Chem 1220: Lecture 2 Flashcards
(19 cards)
What is a solution?
A homogeneous mixture of two or more substances where one substance (solute) is dissolved in another (solvent)
What are the three types of solutions?
- Gaseous solutions
- Liquid solutions
- Solid solutions
What is entropy (S)?
A measure of disorder in a system. According to the 2nd law of thermodynamics, the universe tends towards disorder.
What two main factors determine if substances will form a solution?
- Natural tendency toward mixing (Entropy - ΔS)
- Intermolecular forces between solute & solvent molecules (Enthalpy - ΔH)
What is the equation for solution formation enthalpy?
ΔHsoln = ΔHsolute + ΔHsolvent + ΔHmix
What are the steps in the energetics of solution formation?
- Breaking solute-solute IMFs (positive ΔH)
- Breaking solvent-solvent IMFs (positive ΔH)
- Forming solute-solvent IMFs (negative ΔH)
Why does table salt (NaCl) dissolve in water?
Water molecules surround the Na+ and Cl- ions through ion-dipole forces, overcoming the ionic bonds in the crystal structure
What is Coulomb’s Law?
F = k(q₁q₂/r²) - describes the force between charged particles
What are immiscible liquids?
Liquids that DO NOT mix or form solutions with each other (example: water and oil)
What is saturation?
The point at which no more solute can dissolve in a solvent at a given temperature
What happens in a saturated solution at equilibrium?
There is constant movement back and forth between solid solute and dissolved solute, with the concentration remaining constant
What is the ‘like dissolves like’ rule?
Polar substances dissolve in polar solvents; nonpolar substances dissolve in nonpolar solvents
How does pressure affect gas solubility?
Increasing the partial pressure of a gas increases its solubility in a liquid (Henry’s Law)
What is Henry’s Law?
Sg = kPg (The solubility of a gas is directly proportional to its partial pressure above the solution)
How does temperature affect gas solubility?
Gas solubility decreases as temperature increases
How does temperature typically affect solid solubility?
Most solid solutes become more soluble as temperature increases (with some exceptions)
What is supersaturation?
A solution that contains more dissolved solute than is normally possible under given temperature conditions
What happens to molecular compounds when they dissolve?
The molecular units stay intact, and each neutral molecule is solvated by solvent molecules
What happens to ionic compounds when they dissolve?
The ionic bonds break and the ions become solvated (surrounded by solvent molecules)
