Partial Pressure vs. Vapor Pressure: Key Differences Explained
Partial pressure is the portion of total pressure exerted by any single gas in a mixture; vapor pressure is the pressure created by a substance’s own vapor when it’s in equilibrium with its liquid or solid phase.
People swap them because both terms end in “pressure” and involve gases above liquids. In daily life, you see vapor pressure when a sealed water bottle bulges on a hot day, while partial pressure explains why oxygen masks work at high altitude.
Key Differences
Partial pressure depends on how much of a gas is present and what else is in the mix; vapor pressure depends only on the substance’s identity and temperature. One changes if you add or remove another gas, the other stays the same until the temperature shifts.
Examples and Daily Life
Pop a soda can: the hiss is mostly CO₂’s partial pressure escaping. Leave that same soda open; its vapor pressure lets water slowly evaporate until the drink goes flat.
Can two gases have the same partial and vapor pressure?
Yes, but only by coincidence and under very specific conditions, not in typical situations.
Does vapor pressure apply to solids too?
Absolutely. Ice and mothballs also exert vapor pressure, just usually much lower than liquids.