Heat of Condensation
Definition and meaning of Heat of Condensation in chemistry.
Heat of condensation is the energy released when a gas becomes liquid. This change happens at a totally constant temperature and a constant pressure. The process is intensely exothermic because it gives off large energy amounts.
In more detail
Gas molecules bounce around wildly and hold a massive amount of energy. As vapor cools down, the fast molecules slow down significantly and cluster. They move close enough for strong intermolecular attractive forces to grab them.
Hydrogen bonds or van der Waals forces lock them into liquid drops. This reorganization releases the exact same energy initially used to vaporize them. The substance gives off this massive energy to the surroundings as heat.
Because this transfer happens at the boiling point, it is latent heat. The thermometer reading stays completely flat while the vapor turns to liquid. Engineers capture this released heat to generate electricity in massive power plants.
The condensing steam easily turns heavy turbines before returning to liquid water. Heat of condensation explains many powerful weather phenomena in our Earth's atmosphere. The warming effect of thick cloud formation comes entirely from this process.
Many students wrongly believe that condensing steam absorbs cold from the air. Condensing steam actually pumps its stored thermal energy outward into the air.
Key facts
| Symbol | ΔHcond |
|---|---|
| Typical units | kJ/mol or J/g |
| Relation | ΔHcond = −ΔHvap |
| Sign convention | Negative (exothermic) |
| Water (100°C, 1 atm) | −40.7 kJ/mol (−2257 J/g) |
| Field | Physical Chemistry |
Consider exactly one mole of hot steam at 100 degrees Celsius. When this 18.0 grams of vapor condenses, it releases 40.7 kilojoules of heat. This massive energy release is identical to water's molar heat of vaporization. This is exactly why steam burns are so incredibly dangerous for humans. The steam releases all its heat of condensation directly onto your skin. Then the resulting boiling liquid water cools down and burns you further. This double hit delivers far more total energy than boiling water alone.
Frequently asked questions
Why is heat of condensation negative while heat of vaporization is positive?
They describe the exact same phase change moving in two opposite directions. Vaporization absorbs energy to completely break all intermolecular attractions apart into gas. Condensation releases that identical amount of energy as those strong attractions reform.
Why do steam burns hurt so much more than boiling water burns?
Steam must first release its massive heat of condensation onto your skin. This delivers about 2257 joules of burning energy per gram of water. The resulting hot water then burns you more as it finally cools.
How does heat of condensation affect major weather systems and huge hurricanes?
Water vapor rising from the warm ocean condenses into high storm clouds. This condensation releases an enormous amount of latent heat into the atmosphere. This massive heat release powers the intense swirling winds of a hurricane.