Water has a high heat of vaporization
The heat of vaporization of water is one of the highest of all liquids.
Scientific Explanation
To completely convert one liter of water at 100 degrees Celsius into steam requires about 2260 kilojoules — enough energy to heat the same liter of water from 0 to 540 degrees Celsius, if that were possible. This value is nearly three times higher than for ethanol (846 kJ/kg) and more than five times higher than for benzene (394 kJ/kg).
The cause lies in hydrogen bonds. During vaporization, every molecule must be pulled out of the liquid network, meaning all bonds to its neighbors must be broken simultaneously. Since each water molecule participates in up to four hydrogen bonds, each with a binding energy of about 20 kilojoules per mole, the total energy requirement is extraordinarily high.
For comparison, ethanol also forms hydrogen bonds, but only about two per molecule. Benzene has none at all — only weak dispersion forces hold its molecules together.
Step by Step
Adding Energy
We heat water starting at room temperature. The x-axis shows energy input in kilojoules per kilogram, the y-axis shows temperature in degrees Celsius.
Temperature Rises
Temperature climbs steadily from 20 to 100 degrees Celsius. Water needs 4.18 kJ/kg per degree -- already unusually high for a liquid.
The Plateau
At 100 degrees Celsius something remarkable happens: temperature stays constant even though energy keeps flowing in. All energy goes into the phase change -- liquid water becomes steam.
The Comparison
Water needs 2260 kJ/kg to vaporize -- nearly three times more than ethanol (840 kJ/kg) and over four times more than acetone (520 kJ/kg). The reason: each molecule must break up to four hydrogen bonds simultaneously.
Everyday Relevance
The high heat of vaporization is why sweating cools us: when sweat evaporates from the skin, it removes large amounts of heat from the body. Evaporating just a few milliliters is enough to noticeably lower the temperature. Wet clothing feels cold for the same reason — the evaporating water draws heat from the fabric and the skin.
In nature, the high heat of vaporization regulates climate: evaporation over the oceans transfers enormous amounts of energy into the atmosphere, which is released again during cloud formation and precipitation. This water cycle is one of the most important heat pumps on Earth.