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.

Why is water important?

Water is one of the most plentiful compounds that is also very essential. It is tasteless, odorless, in small quantities even appear colorless but has a slight blue color. Water is very important to the earth and to life.

Image of a water droplet, after the melting point of water

States of Water

 On a day-to-day basis, one can encounter water in three states of matter as a solid, liquid, and gas. When water is in its solid form, it does not change shape or volume due to the atoms being in a fixed position contingent on one another. When water is in its liquid form, it can change shape to fill the space it currently occupies. The atoms that make up water are not rigid but move freely around the liquid. Finally, when water is in its gaseous state, it is referred to as steam or vapor.

Melting Point of water

Melting is change of a solid into a liquid when heat is applied. As temperature rises, the energy in molecules increases leading to the molecules moving faster. Once they have reached a specific temperature, they break free from their rigid structure and begin to move more freely. In a pure crystalline solid, this process occurs at a fixed temperature. This is known as the change from a solid-state of matter to a liquid state of matter. 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 pressures from the atmosphere. 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 when a liquid changes states and turns into a gas. As temperature increases, a molecule will gain enough energy to become a gas. The boiling point for water is 100 degrees C (212 degrees F), whereas the boiling point of salt water is about 102º Celsius. The boiling point of water will also change at non-standard pressures.

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

The freezing point of water

Water freezes at 32 degrees Fahrenheit (0 degrees Celsius), whereas saltwater freezes at about 28.4 Fahrenheit ( -1.8º Celsius). Freezing is when water goes from the liquid phase to the solid phase.

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 100oC (212oF), on Mount Everest (elevation about 27,000 feet) water boils at 68oC (154oF). That is a dramatic difference. Sometimes you also see an example of this in baking. At higher elevations, food has to be cooked for longer and ratios of ingredients may change slightly.

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 400oC (750oF). 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 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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