Concept Explanation: Why Steam Causes More Severe Burns Than Boiling Water

Both steam and boiling water are at 100°C (at standard atmospheric pressure), but steam causes more severe burns. This is because steam contains additional latent heat of vaporization.

Step-by-Step Reasoning:

Step 1: Understand the heat energy in boiling water.

Boiling water at 100°C has heat energy that it can transfer to your skin, causing a burn. This heat is called sensible heat.

Step 2: Understand what steam is.

Steam is the gaseous form of water. To change boiling water (at 100°C) into steam (also at 100°C), a large amount of extra heat energy must be added. This extra energy is called the latent heat of vaporization.

The latent heat of vaporization for water is very high: $L_v=2257\mathrm{kJ}/\mathrm{kg}$

Step 3: Analyze the burn process.

When steam comes in contact with your cooler skin, two things happen:

1. It condenses back into liquid water. During this process, it releases all the latent heat of vaporization it was storing.
2. The resulting hot water (now at 100°C) then transfers its sensible heat to your skin.

Therefore, steam transfers a much larger total amount of heat energy to your skin compared to an equal mass of boiling water.

Step 4: Compare the total heat energy.

The total heat ($Q$) released by 1 kg of steam when it hits your skin and cools down is:

$$Q=L_v+(mc\Delta T)$$

where $L_v$ is the latent heat, $m$ is mass, $c$ is the specific heat capacity of water, and $\Delta T$ is the change in temperature. Boiling water only releases the sensible heat component $(mc\Delta T)$.

Final Answer: The correct option is latent heat of condensation. This is the term for the heat released when a gas (like steam) turns into a liquid. This immense amount of energy is what makes a steam burn much more severe.

Related Topics & Formulae

Latent Heat: The hidden heat energy absorbed or released during a phase change at constant temperature.

• Latent Heat of Vaporization ($L_v$): Heat needed to convert 1 kg of liquid into gas at its boiling point. $$Q=m{L}_v$$
• Latent Heat of Condensation: Heat released when 1 kg of gas condenses into a liquid. It is numerically equal to $L_v$.
• Latent Heat of Fusion ($L_f$): Heat needed to melt 1 kg of solid into liquid at its melting point.
• Latent Heat of Sublimation: Heat required to change 1 kg of solid directly into gas.

Sensible Heat: The heat energy that leads to a change in temperature, calculated by $Q=mc\Delta T$.