why do a burn at 100 degrees C steam is more severe than a burn from water at 100 degrees C?

A really good question.

Burns or, more accurately, burn effects (blisters, redness, etc) are caused by heat, not temperature. The short answer is that steam at 100 C contains more heat than water at 100 C. Thus more, and more severe, burn effects come from the steam than from the water.

The reason steam has more heat, in the same amount of mass, is because water takes on additional heat to change from its liquid state into its gas state (i.e., into steam). That is, up to 100 C the heat raises the temperature of the water. But at 100 C, as the water changes to steam, more heat is added without changing the temperature.

That extra heat is called the heat of vaporization...it stays stored in the steam as a latent heat that will be released when the steam liquefies. And that extra heat is passed on into your body as the steam condenses on your skin. That extra, latent heat is why the burn effects are more severe.

When water at 100 degree C is converted into steam at 100 degree C, an additional heat energy of 540 Calories per gram of water is utilised. Hence, the energy possesed by steam is much higher than that of boiling water at 100 degree C. This additional energy (which is called "LATENT HEAT OF STEAM) is the cause of the severe burn.

Water at 100 C is a little bit cooler than steam at 100 C because there is still some heat in the water that has not been given up. This is called the heat of vaporization and is approximately equal to 2268 J.

When water turns to steam, then steam takes on this additional heat energy and this is the reason why steam at 100 C is "hotter" than water at the same temperature.

Either hot water or steam can give a nasty scald. However if a hand is placed into stagnant hot water (100C) the vibration of water molecules will vibrate skin molecules heating up the hand while cooling down the water. This will provide a barrier of 'cooler' water that protects the hand. If a hand is placed in live steam (100C) as the hand heats up steam condenses and drips away to be immediately replaced with more live steam and only a very thin film of hot condensed water forms giving nil protection.

100 Degrees Celsius

100 Degrees Centigrade

steam causes more severe burns because particles in steam at 100 C have more energy than water at the same temperature (latent heat). this is because steam absorbs extra energy in the form of latent heat of vaporisation.

In order for boiling water to turn into steam, in needs additional energy, called 'heat of vaporization'. In other words, if you raise the temperature of water to boiling point, it still needs extra energy to become steam. When the steam contacts your skin, it re-condenses into water, and releases this energy. Thus, the amount of heat given off by the steam when it contacts your body is more than the heat given off by the water.

Because water is a liquid and steam is a gas.when you touch the water that will be hunt you but steam without touch.

It is so because steam on cooling gives extra 2268Joules of energy called latent heat of vaporisation