Question

Which causes a more severe burn: liquid water at \(100^{\circ} \mathrm{C}\) or steam at \(100^{\circ} \mathrm{C}\) ? Why?

Short answer

Steam at 100°C causes a more severe burn than liquid water at 100°C due to the additional latent heat of vaporization.

Step-by-step solution

Understand the Question

The question is asking to compare the severity of burns between liquid water and steam both at the same temperature of 100°C. Understanding the properties of phase changes and the concept of heat transfer is critical here.

Consider the Energy Transfer in Liquid Water

Liquid water at 100°C transfers heat to the skin based on its specific heat capacity. The specific heat capacity of water is approximately 4.18 J/g°C. When in contact with skin, the heat energy transferred is determined by the mass of the water and the temperature difference.

Understand Steam and Its Latent Heat

Steam at 100°C not only has the energy equivalent to water at 100°C, but it also includes latent heat of vaporization. The latent heat of vaporization for water is 2260 J/g. This means when steam comes in contact with the skin and condenses into water, it releases a substantial amount of heat in addition to the heat it already possesses.

Compare Heat Transfer Between Liquid Water and Steam

When considering burns, the severity is determined by the total heat energy transferred. Steam at 100°C transfers both the latent heat of vaporization and the heat due to its temperature. Therefore, the total heat transferred by steam is the sum of the heat from condensing and the heat of the resultant water.

Conclude Based on Energy Transfer

Steam at 100°C causes a more severe burn compared to liquid water at 100°C because steam has higher energy content due to latent heat of vaporization and transfers more heat upon contact.

Key concepts

latent heat of vaporization

The concept of the latent heat of vaporization is crucial in understanding why steam causes more severe burns than liquid water, even if both are at the same temperature of 100°C. Latent heat is the energy required to change the phase of a substance without changing its temperature. For water, the latent heat of vaporization is 2260 J/g. This means that when steam at 100°C comes in contact with the skin and condenses into liquid water, it releases 2260 J of energy for each gram of steam, on top of the energy it already carries due to its temperature.

specific heat capacity

Specific heat capacity refers to the amount of heat needed to raise the temperature of a unit mass of a substance by one degree Celsius. For water, the specific heat capacity is 4.18 J/g°C. This property helps us understand how much heat liquid water at 100°C will transfer to the skin. When water at this temperature contacts the skin, it will transfer its thermal energy according to its specific heat capacity and temperature difference. Although significant, this heat transfer by liquid water is less than the combined heat released by steam due to latent heat and temperature energy.

energy transfer

Energy transfer in this context refers to the movement of heat energy from steam or liquid water to the skin, potentially causing burns. Steam at 100°C has two components of energy transfer: the heat associated with its temperature and the latent heat of vaporization. As steam condenses into water on the skin, it releases a large amount of energy due to the latent heat. Then, as this water cools down from 100°C to skin temperature, it further transfers heat, making the burn more severe. Meanwhile, liquid water at 100°C only transfers heat according to its specific heat capacity, resulting in less severe burns.