b) 100°C steam is hotter than 100°C water
Answers
Answer:yes
Explanation:
yes it is
Answer:
No, not hotter because the temperature of the steam and boiling water are the same and it's 100 degrees celsius but steam contains much more energy than boiling water because it has latent heat.
Explanation:
There are 4 fine answers here, but I still want to throw in my 2 cents. There's a difference between "heat" and "heat transfer". Is steam hotter than boiling water? If both are at atmospheric pressure (14.7 psi), they are both at the temperature of 100C or 212F. So no, there is no difference in temperature.
As mentioned by other posters, if the pressure is increased, so will the boiling point. Therefore, hot water and steam at a pressure of 18.7 psi, just 4 psi increase, is at a boiling temperature of 224.4. So the temperature has increased, but it has increased for both.
To increase the temperature of steam above that of hot water, you would have to boil off all of the water and continue to add heat until it becomes "superheated", which means it is at a temperature above the boiling point. One example of this is a pressure cooker. The pressure cooker increases the pressure of the hot water/steam so it boils at a high temperature. Inside the vessel, the steam is at the same temperature as the water. But now the steam escapes out of the little port we have on top of the pressure cooker. It is now at a higher temperature but the pressure, and corresponding boiling temperature, has dropped to atmospheric levels. So if that steam was shooting out of the pressure cooker next to an open pot of boiling water on the stove, the steam would be at a higher temperature than the pot of boiling water...but only until it cooled off or was absorbed into the air.
That is temperature, now what about heat transfer? The energy necessary to turn a liquid into vapor is called the "Heat of Vaporization". That same energy is needed to be removed in order to condense a vapor back into a liquid. For water, the heat of vaporization at atmospheric pressure is 970 Btu/lb. In comparison, the definition of a BTU is the energy it takes to change 1 pound of water by 1 degree F.
So imagine this scenario, you stick your hand into a pot of boiling water that is no longer receiving heat from the stove. If your hand absorbs 1 BTU, the water will drop by 1 degree. Impossible scenario, I know, but if you were fast enough you probably wouldn't get much of a burn. In comparison, if you let 1 lb of steam condense on your skin, you will receive 970 Btu of heat and your hand will not feel good.
For further comparison, let's say you popped the little jiggler off the valve of the pressure cooker and let it vent steam straight out at 224F but atmospheric pressure. Now you stuck your hand in it and let 1 lb of that steam transfer enough energy into your hand to cool down to 212F...not condense, just cool down. That would transfer just under 6 BTU of heat to your hand. You probably wouldn't notice.
What's the point of all this? Well, many people feel that the steam off a boiling pot of water is "hott.er" than that steam whistling out of the pressure cooker. The pressure cooker steam is actually hotter, but it has a much lower heat transfer rate than the condensing steam. So the condensing steam seems hotter. The boiling water, in comparison, seems even hotter. In this case, it isn't that the heat transfer rate is higher, its because there is a much larger mass of hot water. It would take some time to wait for 1 lb of steam to condense on your hand but a pound of water can convect heat into your skin very quickly.
Just in case anyone is fo.olish enough, please don't try any of this at home. Sticking your hand into a pot of boiling water is just du.mb, even if it is for science.