15. Depletion Forces Flashcards
What is the depletion force? (entropy definition)
An effective attractive force that arises between large colloidal particles that are suspended in a dilute solution of small particles, due to an increase in entropy.
What is the depletion force? (osmotic pressure definition)
An osmotic pressure difference acting on two large colloidal particles due to the different concentrations of small particles in between and outside of them.
What is excluded volume?
The volume around a larger object in solution that cannot be entered by small particles. This volume is larger than the physical volume of the large object.
How does the excluded volume relate to the size of the small particles?
The centre of each small particle cannot enter the excluded volume, hence, it must be at least as big as the radius of the particles.
What happens to the excluded volume when two large objects approach one another?
The excluded volumes overlap so the total excluded volume decreases and the volume available to small particles increases.
What happens to the entropy of a system as excluded volume decreases?
The entropy increases
Define entropy
A measure of the number of possible microstates, consistent with the current macrostate.
Give the equation for energy change due to osmotic pressure
∆U = energy change
P_osm = osmotic pressure
∆V_excl = change in excluded volume
Define osmotic pressure
The pressure that arises from differences in concentration.
