Burns produced by steam at 100°C are much more severe than those produced by the

Question

Burns produced by steam at 100°C are much more severe than those produced by the same mass of 100°C water. To verify this:

(a) Calculate the heat that must be removed from 4.00 g of 100°C water to lower its temperature to 53.0°C.

(b) Calculate the heat that must be removed from 4.00 g of 100°C steam to condense it and lower its temperature to 53.0°C.

(c) Calculate the mass of human flesh that the heat produced in each case can raise from the normal 37.0°C to 53.0°C. (Flesh is badly damaged at 50.0°C.)
steam
kg
water
kg

Explanation / Answer

part a)

specific heat of water , S = 4.186 J/(gm.degree C)

heat removed from the water = m * S * (T2 -T1)

heat removed from the water = 4 * 4.186 * (100 - 53)

heat removed from the water = 787 J

b)

latent heat of vapourization , Lv = 2260 J/gm

heat removed from the steam = m * (Lv + S * (T2 -T1))

heat removed from the steam = 4 * (2260 + 4.186 * (100 - 53))

heat removed from the steam = 9827 J

c)

Specific heat of body , Sb = 3500 J/kg.degee C

for the heat of water

m * (3500 * (53 - 37)) = 787

m = 0.0140 Kg

the mass of flesh that can be raised to this temperature is 0.0140 Kg

for the steam

m * (3500 * (53 - 37)) = 9827

m = 0.175 Kg

the mass of flesh that can be raised to this temperature is 0.175 Kg

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