Question

Just about everyone at one time or another has been burned by hot water or steam. This problem compares the heat input to your skin from steam as opposed to hot water at the same temperature. Assume that water and steam, initially at 100, are cooled down to skin temperature, 34, when they come in contact with your skin. Assume that the steam condenses extremely fast. We will further assume a constant specific heat capacity for both liquid water and steam. Under these conditions, which of the following statements is true? A. Steam burns the skin worse than hot water because the thermal conductivity of steam is much higher than that of liquid water. B. Steam burns the skin worse than hot water because the latent heat of vaporization is released as well. C.Hot water burns the skin worse than steam because the thermal conductivity of hot water is much higher than that of steam. D.Hot water and steam both burn skin about equally badly.

Answer 1

Answer:

B. Steam burns the skin worse than hot water because the latent heat of vaporization is released as well.

Explanation:

It is given that both steam and the boiling water when in contact with the skin cools down from 100 to 34 degrees Celsius.

For any substance of mass m, the heat required to change the temperature by $\Delta T$ is $mC\Delta T$ (S.I. unit = Joules).

where C, the specific heat capacity is the same and a constant for both the condensed steam and the boiling water.  

But, there is a "hidden" energy (heat) released by the steam called latent heat

(given by mL, L = specific latent heat) which allows the phase transition (gas to liquid). While both of them are at the same temperature, their energy (heat) is different, which is why steam causes burns worse than boiling water