Chemistry for Engineering Technologists

Learning Outcomes

  • Balance chemical equations: Understand electron transfer in reactions.
  • Definitions:
    • Anode: Electrode where oxidation occurs.
    • Cathode: Electrode where reduction occurs.
    • Oxidation: Loss of electrons.
    • Reduction: Gain of electrons.
  • Compute cell potential: Calculate electrochemical energy of galvanic cells under standard and non-standard conditions.
  • Distinguish cell types: Differentiate between galvanic and electrolytic cells.
  • Compute current, time, or charge: Calculate these in electrolytic processes.

Electrochemical Basics

  • Oxidation-Reduction Reactions:
    • Spontaneous reactions convert energy to electricity.
    • Non-spontaneous reactions require electrical energy.

Oxidation Numbers

  • Charge assigned to an atom in a molecule or ions can be calculated as:
    • Free elements: 0
    • Monatomic ions: equal to ion charge
    • Oxygen: usually -2 (varies in peroxides)
    • Hydrogen: +1 unless bonded to metals (then -1)
  • The sum of oxidation numbers equals the charge of the compound.

Balancing Redox Equations

  1. Write unbalanced ionic form reactions.
  2. Create half-reactions for oxidation and reduction.
  3. Balance atoms (O, H) with H2O and H+ in acidic environments.
  4. Balance charges with electrons.
  5. Equalize electrons and combine half-reactions.

Galvanic Cells

  • Components: Anode and cathode along with salt bridge and solutions.
  • Cell voltage (emf) = difference in potential between anode and cathode.
    • Cell Diagram:
      extZn(s)∣Zn2+(1extM)∣∣extCu2+(1extM)∣extCu(s)ext{Zn (s) | Zn}^{2+} (1 ext{M}) || ext{Cu}^{2+} (1 ext{M}) | ext{Cu (s)}

Standard Reduction Potentials

  • Standard Conditions: 1 M concentration and gases at 1 atm.
  • More positive potentials indicate greater tendency for reduction.

Nernst Equation

  • Formula: E=E0−RTnFln(Q)E = E^0 - \frac{RT}{nF} ln(Q)
  • Relates concentration and cell potential under non-standard conditions.

Electrolysis

  • Process: Uses electrical energy to drive nonspontaneous reactions.
  • Key Components: Current (A), time (s), and Faraday's laws of electrolysis.
  • Products of electrolysis can be calculated by relating current and charge using:
    extCharge(C)=extCurrent(A)imesextTime(s)ext{Charge (C)} = ext{Current (A)} imes ext{Time (s)}

Self-Checks

  • Practice balancing redox equations and calculating standard emf and concentration effects in cells.
  • Solve problems regarding electrolysis, such as determining quantities of products formed under specified conditions.