Chem ch14,15,10

1. Colligative Properties
   Definition: Properties of solutions that depend on the number of solute particles, not their identity.

Types:

• Vapor pressure lowering $<br>ightarrow$ fewer solvent particles escape into gas phase.

• Boiling point elevation $<br>ightarrow$ solution boils at a higher temp than pure solvent.

• Freezing point depression $<br>ightarrow$ solution freezes at a lower temp than pure solvent.

Equations:

• $\Delta T<em>b = i \times K</em>b \times m$

• $\Delta T<em>f = i \times K</em>f \times m$

• $i$ = number of particles ($NaCl \rightarrow 2$, $CaCl_2 \rightarrow 3$, molecules $<br>ightarrow 1$).

1. Solution Concentration

• Percent by mass = $\left( \frac{\text{mass solute}}{\text{mass solution}} \right) \times 100$

• Percent by volume = $\left( \frac{\text{volume solute}}{\text{volume solution}} \right) \times 100$

• Molarity (M) = $\frac{\text{moles solute}}{\text{liters solution}}$

• Molality (m) = $\frac{\text{moles solute}}{\text{kilograms solvent}}$

• Dilution formula: $M<em>1V</em>1 = M<em>2V</em>2$

1. Solubility
   Solubility curves:

• On the line = saturated

• Above = supersaturated

• Below = unsaturated

Factors affecting solubility:

• Solids $\rightarrow \uparrow$ temperature $= \uparrow$ solubility

• Gases $\rightarrow \uparrow$ temperature $= \downarrow$ solubility; $\uparrow$ pressure $= \uparrow$ solubility (Henry’s Law).

• “Like dissolves like”: Polar dissolves in polar, nonpolar dissolves in nonpolar.

1. Intermolecular Forces
   Types:

• London dispersion (weak, temporary dipoles, nonpolar molecules).

• Dipole-dipole (polar molecules).

• Hydrogen bonding (H with N, O, F — strongest).

Effects:

• Stronger forces $\rightarrow$ higher boiling point, higher surface tension, lower vapor pressure.

1. Energy & Heat
   Energy types:

• Potential (position)

• Kinetic (motion).

Law of Conservation: Energy cannot be created or destroyed.

Phase changes:

• Endothermic (absorbs energy): melting, vaporization, sublimation.

• Exothermic (releases energy): freezing, condensation, deposition.

Specific heat formula: $Q = s \times m \times \Delta T$
Hess’s Law: $\Delta H$ is the same whether reaction occurs in one step or multiple.

🔑 Quick Memory Triggers

• Salt on icy roads $\rightarrow$ freezing point depression.

• Salt in boiling water $\rightarrow$ raises boiling point (doesn’t make it boil faster).

• $M<em>1V</em>1 = M<em>2V</em>2 \rightarrow$ dilution shortcut.

• Like dissolves like $\rightarrow$ polar with polar, nonpolar with nonpolar.

• Hydrogen bonding $\rightarrow$ explains water’s high boiling point and ice being less dense than liquid water.

❓ Practice Questions

• What happens to vapor pressure when solute is added?

• Calculate $\Delta T<em>f$ for $0.16 \ m \ CaCl</em>2$ ($i = 3$, $K_f = 1.86 \ °C/m$).

• Which solution is more concentrated: $3 \ g \ NaCl$ in $100 \ g$ water or $3 \ g \ NaCl$ in $400 \ g$ water?

• Why does water have a higher boiling point than ammonia?

• Endothermic vs exothermic: melting vs freezing.