Role of Probability and Particle Dispersion in Solubility and Solution Dynamics, Schemes and Mind Maps of Dynamics

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Chapter 15

Solution Dynamics

An Introduction to Chemistry

by Mark Bishop

Chapter

Map

Why Changes Happen

• Probability helps us to predict that the system will shift to state B if state B has its particles and energy more dispersed, leading to more ways to arrange the particles and energy in the system.

9 - Point

Universe

General

Statement

• Changes tend to take place to shift

from less probable, less dispersed

arrangements that have fewer

ways to arrange the particles to

more probable, more dispersed

states that have more ways to

arrange the particles.

Solids shift

spontaneously to gases.

• Why does dry ice, CO 2 (s) , spontaneously shift to CO 2 (g)? - Internal kinetic energy is associated with the random movement of particles in a system. - Internal kinetic energy makes it possible for CO 2 molecules to move back and forth between solid and gas. - If the particles can move freely back and forth between solid and gas, they are more likely to be found in the more dispersed gas state, which has more equivalent ways to arrange the particles.

Gases Expand to Fill Container

When the barrier between the two chambers in the container shown in (a) is raised, it is possible that the gas will end up in one chamber, like in (b), but it is much more likely that it will expand to fill the total volume available to it, like in (c).

Particles tend to

disperse (spread out).

Gas in one chamber ® Gas in both chambers Fewer ways to More ways to arrange particles arrange particles Less probable More probable Less dispersed More dispersed

Ethanol and Water Mixing

Attractions Broken and Made

“Like Dissolves

Like”

• Polar substances are expected to

dissolve in polar solvents.

• For example, ionic compounds, which are very polar, are often soluble in the polar solvent water.
• Nonpolar substances are expected to

dissolve in nonpolar solvents.

• For example, nonpolar molecular substances are expected to dissolve in hexane, a common nonpolar solvent.

“Like Does Not

Dissolve Unlike”

• Nonpolar substances are not

expected to dissolve to a significant

degree in polar solvents.

• For example, nonpolar molecular substances are expected to be insoluble in water.
• Polar substances are not expected to

dissolve to a significant degree in

nonpolar solvents.

• For example, ionic compounds are insoluble in hexane.

Water

Solubility

• We call polar molecules or polar sections of molecules hydrophilic.
• We call nonpolar molecules or nonpolar sections of molecules hydrophobic.
• If we are comparing the water solubility of two similar molecules, the one with the higher percentage of the molecule that is polar ( hydrophilic ) is expected to have higher water solubility.
• We predict that the molecule with the higher percentage of its structure that is nonpolar ( hydrophobic ) to be less soluble in water.

Hydrophobic and Hydrophilic