Q:

Why does water have a high boiling point?

A:

Water has a high boiling point because its molecules are bound together by hydrogen bonding, which is a very strong intermolecular force. It takes more kinetic energy, or a higher temperature, to break the hydrogen bonding between water molecules, thus allowing them to escape as steam.

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Boiling of a liquid involves increasing the kinetic energy of the molecules by increasing the temperature of the liquid. As the molecules gain more kinetic energy, they are able to escape the intermolecular forces that hold them together as a liquid and become gaseous molecules. The amount of kinetic energy required to break the intermolecular forces increases with the strength of the intermolecular force involved. Stronger intermolecular forces require more energy to disrupt, thus resulting in a higher boiling point for that substance.

Water molecules are held together by hydrogen bonding, which is a very strong intermolecular force. Each water molecule is polar because the oxygen has a partial negative charge, while the hydrogen atoms have a partial positive charge. The partial negative charge of one water molecule exerts a strong attractive force over the partial positive charge of a different water molecule. In order to boil water, the molecules have to be supplied with a sufficient amount of kinetic energy to escape the strong hydrogen bonding between molecules. The temperature must be increased in order to increase the kinetic energy of the molecules. The presence of the hydrogen bonds thus elevates the boiling point of water.

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