The Clausius-Clapeyron equation is about phase changes between liquid and vapor, and tells you how pressure and temperature affect how easily a substance evaporates or condenses.
It relates the change in pressure of a substance to the change in temperature during a phase transition, like liquid to gas or the other way round:
where is the vapor pressure, is the temperature, is the universal gas constant, and is the enthalpy of vaporization (the energy required for the liquid to turn into gas). This shows that as temperature increases, so does the vapor pressure, meaning the liquid will turn into gas more easily.
This matters well beyond boiling water. It’s important for understanding weather patterns, calculating the boiling and freezing points of substances, and explaining how things like clouds and storms develop. For example, when you climb a mountain, the air pressure drops, and the boiling point of water also decreases (because pressure affects how easily molecules can escape the liquid). This equation can help calculate exactly how much the boiling point will change as you gain altitude.