Final answer:
To turn 400 g of snow at -5°C into water at 37°C, the body must supply 195416 J of heat. This involves melting the snow and then raising the temperature of the water. Consuming snow directly can induce hypothermia, which is why it is not recommended in survival situations.
Step-by-step explanation:
The question requires a calculation of the amount of heat that the human body would need to provide to turn 400 g of snow at -5°C into water at body temperature (37°C). To solve this, you need to account for the heat required to melt the snow (the heat of fusion) and then to raise the temperature of the resulting water to body temperature. The heat of fusion of water is 334 J/g, and the specific heat capacity of water is 4.18 J/g°C.
Firstly, to melt the snow:
Heat needed to melt snow = mass × heat of fusion
= 400 g × 334 J/g
= 133600 J
After melting, the water will be at 0°C. Now, to heat it to body temperature:
Heat needed to raise temperature = mass × specific heat capacity × temperature change
= 400 g × 4.18 J/g°C × (37°C - 0°C)
= 400 g × 4.18 J/g°C × 37°C
= 61816 J
Thus, the total heat the body would have to supply is:
Total heat supplied by body = Heat needed to melt snow + Heat needed to raise temperature
= 133600 J + 61816 J
= 195416 J
Eating snow directly forces your body to produce this substantial amount of heat energy, which can accelerate hypothermia in a survival situation. Hence, the survival guide advises against it. This calculation underscores the reason why it's better to heat the snow on a stove rather than consuming it directly.