[metallica00789]

Hi everyone
Last week in the chemistry lab, we did an experiment to calculate the the change of temperature when different compounds evaporate. Surprisingly to me, 1-butanol caused a more change in temperature than ethanol. I expected that ethanol will cause more change in temperature because it has a stronger dipole-dipole forces between it's molecules compared to 1-butanol. I know that that 1-butanol is a longer chain so it has a stronger dispersion forces between it's molecules. Is that the cause for my observation?? 

[Vidya]

see if you check
butanol has higher the boiling point than ethanol.
now reason is stronger dispersion forces and presence of H bonding
however in ethanol  dispersion forces are very weak and  H bonding is the same extent as of the butanol

[metallica00789]

Thank you for your response.
Another point that I have not found an explanation to is the change in temperature caused ethanol and 1-propanol.
when the ethanol evaporated, it caused change in temperature by 9.69 °C. while 1-propanol caused change in temperature by 5.98 °C when evaporated.
Theoretically, 1-propanol should cause more temperature change because it has a stronger intermolecular due to the stronger dispersion forces!
I dont know if my date is wrong or there is a factor that I did not consider in my analysis.

[jusy1]

Hi,

I think to explain that we have to think about not only about the energy lost by the surrounding medium when one molecule evaporates but also on the number of molecules that evaporate. As ethanol is more volatile due to weaker intermolecular forces, the vapor pressure in equilibrium with the liquid will also be higher and that may overcome the fact that more energy is necessary to break the forces between higher alkanes as 1-propanol.