Final answer:
A burn from steam at 100 °C is more severe than a burn from boiling water at the same temperature because steam contains additional latent heat of vaporization, releasing more energy when it condenses, and can cover a larger area of the skin.
Step-by-step explanation:
A burn from steam at 100 °C is expected to be more severe than a burn from boiling water at the same temperature because steam contains more heat energy due to the latent heat of vaporization. When water boils, it absorbs a significant amount of energy to change from a liquid to a gas without increasing its temperature. Specifically, for water, this latent heat is 22.6 kJ/mol, which is a sizable amount compared to the energy required to heat the water up to 100 °C. Therefore, when steam contacts the skin, it releases more energy as it condenses back into water than the liquid water would deliver, causing a more severe burn.
Additionally, steam at 100 °C occupies more volume than the equivalent mass of liquid water and hence it has the potential to cover a larger area of the skin, which can increase the severity of a burn. In the context of an open pot, boiling water at 100 °C will eventually boil away because the ambient pressure is shared with air, and the pressure of the water vapor alone does not equate to the total atmospheric pressure, allowing the liquid to continue vaporizing.
For comparison, other liquids, like ethanol, may have weaker hydrogen bonding and thus require less energy to boil. Their steam would typically cause less severe burns than steam from water at the same temperature because they absorb less heat during vaporization.