At any set temperature, the individual molecules in any bulk sample (any sample observable by eye) have a variety of energies. While some have low kinetic energy, others have relatively high kinetic energy. The distribution of the velocities, and therefore energies, is referred to as a Boltzmann distribution, named after Ludwig Boltzmann, an Australian mathematician and physicist who worked largely in part on the kinetic theory of gases. A plot of the number of molecules with any particular energy vs. the molecular energy is called a Boltzmann plot.
Molecules in a liquid are held together by forces called intermolecular forces. Because of the distribution of energies for molecules in a sample, only a fraction have enough energy to overcome their intermolecular forces and escape from the liquid to the vapor (gas) phase. The fraction of molecules that can escape into the vapor phase depends both on the energies of the molecules and the strength of the intermolecular forces that hold them together.
This module illustrates the kinetic energy distribution of molecules in the liquid phase, creating plots of the relative number of molecules vs. molecular energy, which gives an indication of the ability of those molecules to escape the liquid phase and enter the gas phase.
INSTRUCTIONS
1. Select the intermolecular force strength by clicking on
one of the IMF strength option buttons.
2. Select a temperature by adjusting the Temperature scroll
bar, which adjusts the temperature between 200. and 500. K.
3. Click on the Calculate button to generate the distribution plot.
Multiple plots may be put on the screen at any time and the Clear Plot button clears the plot area. When an IMF strength is chosen, a vertical line appears to indicate the amount of energy a molecule requires to be capable of escaping into the gas phase. All molecules with less than this amount of energy (to the left of the line) can not break the forces between itself and its neighbors, and therefore must remain in the liquid phase.
