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∘C, are cooled down to skin temperature, 34∘C when they come in contact with your skin. Assume that the steam condenses extremely fast. The heat capacity of liquid water is c=4190J/(kg⋅K) for both liquid water and steam.
How much heat H1 is transferred to the skin by 25.0 g of steam onto the skin? The latent heat of vaporization for steam is L=2.256

Answer 1

Answer:

H1 = 63.3 kJ

Explanation:

Given:

ΔL = 2.256 kJ/g

Cp = 4190J/kg⋅K

Steam at 100°C in contact with your skin, condenses to water at 100°C. Therefore,

Q = M × ΔL

= (25.0 g)(2.256 kJ/g)

= 56.4 kJ

This condensed water at 100°C is then cooled to 34°C. The heat involved with this temperature change is;

Q = m × Cp × ΔT

= (25 × 1kg/1000g × 4190 × (100°C - 34°C)

= 6913.5 J

= 6.914 kJ

The total heat H1,

= (56.4 kJ) + (6.9135 kJ)

= 63.3 kJ.