you see is NOT steam, it’s water vapour, that’s liquid water in an aerosolised microdroplet form. As the gas steam meets the cooler air it rapidly condenses back into liquid droplets forming the vapour. Most people mistake water vapour, that cloudy plume, for steam.
Steam is actually pretty nasty stuff – can cause severe burns, even worse than boiling water since it often has a force component to it. Can cause rapid changes, both positive and negative (as it cools) in pressure vessels leading to catastrophic failures.
Ok, first, what is temperature? Temperature is a measure of thermal energy. What is thermal energy? A simple way to look at thermal energy is as the energy contained within the random movement of the molecules. The faster the water molecules move in random directions, vibrations etc. the higher the temperature. Now, this is a statistical measure, specifically the average of a sample. This means that some molecules in a sample are going to be less or more energetic. Single particles or molecules do not have a temperature.
In practice this means that you will always have some water molecules with enough energy to escape the confines of their liquid prison. This is why water evaporates at temperatures below boiling point.
As we heat water, and the average energy of the molecules increases, more molecules are able to evaporate. Boiling point (100°C) is special. Were we to draw a chart with the amount of energy we are dumping into the water and the resulting temperature we would see a flat section. This is because at this point all of the additional energy is going directly into “yeeting” water molecules out of their liquid prison as they have already reached the maximum energy that they can have as a liquid.
Ok, first, what is temperature? Temperature is a measure of thermal energy. What is thermal energy? A simple way to look at thermal energy is as the energy contained within the random movement of the molecules. The faster the water molecules move in random directions, vibrations etc. the higher the temperature. Now, this is a statistical measure, specifically the average of a sample. This means that some molecules in a sample are going to be less or more energetic. Single particles or molecules do not have a temperature.
In practice this means that you will always have some water molecules with enough energy to escape the confines of their liquid prison. This is why water evaporates at temperatures below boiling point.
As we heat water, and the average energy of the molecules increases, more molecules are able to evaporate. Boiling point (100°C) is special. Were we to draw a chart with the amount of energy we are dumping into the water and the resulting temperature we would see a flat section. This is because at this point all of the additional energy is going directly into “yeeting” water molecules out of their liquid prison as they have already reached the maximum energy that they can have as a liquid.
a thing has got a state of aggregation, that means, it is solid, fluid, gas or plasma (like a flame for example). every thing can have different states of aggregation, water can be ice, water or steam. to change from one state to another, a big amount of energy is necessary. we dont realize it when water melts, because we do not feel hot at temperatures that melt ice, but in fact we are.
now if water turns into steam, the energy inside the pot is not the same everywhere. the water moves up, colder and hoter water mix up and than there are areas where there is enough energy to jump from fluid to steam and other areas, where it is not hot enough.
its a little bit like doves on the ground picking food and than a crow flies over them. the doves that are near to the crow feel fear first, so they start first flying away, while the others see the crow later and stay longer. the crow is the energy that is necessary to make the doves start.
To add to what others are saying about water vapor vs. steam, unless you’re beign super exact, 100 degrees is the *average* temperature. Local pockets may be more or less as they get closer to or further away from a heat source. It’s possible you’re really seeing a bit of steam that hasn’t cooled down yet.
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