We have seen that as the temperature of a liquid is raised, its vapor pressure increases, what we observe, however, depends on whether the heating takes place in a closed or an open container
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at a certain temperature the vapor pressure becomes the same as the external pressure, at this temperature the vapor can expand indefinitely, moreover because there s no constraint on expansion bubbles of vapor can form throughout the body of the liquid the condition known as boiling
The pressure at which the vapor pressure of a liquid is equal to the external pressure is called the boiling temperature