Question

Why does water vapor at \(100^{\circ} \mathrm{C}\) cause a more severe burn than liquid water at \(100^{\circ} \mathrm{C}\) ?

Short answer

Water vapor at 100 °C causes more severe burns due to the release of latent heat during condensation.

Step-by-step solution

Understanding the Concept of Temperature and Heat

Both water vapor and liquid water can be at the same temperature, in this case, 100°C. Temperature is the measure of the average kinetic energy of molecules.

Latent Heat of Vaporization

Water vapor contains additional energy in the form of latent heat, which is the energy required to turn liquid water into vapor at the same temperature. For water, this latent heat of vaporization is 2260 J/g.

Energy Transfer upon Condensation

When water vapor comes into contact with skin, it releases its latent heat as it condenses back into liquid water. This additional energy is transferred to the skin, causing a more severe burn.

Comparing Energy Transfers

Liquid water at 100 °C will transfer less energy to the skin compared to water vapor condensing on the skin because it lacks the extra latent heat that water vapor possesses.

Conclusion

Water vapor at 100 °C causes more severe burns than liquid water at the same temperature because the vapor releases additional latent heat when it condenses.

Key concepts

Temperature and Heat

Understanding why water vapor at 100°C burns more severely than liquid water at the same temperature begins with grasping the concepts of temperature and heat.
Temperature is a measure of the average kinetic energy of the molecules in a substance. In simple terms, it's a way to describe how hot or cold something is.
Heat, on the other hand, is the energy transferred between substances or systems due to a temperature difference. In our case, both water vapor and liquid water are at 100°C, meaning their molecules have the same average kinetic energy. However, the amount of energy they can transfer to your skin differs significantly.
When the skin comes into contact with a hot substance, heat energy is transferred to the skin, raising its temperature. This transfer can cause tissue damage and lead to burns.

Latent Heat of Vaporization

The key to understanding the difference in burn severity lies in the latent heat of vaporization.
Latent heat of vaporization is the energy required to turn liquid water into water vapor without changing its temperature. For water, this value is 2260 J/g, which is a lot of energy.
This energy is stored in the water vapor as latent heat. It allows the water molecules to separate from each other and spread out into a gas.
This energy is crucial because when water vapor condenses on your skin, it releases this 2260 J/g of energy back into your skin, significantly increasing the amount of energy transferred compared to a similar amount of liquid water.
That extra energy can cause greater tissue damage and more severe burns.

Energy Transfer

The energy transfer is essentially what determines the severity of the burn.
When water vapor at 100°C comes into contact with your skin, it undergoes condensation, switching from a gas back to a liquid.
During this process, it releases the stored latent heat, which is then transferred to your skin. So, in addition to the heat due to the temperature of the vapor, your skin absorbs this latent heat as well.
This means your skin receives much more energy from the water vapor than it would from liquid water at the same temperature.
As a result, burns caused by water vapor can be much more severe than burns caused by hot liquid water.