Boiling point

The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.

The boiling point of a liquid varies depending upon the surrounding environmental pressure. A liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. For example, water boils at 100 °C (212 °F) at sea level, but at 93.4 °C (200.1 °F) at 1,905 meters (6,250 ft)  altitude. For a given pressure, different liquids will boil at different temperatures

Microscopic view:

  • As a liquid is heated, its vapor pressure increases until the vapor pressure equals the pressure of the gas above it.
  • Bubbles of vaporized liquid (i.e., gas) form within the bulk liquid and then rise to the surface where they burst and release the gas. (At the boiling temperature the vapor inside a bubble has enough pressure to keep the bubble from collapsing.)
  • In order to form vapor, the molecules of the liquid must overcome the forces of attraction between them.
  • The temperature of a boiling liquid remains constant, even when more heat is added.

The boiling point of a liquid is the temperature at which its vapor pressure is equal to the pressure of the gas above it.The normal boiling point of a liquid is the temperature at which its vapor pressure is equal to one atmosphere (760 torr).

Factors Affect Boiling Point:

Pressure: when the external pressure is:

  • less than one atmosphere, the boiling point of the liquid is lower than its normal boiling point.
  • equal to one atmosphere, the boiling point of a liquid is called the normal boiling point.
  • greater than one atmosphere, the boiling point of the liquid is greater than its normal boiling point.

The following graph shows the boiling point for water as a function of the external pressure. The line on the graph shows the normal boiling point for water.

Substance
Boiling Point
Freezing/Melting Point
Aluminium
2,519
660.3
Argon
-185.8
-189.34
Butane
-1
-140
Calcium
1,484
842
Carbon
4,827
3,550
Carbon Dioxide
-57
-78
Chloroform
61.2
-63.5
Chlorine
-34
-101.5
Cobalt
2,870
1,495
Copper
2,562
1,085
E to M
Substance
Boiling Point
Freezing/Melting Point
Ethanol (Alcohol)
78.4
-114
Gold
2,856
1,064
Glycerol
290
17.8
Helium
-268.9
-272.2
Hydrogen
-252.9
-259.1
Iodine
184.3
113.7
Iron
2,862
1,538
Lead
1,750
327.5
Magnesium
1,091
650
Mercury
356.7
-38.8
Methanol
64.7
-97.6
N to P
Substance
Boiling Point
Freezing/Melting Point
Neon
-246
-248.6
Nickel
2,913
1,455
Nitric Acid
83
-42
Nitrogen
-195.8
-210
Oxygen
-183
-218.8
Phosphorus
280.5
44.2
Platinum
3,825
1,768
Plutonium
3,232
639.4
Potassium
758.8
63.4
Propane
-42
-188


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I am scientist is a result of small effort to make huge impact on children. To stimulate the curiosity of young scientist towards science. Each idea will start with a experiment followed by reasoning the result , scientific learning, vocabulary (recap the big words used), useful reference website and books, along with free downloadable worksheets.

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