Lecture Notes: Chemical Systems and Reactions

Introduction

• Continued discussion on basic concepts of chemical systems.
• Updated reading assignments in Chapter 2, excluding some content not relevant for exams or homework.

Recap of Previous Class

• Basic Properties of Elements/Molecules:
  • Atomic number, mass number, and atomic weight.
  • Importance of isotopes in determining atomic weight.
• Chemical Bonds:
  • Ionic bonds (difference in electronegativity ≥ 1.5)
  • Covalent bonds (difference in electronegativity ≤ 1.4)
• Types of Chemical Reactions in Environmental Engineering:
  • Precipitation dissolution (e.g., water softening)
  • Acid-base reactions (e.g., pH adjustment in water treatment)
  • Oxidation-reduction reactions (e.g., removal of organics in wastewater)
• Balancing Chemical Equations: Importance in determining reaction stoichiometry and engineering applications.

Detailed Topics

Water Softening and Chemical Reactions

• Precipitation Dissolution Reaction:
  • Removal of calcium ions through reactions with hydroxide ions and formation of sediments.
  • Example: Reaction between bicarbonate ion and hydroxide ion to form water and carbonate ion.

Complex Reactions and Balancing

• Balancing equations involves counting number of atoms on each side.
• Example reactions:
  • Iron oxidation and formation of iron oxide.
  • Barium chloride and sodium sulfate reaction forming barium sulfate and sodium chloride.

Chemical Equilibrium

• Equilibrium Constant (K): Determines the final state where reactants and products coexist.
• Calculating concentrations using equilibrium constant.
• Applications:
  • Solubility product
  • Acid-base equilibrium
  • Gas-liquid equilibrium

Solubility Product

• Dissolution of Solids in Water:
  • Example: Calcium carbonate and aluminum hydroxide.
  • Use of Ksp (solubility product) to determine ion concentrations.

Acid-Base Equilibrium

• Dissolution of acids into hydrogen ions and anions.
• Equilibrium Constant (Ka):
  • Strong acids (low pKa, e.g., hydrochloric acid).
  • Weak acids (high pKa, e.g., carbonic acid).
• Application in water systems and pH calculation.

Molarity and Chemical Concentrations

• Molarity (M): Concentration of species in water (moles per liter).
  • Examples with sodium chloride solution.

Chemical Equilibrium in Environmental Engineering

• Importance in designing water treatment and pollution control systems.

Other Important Concepts

• Moles and Molar Weight:
  • Definition and importance of isotopes.
  • Molar weight examples: CO2, CaCO3.
• Chemical Equilibrium and Reactions:
  • Understanding of reaction dynamics and stoichiometry.

Conclusion

• Introduction to pH and alkalinity in water systems.
• In-person lab session announcement.

Note

• Check for further updates and notices on the course platform (Canvas).