The melting and boiling point of water

Core Concept

In this tutorial, you will learn about the melting point, freezing point, and boiling point of water, and some important concepts.

What is water?

Water is a molecule consisting of three atoms, one oxygen atom and two hydrogen atoms. Due to a force called hydrogen bonding, water molecules adhere to one another. Water exists in a gaseous, liquid, and solid state depending on its temperature. On earth, water exists in all three states of matter: solid, liquid, and gas (sometimes called vapour).

Melting Point of water

Melting is a state change of a solid into a liquid when heat is applied. As the temperature rises, the molecules move faster. Once they have reached a specific temperature, they break free from their rigid crystalline structure and begin to move more freely, now in the liquid state. In a pure crystalline solid, this process occurs at a fixed temperature. The melting point of water is about 32 degrees Fahrenheit (0 degrees Celsius) for pure water at sea level (normal elevation). At other elevations the melting point will change due to different ambient pressure. These changes are discussed further in a section below.

IMages of ice cubes melting. Ice is a form of water melting

Boiling Point of water

Boiling is the process when a liquid changes states and turns into a gas. As temperature increases, a molecule will gain enough energy to become a gas, where intermolecular distances become much larger compared to the liquid state. The boiling point for water is 212 ºF or 100 ºC, whereas the boiling point of salt water is about 102 ºC. The boiling point of water will also change at non-standard pressures. Impurities in water, like salt, modify the intermolecular interactions between water molecules that result in a modified boiling point.

Boiling water in a pot
Boiling water in a pot (Source: Wikimedia Commons)

Boiling at High Elevations

The standard boiling temperature of water only applies at standard pressures, that is at sea level. As you move to higher elevations (lower pressure) the boiling temperature will decrease.

For example, although water normally boils at 100 oC (212 oF), on Mount Everest (elevation about 27,000 feet) water boils at 68 oC (154 oF).

Mount everest
Mount Everest. At camps for Mount Everest, water will boil at a lower temperature than boiling water at the beach (sea level). (Source: Wikimedia Commons)

What if we try to boil water deep in the ocean? In some of the deepest parts of the ocean, water will stay in its liquid state until a temperature of 400 oC (750 oF). Here the pressure is much higher than at normal sea level, and this makes it so more energy (higher temperature) is needed to boil the water.


Melting point-a temperature where a substance can change from its solid state to a liquid state.

Freezing point -the temperature at which a substance undergoes a phase change from a liquid state to a solid-state.

Boiling point– the temperature at which a liquid undergoes a phase change and turns into a vapor.

Fun Facts

  • Water in its solid form floats instead of sinking when sitting in liquid water. This is different from most other solids.
  • Gas can be turned into a liquid or even a solid through pressure.
  • The boiling point and freezing point can differ depending on how much salt is in water.
  • At higher altitudes, the boiling point of water is lower.

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