The boiling point of gases is the temperature above which a gas will transform from liquid into a gaseous state upon heating. This happens because the heat energy applied to the liquid causes its molecules to spread out, reducing the force of intermolecular interactions, which is what gives the liquid its shape.
The higher the vapor pressure of a liquid, the lower its normal boiling point will be. This is because the more a liquid’s molecules spread out, the easier it is for them to reach the air molecules above them and interact with them. A liquid’s vapor pressure also depends on the nature of its molecules and its structure. For example, simple carboxylic acids dimerize by forming hydrogen bonds in the liquid state which raises their normal boiling points, whereas aromatic compounds have much lower boiling points because they form more compact bonds.
If you heat a substance above its boiling point, it will continue to rise until the vapor pressure equals the atmospheric pressure, at which point it will begin to boil. This is known as its critical point. At the critical point, the liquid and vapor phases merge into a superheated gas.
Several factors influence the boiling point of a liquid, including its temperature and its purity. In particular, the presence of dissolved solids causes the boiling point to be lower. For example, water can only boil at temperatures above 100°C when it is pure. In addition, the atmosphere’s pressure decreases as you increase your elevation, so a liquid will boil at a lower temperature at high altitudes.