Atkins & de Paula:
Physical Chemistry for the Life Sciences
The distribution of molecular speeds depends on temperature and the molar mass of the molecules. Note that the most probable speed (corresponding to the peak of the distribution) increases with temperature and with decreasing molar mass and, simultaneously, the distribution becomes broader. The formula is
Where s is the speed (m s -1), M is the molar mass (g mol -1), T is the temperature (kelvin), and R is the gas constant. Note: The factor of 2000 in the formula includes a factor of 103 to convert from grams per mole to kilograms per mole.
To graph a distribution enter the parameters (e.g., M and T) and hit New Plot. Up to 5 plots can be
displayed at one time. The Clear button will remove all plots. To see the parameters for each plot hit the
Legend on/off button. The Redraw button will refresh the graph. This is useful when the function
domain (i.e., s ) has been changed. To see the value of each plot at a given point, move your cursor to the desired
location then click and hold.