How can the boiling point of a liquid be decreased?

The boiling point of a liquid can be decreased by decreasing the pressure exerted on its surface. This principle is grounded in the relationship between pressure and boiling point, commonly described by the notion that boiling occurs when a liquid's vapor pressure equals the atmospheric pressure above it. When the atmospheric pressure is reduced, the vapor pressure required for the liquid to boil is also lower, thereby allowing the liquid to reach its boiling point at a lower temperature.

For instance, this is why water boils at lower temperatures at higher altitudes, where atmospheric pressure is decreased. Techniques such as using a vacuum can effectively lower pressure and facilitate boiling at temperatures that are much lower than standard atmospheric conditions.

In contrast, dissolving a solid substance like salt in a liquid generally raises the boiling point due to a phenomenon known as boiling point elevation, which occurs because the solute disrupts the formation of vapor above the liquid. Increasing the pressure on the surface of the liquid will raise the boiling point, as it requires a higher temperature for the vapor pressure to match the higher external pressure. Finally, merely changing the temperature of the liquid by itself does not affect the boiling point unless it is specifically addressing pressure conditions accompanying that temperature change.