Question

Why does water vapour at${\mathbf{100}}^o\mathbf{C}$cause a more severe burn than liquid water at${\mathbf{100}}^o\mathbf{C}$?

Short answer

The water vapour at ${\mathbf{100}}^o\mathbf{C}$causes a more severe burn than the liquid water at the same temperature because as the vapour comes in contact with the skin, it gets condensed. This process involves the release of heat energy and thus the vapour effect is more than the liquid form.

Step-by-step solution

Step-1: Condensation process 

When the vapour comes in contact with the any cool surface, the process of condensation takes place which involves the conversion of gaseous form to liquid form. The condensation reaction is anexothermic process and thus releases heat energy.

Step-2: Effect on Skin

As the water vapour at ${\mathbf{100}}^o\mathbf{C}$touches human skin (acts as a solid surface), the condensation processtakes place. The release in heat energy gives more itchiness and thus severe burn.

When the same burn takes place with liquid water atthere is no such release of heat energy, thus the burn is comparatively less severe.