superheated steam pressure temperature chart

So the blob takes on a volume about as small as it can get without the molecules smashing into each other. At very short range, the molecules repel each other- you can think of them as 'touching'. It's much easier to stick to a blob of other molecules than to stick to just one or two, so the choice is all or nothing: either the molecules form a big liquid blob or a free gas, not something in between. When they aren't too hot, they tend to stick to each other. So the question becomes why is there a liquid and why is it so small but not smaller? A quick answer is that the molecules attract each other. Why does the volume go up times 1700 when the liquid water boils to vapor at 212☏? We basically understand the gas volume by our simple pV=NkT argument. There are more fundamental and elegant ways to derive this, but I think this way is good for building physical intuition. It's also proportional to how much momentum they transfer on each hit, which is proportional to mv. Saturated steam is water at a temperature no greater than its boiling point at a designated pressure, i.e. Superheated steam is water at a temperature greater than its boiling point at a designated pressure, i.e. The average force on a wall (pressure times area) is proportional to how often molecules hit it, which goes as their speed v. The following specific properties are for superheated steam, as opposed to saturated steam. Why does the pressure go up about proportional to the absolute T? T is, in this range, a measure of how much translational kinetic energy (mv 2/2) the molecules have. So let's convert the T's to absolute tempratures in Kelvin: 373 K and 811 K. Water vapor at atmospheric pressure in this temperature range is close to being an ideal gas, for which V=NkT/p, where N is the number of molecules, k is a constant, T is the absolute temperature, and p is the pressure. The difference between 212☏ and 1000☏ (a volume ratio of 4200/1700=2.5, according to your numbers) is the easiest to understand. There are many ways to understand the effect. So the expansion you describe is purely due to how as the temperature goes up, while the pressure is held fixed, the volume goes up. If you don't specify the pressure, you don't know how much the expansion is. Those expansion ratios of water vapor compared to liquid water are all taken at fixed pressure.

Superheated steam pressure temperature chart