MCQ Detailed View

Scalding with steam is more severe than scalding by boiling water because steam contains more heat energy than water at the same temperature. This additional energy is due to the latent heat of vaporization stored in steam.

Water boils at 100°C under normal atmospheric pressure. At this point, liquid water changes into water vapor (steam). To undergo this phase change, water absorbs a large amount of additional energy without a rise in temperature. This extra energy is called the latent heat of vaporization, which is approximately 2260 kJ/kg for water.

When steam comes into contact with human skin:

1. 
   

   It first condenses back into liquid water, releasing its latent heat.

   
   


2. 
   

   This energy is transferred to the skin almost instantly, causing more severe burns than boiling water at the same temperature.

   
   


3. 
   

   The condensed water remains at 100°C, continuing to transfer heat to the skin, worsening the injury.

   
   

The other options are scientifically incorrect:

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  Steam can penetrate the skin: This is not true; burns are caused by heat transfer, not penetration.

  
  


• 
  

  Steam is at a higher temperature: Both boiling water and steam are generally at 100°C under normal pressure.

  
  


• 
  

  Steam is at a higher pressure: Everyday scalding usually involves atmospheric steam, not high-pressure steam.

  
  

This principle explains why:

• 
  

  Industrial steam burns are extremely dangerous due to both high temperature and latent heat.

  
  


• 
  

  Cooking with steam transfers heat more efficiently than boiling because of this extra energy.

  
  

In thermodynamics, phase changes involve hidden energy that is not seen in temperature readings but plays a major role in heat transfer. Therefore, steam burns are more severe than boiling water burns because steam carries additional latent heat energy, which is released rapidly upon condensation on the skin.