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Latent Heat of Steam
Latent heat of steam, also known as latent heat of vaporization of water, is the amount of heat energy required to convert water into steam without changing its temperature.
When water is heated, its temperature increases until it reaches 100°C (212°F) at atmospheric pressure (1 atm). Beyond this point, additional heat does not raise the temperature further but is instead used to change the liquid into steam. This absorbed energy, required to overcome the molecular forces holding water molecules together, is called latent heat.
Why is It Called “Latent” Heat?
The word “latent” means hidden. This heat is called latent because it does not cause a temperature change, even though energy is being absorbed. Instead, it is used to convert liquid water into steam.
Key Facts About Latent Heat of Steam
- At 100°C and 1 atm, the latent heat of steam is 2260 kJ/kg (kilojoules per kilogram) or 540 cal/g (calories per gram).
- This means that 2260 kJ of heat energy is required to convert 1 kg of boiling water into steam.
- During the phase change, the temperature remains constant at 100°C.
- The same amount of heat is released when steam condenses back into liquid water.
Why is the Latent Heat of Steam So High?
Water has one of the highest latent heats of vaporization among common substances. The main reasons are:
1. Strong Hydrogen Bonding in Water
Water molecules are held together by hydrogen bonds, which require a large amount of energy to break.
- These bonds form due to the attraction between oxygen (negative charge) and hydrogen (positive charge) in adjacent water molecules.
- To convert water into steam, these intermolecular forces must be completely broken, requiring extra energy.
2. High Molecular Cohesion
Water molecules are highly attracted to each other due to their polarity.
- More heat energy is required to overcome these attractive forces and allow molecules to move freely in the gaseous state.
3. High Specific Heat Capacity of Water
Water has a high specific heat capacity, meaning it can absorb a lot of heat before its temperature increases.
- This property contributes to its high latent heat, as a large amount of energy is required to change its phase.
4. Steam as an Efficient Heat Carrier
Because steam holds so much latent heat, it is widely used in:
- Power plants (to drive turbines for electricity generation)
- Heating systems (to transfer large amounts of heat efficiently)
- Industrial processes (such as sterilization and food processing)
How is Latent Heat of Steam Calculated?
The amount of heat required for a phase change can be calculated using the formula:
Q = m × L
Where:
- Q = Heat energy (Joules or kJ)
- m = Mass of water (kg or g)
- L = Latent heat of vaporization (2260 kJ/kg or 540 cal/g)
Example Calculation:
If 2 kg of water at 100°C needs to be converted into steam, the required heat is:
Q = 2 × 2260
Q = 4520 kJ
This means 4520 kJ of heat is needed to completely convert 2 kg of boiling water into steam at 100°C.
Why is Latent Heat of Steam Important?
1. Steam Engines and Power Plants
- Steam is used in thermal power plants to generate electricity.
- The high latent heat of steam allows efficient energy transfer in power systems.
2. Cooking and Food Processing
- Steam is used in steamers, pressure cookers, and sterilization.
- The large heat capacity of steam helps cook food quickly and evenly.
3. Industrial Applications
- Steam is used in chemical industries, textile processing, and paper manufacturing.
- It provides heat for drying, sterilization, and chemical reactions.
4. Weather and Climate
- Water evaporates from oceans, lakes, and rivers by absorbing latent heat from the sun.
- This energy is released back when water vapor condenses into clouds, driving rainfall, storms, and hurricanes.
Common Questions About Latent Heat of Steam
How is Latent Heat Different from Sensible Heat?
- Latent Heat is the heat energy required for a phase change without temperature change (e.g., water to steam at 100°C).
- Sensible Heat is heat energy that raises temperature but does not change phase (e.g., heating water from 50°C to 100°C).
Also Check – What is Latent Heat? Fusion & Vaporization Explained with Real-Life Applications
Why Does Steam Burn More Than Boiling Water?
- Steam carries more heat energy than boiling water because of its latent heat.
- When steam touches the skin, it condenses back to liquid, releasing all its stored heat at once, causing severe burns.
Also Check – Why Steam Burns Are More Dangerous Than Boiling Water Burns – in Details
Does the Latent Heat of Steam Change with Pressure?
- Yes. When pressure increases, the boiling point of water rises, and the latent heat decreases.
- In a pressure cooker, water boils at a higher temperature, cooking food faster with less latent heat required for steam formation.
