Question

Water at \(100^{\circ} \mathrm{C}\) (its normal boiling point) could certainly give you a bad burn if it was spilled on the skin, but steam at \(100^{\circ} \mathrm{C}\) can give you a much worse burn. Explain.

Short answer

Steam at 100°C causes more severe burns than water at the same temperature due to the large amount of heat energy released during the phase change (latent heat of vaporization) of steam condensing back into liquid, combined with the high specific heat capacity of water. While water at 100°C only imparts energy from its specific heat capacity, steam releases additional energy during condensation, resulting in more severe burns.

Step-by-step solution

Phase Change and Latent Heat

Water at 100°C is in its liquid phase, whereas steam at 100°C is in its gaseous phase. When a substance undergoes a phase change (such as turning from liquid to gas), it either absorbs or releases a specific amount of heat energy called latent heat. In the case of water turning into steam, it needs to absorb the latent heat of vaporization. When steam condenses back into water on the skin, this energy, called latent heat, is released. The latent heat of vaporization for water is quite significant at approximately \(2260 \frac{ J}{g}\). So, when steam at 100°C comes into contact with the skin, the steam undergoes a phase change (condensation) and releases a large amount of energy as it transfers from gas to liquid. This extra energy is effectively being imparted to the skin and results in more severe burns.

Specific Heat Capacity

Specific heat capacity is the amount of heat energy required to raise the temperature of one gram of a substance by 1°C. Water has a relatively high specific heat capacity of approximately \(4.18 \frac{J}{g^{\circ}C}\). This means that liquid water can absorb or lose a considerable amount of heat before its temperature changes by a significant amount. When water at 100°C comes in contact with the skin, it will lose heat energy to the skin. This loss of heat will cause the water's temperature to decrease, and as a result, less energy is transferred to the skin as compared to steam.

Combining Factors

Steam at 100°C causes more severe burns because it releases a large amount of heat energy (latent heat) when it condenses back into the liquid phase and combines this with the energy it has due to its high specific heat capacity. In contrast, liquid water at 100°C only has energy due to its specific heat capacity. In summary, the main reasons for steam causing more severe burns than water at the same temperature of 100°C are the additional heat energy released during the phase change (latent heat of vaporization) and the high specific heat capacity of water.

Key concepts

Latent Heat

Latent heat is a fascinating property of substances that plays a crucial role during phase changes—when a material shifts from one state of matter to another, such as from liquid to gas or vice versa. This type of heat doesn't cause a change in temperature. Instead, it goes into altering the structure of the material as it changes phases.
For example, when water is heated and becomes steam, it absorbs a significant amount of energy known as the latent heat of vaporization. Conversely, when steam condenses back into water, it releases that same amount of energy.

• Latent heat is involved in phase changes such as melting, freezing, boiling, and condensation.
• This energy is what makes steam at 100°C more dangerous than liquid water at the same temperature.

The additional energy released as latent heat can cause much more severe burns, as it gets transferred to human skin, making it crucial to understand this concept when dealing with substances at their phase change points.

Specific Heat Capacity

Specific heat capacity is a measure of how much heat energy is required to raise the temperature of a substance by one degree Celsius. Water, for example, has a high specific heat capacity, meaning it can trap and hold a lot of heat energy before its temperature rises or falls significantly.
This property is key to understanding how heat is transferred between substances. When water is at 100°C and comes into contact with skin, it will transfer heat energy to the skin until the temperatures equalize.

• The specific heat capacity of water is approximately 4.18 J/g°C.
• This means water can both absorb and release significant amounts of energy without a big change in temperature.

This characteristic explains why water can seem hotter than expected—it holds a lot of energy. But it's the combination of high specific heat capacity and latent heat during steam condensation that makes steam particularly potent in heating skin.

Latent Heat of Vaporization

The latent heat of vaporization is the specific amount of energy needed for a liquid to change into a gas without a temperature change. For water, this value is quite high, at about 2260 J/g, underscoring how much energy water must absorb to become steam—and how much it releases when going back to liquid.
When steam at 100°C contacts your skin, it undergoes condensation, releasing this latent heat of vaporization. This energy release adds to the severity of burns that steam can cause.

• The latent heat of vaporization involves no change in temperature but a change in state.
• It's a critical factor in understanding the energy dynamics of systems involving phase changes.

The latent heat of vaporization is why steam can release much more energy into your skin than hot water, intensifying the burn potential when exposed to steam.