Video Transcript
Given the information in the table,
which organic compound has the greatest vapor pressure at 25 degrees Celsius?
Vapor pressure is the pressure
exerted by a vapor above its liquid. Substances with weaker
intermolecular forces evaporate more readily. And this causes them to have a
relatively high vapor pressure value. Substances with strong
intermolecular forces will have lower vapor pressure.
We can also relate vapor pressure
to the volatility of a substance. Volatility describes how readily a
substance will evaporate. The more volatile a substance is,
the greater its vapor pressure is at a given temperature. Typically, a substance with high
volatility will have a low boiling point.
When thinking about the liquids in
the table, the liquid with the greatest vapor pressure is expected to have the
lowest boiling point. And the liquid with the lowest
vapor pressure would have the highest boiling point. In the table, we see that
methylpropane has the lowest boiling point. In fact, the boiling point of
methylpropane, also known as isobutane, is so low that it is a gas at 25 degrees
Celsius. However, it is often stored and
shipped as liquefied gas and exists as a liquid–gas mixture inside the
container. Methylpropane also has the weakest
intermolecular forces of all the liquids in the table and would be expected to have
the greatest vapor pressure.
Therefore, the organic compound
that has the greatest vapor pressure at 25 degrees Celsius is methylpropane.
