Module 6: Phase Changes, Water and Solutions

Key Concepts in Module 6: Phase Changes and Water

• Phase Changes:

  • Heating and cooling curves illustrate changes in state with temperature.

  • Heat of Fusion and Heat of Vaporization are key concepts:

  • For water, these values are significantly higher than for other covalent substances due to strong hydrogen bonding.

• Kinetic Theory of Matter:

  • Solids:

  1. Particles are closely packed and vibrate in place.

  2. Fixed volume and shape;

  3. Melting point defines the transition to liquid.

  • Liquids:

  1. Particles are close together but not in fixed positions.

  2. Fixed volume but variable shape.

  3. Vapor pressure refers to the pressure of molecules escaping to gas phase.

  4. Boiling point is the temperature when vapor pressure equals atmospheric pressure.

Intermolecular Forces

• Types of forces:

  1. Dispersion Forces: Present in non-polar molecules (e.g., He).

  2. Dipole-Dipole Forces: Occur in polar molecules (e.g., HCl).

  3. Ion-Dipole Forces: Between ions and polar molecules (e.g., Na+ and H2O).

  4. Hydrogen Bonds: Strong forces between H and highly electronegative atoms (e.g., F, O, N).

Water Properties

• Covalent Bonding:

  • Strong intra-molecular forces result in unique properties of water.

• Key Characteristics of Water:

  • Highest density at 4 °C.

  • High heat capacity (4,186 J/kg°C), stabilizing temperatures in environments.

  • Universal solvent due to its polarity.

Solutions

• Definition: A solution forms when a solute dissolves in a solvent.

• Types of Solutions:

  • Saturated: Maximum solute dissolved at a given temperature.

  • Unsaturated: Less solute than the saturation point.

  • Supersaturated: More solute than possible at given conditions.

Ionic Equations and Reactions

• Writing Ionic Equations:

  • Strong electrolytes are shown in ionic form; weak electrolytes are written in their molecular form.

  • Example:

  • Molecular: Na2CO3 (aq) + 2HCl(aq) → CO2(g) + H2O(l) + 2NaCl(aq)

  • Ionic: CO3²⁻(aq) + 2H⁺(aq) → CO2(g) + H2O(l)

Solubility Rules and Concentrations

• Salinity: Measurement of total dissolved salts.

  • Freshwater < 500 mg/L; seawater ~ 35,000 mg/L.

• Concentration Units:

  • g/L, ppm, mol/L (M)

• Calculations:

  • Using concentration formulas: n = cV or c = n/V.

Final Points

• Prepare using provided feedback quizzes and relevant textbook chapters.

• Familiarize yourself with solving ionic equations and understanding solution behaviors under different conditions.