CHMA11H3 Lecture 2: CHMA11 Lecture 2

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CHMA11 Lecture 2: Solutions
- Solution: a homogenous mixture of two or more substances or components
o Made up of 2 main components, the solute and the solvent
Solvent: the majority component in which the solute is dissolved in
Solute: the minority component that dissolves in the solvent
o Substances will tend to combine into uniform mixtures unless it is highly
unfavourable energetically
Tend not to separate into pure substances
There is a natural tendency towards mixing that yields solutions of
uniform concentration
o Aqueous Solutions: solutions in which water is the solvent and a solid, liquid or
gas is the solute
Eg: salt water is a common example of an aqueous solution
o Solvents are distinct in terms of the solutes they are able to dissolve within
themselves
A particular solvent will not dissolve all possible solutes
Solubility: refers to the amount of a substance that will dissolve in a
given amount of solvent
The solubility of one substance in another depends on two things
o Nature’s tendency toward mixing
o Intermolecular forces
- Entropy: nature’s tendency toward mixing
o The formation of a solution does not always lower the potential energy of its
component molecules
Phenomenon is best seen in the formation of a homogenous solution of
two ideal gases
When a barrier is removed allowing the gases to interact, they will
mix but their potential energies will remain the same
The tendency to mix is thus not to reduce potential energy but
instead is related to the concept of entropy
o Entropy: measure of energy randomization or dispersal in a given system
Concerned with the pervasive tendency for energy to spread out and
disperse
- Intermolecular forces and solubility
o Solids and liquids exhibit a range of different intermolecular forces
Dispersion forces, dipole dipole forces and hydrogen bonds
These forces can either promote solution formation or prevent it
Depends on the nature of the forces in the given combination of
solute and solvent
o There are 3 key intermolecular force interactions that dictate solution formation
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