VAPOUR PRESSURE
Is the pressure exerted by a vapor in thermodynamic equilibrium or it can also
be defined as the pressure exhibited by vapor present above a liquid surface
When two objects are in thermal dynamic, they are said to have the same
temperature. During the process of reaching thermal equilibrium, heat, which is
a form of energy, is transferred between objects. As the temperature of a liquid
increases the attractive interactions between liquid molecules become less
significant in comparison to the entropy of these molecules in the gas phase
increasing the vapor pressure thus liquids with strong intermolecular
interactions are likely to have smaller vapor pressure, with reserve true
It relates to the balance of particles escaping from a liquid or solid in equilibrium
with those coexisting vapor phase. A substance with high vapor pressure at
normal temperature is referred to as Volatile
Factors that influence vapor pressure
• Temperature
• Intermolecular forces of attraction
Increasing temperature causes more evaporation and increases the vapor
pressure because more liquid particles escape as gas
Intermolecular forces, Evaporation, Vapor Pressure and Boiling Point
Substances with strong intermolecular attractions will have low vapor
pressure due to low evaporation and high boiling point because a lot of energy is
needed to go from liquid to gas due to the strong attractions
Vapor Pressure and Boiling Point
Atmospheric pressure interferes with evaporation and thereby making it difficult
to boil thus therefore for a liquid to boil, vapor pressure of a liquid is equal to
the atmospheric pressure
Weak intermolecular attraction
Strong intermolecular attraction
Volatile liquids evaporate very easily
and have a high vapor pressure
Don’t evaporate easily and have low
vapor pressure
Have low boiling point
High boiling point
Bp ethanol
Bp water=°C
