Energy is transferred between a system (such as the flask with its water in it) and the surroundings as heat.
If you heat liquid water using a stove, heat energy is transferred from the stove element to the liquid water.
If you cool liquid water in the freezer, the heat energy is transferred from the liquid water to the freezer.
Why is steam so hot???
You probably have never observed that freezing releases heat energy, but you will have observed that condensation of steam releases heat energy if you have ever stuck your hand into the steam above a pot of boiling water. The steam condenses on your hand and releases heat energy to give you a nasty burn.
How is evaporation different from boiling?
Water puddles disappear after it rains. This is not due to boiling but to evaporation. Evaporation occurs because the water at the surface of the puddle gets enough heat energy from the sun to vaporise. The vapour mixes with the air and is blown away by the wind.
There is actually some vapour (gas) above the surface of the liquid in the stoppered flask above. It the stopper were removed, the liquid would evaporate because the vapour can mix with the air.
Acknowledgement: Most of the questions in the next section of this module are from Yezierski, Ellen J.; Birk, James P. J. Chem. Educ. 2006, 83, 954.
If you heat liquid water using a stove, heat energy is transferred from the stove element to the liquid water.
Heat is transferred from the surroundings to the system.
The system (liquid water) is said to absorb the energy.
The system (liquid water) is said to absorb the energy.
If you cool liquid water in the freezer, the heat energy is transferred from the liquid water to the freezer.
Heat is transferred from the system to the surroundings.
The system (liquid water) is said to release energy.
The system (liquid water) is said to release energy.
 | melts on heating   freezes on cooling |  | vaporises on heating condenses on cooling |  |
| increasing energy of system | ||||
The flask containing all of the gas derived from the liquid sample would be MUCH larger than the one shown.
Similarly if the gas in that flask is condensed the volume of liquid would be much smaller than that shown.
Similarly if the gas in that flask is condensed the volume of liquid would be much smaller than that shown.
Why is steam so hot???
You probably have never observed that freezing releases heat energy, but you will have observed that condensation of steam releases heat energy if you have ever stuck your hand into the steam above a pot of boiling water. The steam condenses on your hand and releases heat energy to give you a nasty burn.
How is evaporation different from boiling?
Water puddles disappear after it rains. This is not due to boiling but to evaporation. Evaporation occurs because the water at the surface of the puddle gets enough heat energy from the sun to vaporise. The vapour mixes with the air and is blown away by the wind.
There is actually some vapour (gas) above the surface of the liquid in the stoppered flask above. It the stopper were removed, the liquid would evaporate because the vapour can mix with the air.
Acknowledgement: Most of the questions in the next section of this module are from Yezierski, Ellen J.; Birk, James P. J. Chem. Educ. 2006, 83, 954.