What physical differences do water vapour and steam have other than water vapour having a lower temperature? How it is possible for it to exist in the air (I.e. during a hot shower, clouds) whilst being below the boiling point of water? Do the molecules look the same under a microscope?
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Steam is larger droplets of water, while water vapor is water in its actual gaseous phase and is completely invisible.
You have misconception about boiling point of water. In order for water to be in gas form it doesn’t have to be over boiling point of water. Boiling point of water is the point where water molecules overcome liquid-phase intermolecular forces so it turns into steam.
You can also overcome those forces with kinetic energy. It’s called evaporation. And it occurs at the surface of the liquid. Rate of evaporation depends on temperature and relative humidity of surrounding air and also movement of the air.
Vapour is a gas with a temperature lower the the critical temperature. That is the temperature where you no longer can condense it by increasing pressure, for water it is 374 °C; 705 °F Vater vapor is invisible.
Then what is steam it has multiple meanings.
A wet stream is a mixture of water as a gas and a liquid. The liquid part is a small water droplet. The liquid droplets are visible and this is what you see in the white steam you likly think about. The temperature will be below the critical temperature so the water as a gas it a liquid.
A liquid or solid suspended in air is called an aerosol.
Dry steam is when you have heated the water so it is just a gas and there are no liquid droplets present. This is invisible, If the temperature is below the critical temperature this is a vapor.
If the temperature is higher than the critical temperature it is a gas but not a vapor, If the pressure is higher then was required to condense it at the critical temperature it is a supercritical fluid.
So if we talk about temperatures below 374 °C then if you can see steam it is a vapour and liquid droplet mixed, if you can see it it i just a vapour.
Boiling points do not refer to the point whre a liquid CAN evaporate, it refers to the temperature at which it CANNOT STAY LIQUID.
Liquids may evaporate without reaching this critical temperature
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