CH 8 CH 5

Week 8 Overview

  • Topics: 5.8, 8.2-8.5, Redox Reactions (5.3)

Objectives

  • Recognize chemical reaction types.
  • Balance chemical equations.
  • Predict reaction rate effects due to temperature/concentration changes.
  • Define oxidation/reduction; apply concepts in contexts like batteries and cell respiration.

Reaction Rates (8.2)

  • Reaction rate: speed at which concentration of reactants/products changes.
  • Formula:
    Rate=ΔCΔt=C<em>f−C</em>0Δt\text{Rate} = \frac{\Delta C}{\Delta t} = \frac{C<em>f - C</em>0}{\Delta t}
  • Fast: reactants convert to products quickly; slow: vice versa.

Reaction Mechanism Assumptions (8.3)

  1. Reactant particles collide.
  2. Correct orientation for reaction.
  3. Minimum energy (activation energy) needed to react.

Energy Diagrams (8.4)

  • Show energy (y-axis) vs. time (x-axis).
  • Key features:
    • Energy of reactants/products shown statically.
    • Energy changes depicted by curves during the reaction.

Energy Changes in Reactions

  • Step 1: Energy needed to break bonds (activation energy).
  • Step 2: Energy released from forming bonds (enthalpy).
  • Outcomes:
    • Endothermic: net positive energy change (absorbs heat).
    • Exothermic: net negative energy change (releases heat).

Factors Increasing Reaction Rate (8.5)

  1. Concentration: Higher concentration leads to more collisions.
  2. Temperature: Higher temperature increases particle speed and collision energy.
  3. Catalysts: Speed up reactions by lowering activation energy.

Redox Reactions (5.3)

  • Electrons transfer reactions.
  • Oxidation: loss of electrons; Reduction: gain of electrons.
  • Both processes are interconnected.

Identifying Redox Reactions

  • Oxidation occurs when a substance reacts with O2.
  • Metals generally oxidized when reacting with nonmetals.

Oxidation Numbers

  • Use to identify oxidation/reduction in reactions.
  • Increase (more positive) indicates oxidation; decrease (more negative) indicates reduction.

Assigning Oxidation Numbers

  1. Element by itself: 0.
  2. Ion charge equals oxidation number.
  3. Group 1: +1, Group 2: +2.
  4. Hydrogen in compounds: +1.
  5. Oxygen in compounds: -2.

Examples and Applications

  • Example Reaction: Copper wire in silver nitrate activates oxidation/reduction. - Common examples: batteries, cellular respiration, combustion, photosynthesis, rusting.

Homework

  • Chapter 8 Exercises: 8.10, 8.22, 8.26, etc.
  • Chapter 5 Exercises: 5.2, 5.4, etc.