Jan 28

Key Concepts in Solutions and Equilibria

Clausius-Clapeyron Equation

• Purpose: Used for calculating vapor pressure and temperature relationships.

• Formulations:

  • Graphing: Natural log of vapor pressure vs. inverse temperature yields a linear graph.

    • Slope: -ΔH/R (where ΔH is enthalpy change, R is universal gas constant)

    • Y-Intercept: ln(β)

  • Two-Point Form: Requires two data points along with Δ vaporization.

Heating Curves

• Basic Equation: q = mcΔT (heating or cooling substances)

  • Where: q = heat added, m = mass, c = specific heat, ΔT = temperature change.

• Phase Change Equation: q = n × ΔH (for phase changes such as vaporization)

  • Where: n = number of moles, ΔH = enthalpy change.

Crystal Structures

• Unit Cells: Focus on three types: Primitive, Face Centered, and Body Centered.

  • Calculations Required: Number of atoms in unit cell, relationship between radius (r) and unit cell length (l).

  • Coordination Number: Discussed in lab, indicates how many nearest neighbors surround an atom.

  • Percent Occupied Volume: To be calculated based on the unit cell configurations.

Solutions and Their Characteristics

Types of Solutions

• Homogeneous Saturated Solution: Even concentration throughout the substance, maximum solute dissolved.

• Heterogeneous Saturated Solution: Contains undissolved solute, not a true solution.

  • Example: Maximum solubility with some undissolved material present.

Supersaturated Solutions

• Definition: More solute dissolved than the solubility limit at a given temperature.

• Formation: Involves heating the solution to dissolve excess solute, cooling results in supersaturation.

Entropy and Enthalpy in Solutions

• Endothermic Reactions: An increase in temperature leads to more hydration (dissolving).

• Exothermic Reactions: Decrease in temperature leads to crystallization; thus, heat is released.

Chemistry of Ionic Compounds in Solutions

Solubility Principles

• Like Dissolves Like: Polar solutes generally dissolve in polar solvents (e.g., ethanol and water).

• Intermolecular Forces: Various forces such as hydrogen bonding, ion-dipole interactions play a crucial role in solubility.

  • Example: Ammonium chloride dissolves due to ion-dipole forces; silver chloride does not due to solubility rules.

Solubility Curves

• Base Calculations: Provided temperatures and solubility data for various salts (e.g., potassium nitrate) are essential for predicting behavior at different conditions.

Understanding Concentration Units

Molarity and Molality

• Molarity (M): Moles of solute per liter of solution.

• Molality (m): Moles of solute per kilogram of solvent.

• Temperature Dependence: Molarity changes with temperature due to volume changes; molality remains constant.

Mole Fraction and Percent Concentrations

• Mole Fraction: Moles of one component divided by total moles; it's a ratio that helps in calculations involving properties of components.

• Percentage Concentrations: Calculated in terms of weight/weight, volume/volume, and weight/volume.

Special Cases of Concentration Units

• Weight Percent: Grams of solute in 100 grams solution.

• Parts Per Million (PPM) and Parts Per Billion (PPB): Used for expressing concentration of contaminants in water/air.

Important Notes for Exam Preparation

• Chemistry Calculations: Familiarize with molar mass conversions, density for solution calculations, and how pressures relate to gas solubility (Henry's Law).

• Understand Graphs and Equations: Be able to interpret graphs of solubility vs temperature and apply relevant equations appropriately.

• Functional Groups: Identify basic functional groups including alcohols, amines, carboxylic acids, and esters with chemical structures.