What Will Affect the Boiling Point of a Liquid?

Environmental Pressure

• The environmental pressure is one of the most essential factors affecting the boiling point of a substance. Environmental pressure is the pressure of the air immediately outside of or directly surrounding the substance. The normal boiling point of any substance is its boiling point at sea level, which is the first level of atmospheric or environmental pressure. Any changes in the environmental pressure will result in a directly proportional change in the boiling point of the substance (i.e., a rise in environmental pressure equals a rise in boiling point and a drop in environmental pressure equals a drop in boiling point). For example, a pressure cooker cooks food rapidly because it changes the environmental pressure surrounding the food and the liquid it cooks in.

Molecular Structure

• Another factor that affects boiling point is the molecular structure of the substance. The stronger and more complex the bonds holding the molecules of the substance together, the higher the boiling point of the substance, and vice versa. Generally, substances with stronger molecular bonds are heavier and more dense than substances with weaker bonds. For example, the gaseous element helium has the lowest boiling point of all elements at 4.22 degrees Kelvin (-268.93 degrees Celsius, -452.07 degrees Fahrenheit). Helium also has the second simplest molecular structure of any element, after hydrogen. Heavy metals, such as tungsten, have an incredibly strong molecular structure and therefore boil at over 5,000 degrees Kelvin (4,727 degrees Celsius, 8,540.6 degrees Fahrenheit).

Solute Concentration

• A solution is the result of one substance (the solute) being dissolved into another substance (the solvent). If a substance has other substances dissolved in it, the boiling point of the solvent will be altered higher or lower, depending on the solute. For example, salt has a much higher boiling point than water. So, when salt is dissolved in water, it will raise the boiling point of the water. The more salt in the water, the higher the boiling point.

Elevation

• Lastly, elevation affects a substance's boiling point. This is closely related to the factor of environmental pressure. As elevation increases, environmental pressure decreases, therefore the boiling point of a substance decreases as elevation increases. This is why packaged food items often have different cooking directions for high-altitudes.