The breaking of these bonds is caused by the motion (kineticenergy) of the water molecules due to the heat contained in the system.
When the heat is raised as water is boiled, the higher kineticenergy of the water molecules causes the hydrogen bonds to break completely and allows water molecules to escape into the air as gas (steam or water vapor).
On the other hand, when the temperature of water is reduced and water freezes, the water molecules form a crystalline structure maintained by hydrogen bonding (there is not enough energy to break the hydrogen bonds).
With most other liquids, solidification when the temperature drops includes the lowering of kineticenergy between molecules, allowing them to pack even more tightly than in liquid form and giving the solid a greater density than the liquid.
As a result of the network of hydrogen bonding present between water molecules, a high input of energy is required to transform one gram of liquid water into water vapor, an energy requirement called the heat of vaporization.
A considerable amount of heat energy (586 calories) is required to accomplish this change in water.
Eventually, as water reaches its boiling point of 100° Celsius (212° Fahrenheit), the heat is able to break the hydrogen bonds between the water molecules, and the kineticenergy (motion) between the water molecules allows them to escape from the liquid as a gas.
The fact that hydrogen bonds need to be broken for water to evaporate means that a substantial amount of energy is used in the process.
As the water evaporates, energy is taken up by the process, cooling the environment where the evaporation is taking place.
Evaporation of water requires a substantial amount of energy due to the high heat of vaporization of water.
While this process still consumes ATP to generate that gradient, the energy is not directly used to move the molecule across the membrane, hence it is known as secondary active transport.
This secondary process is also used to store high-energy hydrogen ions in the mitochondria of plant and animal cells for the production of ATP.
The potential energy that accumulates in the stored hydrogen ions is translated into kineticenergy as the ions surge through the channel protein ATP synthase, and that energy is used to convert ADP into ATP.
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