Trouble understanding how volatility is measured

[Stellar1]

I'm having a bit of trouble understanding how volatility is measured. I understand the units of volatility are mg/m3, but I don't know how a measurement of concentration relates to how volatile a liquid is. Wouldn't the vapour concentration of the liquid depend on the amount of time that it was allowed to sit an evaporate?

 

[Borek]

Wouldn't the vapour concentration of the liquid depend on the amount of time that it was allowed to sit an evaporate?

No. Once the vapor gets saturated, its concentration doesn't change any further, no matter how long you wait.

If you take an empty bottle, add half an inch of water, close the bottle and leave it alone, no matter how long you wait there will be always the same amount of water resting at the bottom. That's because the vapor above is saturated. If you leave the bottle open, the water will eventually dry out, but that's because air is almost never saturated, plus it is exchanged, so the vapor can escape.

 

[Stellar1]

Yeah, so in that case the units would represent the saturation concentration... But saturation concentration would be achieved eventually regardless of liquid, would it not? How does this concentration tell me how fast a liquid will evaporate?

 

[Borek]

It doesn't.

Other than the obvious thing that the higher the saturated vapor pressure, the faster the evaporation.

Trick is, there are many things that have to be taken into account when trying to evaluate evaporation speed. Heat transfer and air movement being probably the most important ones (and already difficult to describe).

 

[LudusRex]

I can understand your confusion regarding the measurement of volatility. Volatility is a measure of a substance's tendency to evaporate or vaporize into the surrounding air. It is typically measured in units of mg/m3, which refers to the amount of substance (in milligrams) present in a given volume of air (in cubic meters).

The concentration of a volatile substance in the air is affected by various factors, such as temperature, pressure, and the surface area of the liquid. However, the amount of time the liquid is allowed to sit and evaporate does not directly impact the measurement of volatility. Instead, it affects the rate of evaporation, which can be accounted for when conducting experiments or making calculations.

To better understand how volatility is measured, it is important to consider the properties of the substance itself. Volatile substances have a high vapor pressure, meaning they have a strong tendency to escape the liquid phase and enter the gas phase. This results in a higher concentration of the substance in the air, leading to a higher measurement of volatility.

In summary, volatility is a measure of a substance's ability to evaporate into the surrounding air, and it is influenced by various factors. The measurement of volatility in units of mg/m3 reflects the concentration of the substance in the air and is not directly affected by the amount of time the liquid is allowed to sit and evaporate.