I've been trying to find the difference between volatility and evaporation and I can see almost everywhere that the volatility is the tendency of a substance to vaporize. So Q1: what makes the volatility special? I understand that the fuels are generally volatile, and I understand that they vaporize faster than water, for example. But Q2: is this the only difference?

I was thinking that volatility also makes the vapor have a different chemical composition, or did I get it wrong?

For instance, the water (a non-volatile liquid) vapor is still $\ce{H2O}$, right? Q3: Will the vapor of benzene $\ce{C6H6}$ still be $\ce{C6H6}$ or it brakes into other compounds?

  • $\begingroup$ No it's still going to be benzene vapour. $\endgroup$ Commented Feb 23, 2017 at 18:41
  • $\begingroup$ Q2: Yeah vaporised water is still H2O but not H2O(aq), vaporised water is H2O(g). This is called change of state Q3: this is also true for the C6H6(g) $\endgroup$
    – creekorful
    Commented Feb 23, 2017 at 18:48
  • $\begingroup$ Thank you, both. So basically volatile substances are substances with low molecular forces and that's all, true? Nothing special with them when speaking about vaporization. Is this true? $\endgroup$
    – Physther
    Commented Feb 23, 2017 at 18:59

1 Answer 1


Evaporate is a phase change from liquid to gas without changing the molecule itself (or the atoms is the liquid is atomic).

Volatility is essentially the tendency of a liquid to evaporate. So a highly volatile liquid would show a great tendency to evaporate.

A measure of volatility is the vapor pressure. There is a very related term partial pressure. So if we think of air as being nitrogen and oxygen, then there is a partial pressure for nitrogen and a partial pressure for oxygen, and the sum of the two partial pressure is the actual pressure (the absolute pressure).

To make things a bit more confusing chemists think of absolute pressure. So because we are in earth's atmosphere there is always 1 atmosphere of gas pressure. So when you pump a car tire up to 30 lbs/sq inch, there is already 14.7 lbs /sq inch air pressure due to the atmosphere. So the absolute pressure inside the tire is 44.7 lbs/sq inch.


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