In which phase change or hydrogen bonds formed
Hydrogen bonds are formed when two molecules with a partial positive charge and a partial negative charge interact. This typically occurs when two molecules with hydrogen atoms, such as water, interact. Hydrogen bonds are not formed during a phase change.
Hydrogen bonds are formed during the phase change from a liquid to a solid, and also during the phase change from a liquid to a gas.
To understand why hydrogen bonds are formed during these phase changes, we need to consider the unique properties of hydrogen bonding. Hydrogen bonding occurs when a hydrogen atom is covalently bonded to an electronegative atom (such as nitrogen, oxygen, or fluorine) and experiences attraction to another electronegative atom nearby. This results in a relatively strong intermolecular force that holds molecules together.
In the case of the liquid-to-solid phase change (freezing), when a substance cools down, its particles slow down and come closer together. This proximity allows the hydrogen bonds to form between neighboring molecules, which helps to hold them in a more ordered, solid arrangement. This is why many solid substances, such as ice, have a crystalline structure.
Similarly, during the liquid-to-gas phase change (vaporization or boiling), when a substance is heated, its particles gain energy and start moving more rapidly. As the particles gain enough energy to overcome the intermolecular forces, they break away from one another and the liquid turns into a gas. However, even in the gaseous state, hydrogen bonds can still exist between molecules that have the necessary hydrogen and electronegative atoms. These hydrogen bonds contribute to the overall properties of the gas, such as its boiling point and heat of vaporization.
In summary, hydrogen bonds are formed during the phase changes from a liquid to a solid and from a liquid to a gas, due to the rearrangement and proximity of molecules during these transitions.