The temperature at which a subtance changes from liquid to gas. Boiling point is the same temperature as condensation point.

The temperature at which a given liquid boils. It is the temperature at which the vapor pressure of a specified liquid equals the atmospheric pressure.

To pass from liquid to gas a substance needs heat added to it to change the temperature, plus an additional amount called the latent heat of vaporization.

Commonly abbreviated B.P. or b.p.

The boiling point of a solution is in general higher than that of the pure solvent. The extra temperature is called the boiling point elevation. Each solvent has a constant called the boiling point elevation constant, symbol kb. The constant for water is 0.52 K kg mol-1.

The increase in boiling point is not affected by what solute is dissolved in the solvent, only by what amount (in moles) of solute is present. (This is called a colligative property.) The formula is

ΔTb = kb · m

where m is the molality (concentration in molals, or moles per kilogram). These are not the same as the elevation constants.

Note that one mole of NaCl placed in solution is two moles, one each of Na+ and Cl-. It is the number of ions that counts.

Similarly the presence of ions in solution takes a freezing point depression from a pure freezing point.

Here are some boiling points in °C and their elevation constants for common solutes:

water          100.0      0.51
acetic acid    118.5      2.5
benzene         80.15     2.58
chloroform      60.19     3.66
ethanol         78.26     1.22
ether           34.60     2.11
nitrobenzene   210.9      5.01
Note that the boiling point of water is no longer exactly 100°C, since the Celsius and absolute scales have been redefined in terms of the triple point of water.

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