Q:

Why does water have a high boiling point?

A:

Quick Answer

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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Full Answer

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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Related Questions

  • Q:

    What type of bonding holds two or more water molecules together?

    A:

    The type of bonding that holds two or more water molecules together is called hydrogen bonding. Water molecules are polar, meaning they have slightly negative and positive regions within the molecule.

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  • Q:

    Why does ice have a lower density than water?

    A:

    The hydrogen bonding gives water a structure with considerable space between the molecules, making it expand in size and become less dense in a solid state than in a liquid one. Because water is denser than ice, ice cubes float on the surface of water. Hydrogen bonds link each water molecule to an average of 3.4 other water molecules, and the lattice that forms when water freezes has a lot of empty space inside it.

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  • Q:

    Why does water have a high heat capacity?

    A:

    Water has a high heat capacity because a lot of heat energy is required to break the hydrogen bonds found in a molecule of water. Because the majority of heat energy is concentrated on breaking the hydrogen bonds, the water molecule itself heats up after the bonds are broken.

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  • Q:

    Why does salt make water boil faster?

    A:

    Adding salt to water actually boosts the boiling point a few degrees, but even with the higher boiling point, salt water boils faster than pure water because salt water has a lower heat capacity than pure water. This means that it does not take as much energy to boost the temperature of salt water as it does to heat up pure water.

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