chem 1

Lesson 4: Collision Theory

Objectives

  • Describe conditions that lead to effective collisions.

  • Explain reaction rates qualitatively in terms of molecular collisions.

Collision Theory Overview

  • Definition: Chemical reactions occur during collisions between reacting particles.

  • Effective Collisions: Collisions must be effective to form products, requiring:

    • Sufficient Energy: Particles must overcome the activation energy barrier (E).

    • Proper Orientation: The orientation of particles affects the likelihood of bonding during collisions.

Factors Affecting Reaction Rates

  • Concentration: An increase in reactant concentration raises collision frequency, increasing the rate of reaction.

  • Temperature: Higher temperatures increase average kinetic energy of particles, leading to more effective collisions.

Lesson 5: Catalysis

Objectives

  • Explain the concept of activation energy.

  • Describe the catalysis process and its effect on reaction rates.

  • Differentiate between types of catalysis.

Activation Energy

  • Definition: Minimum energy needed for reactants to transform into products.

  • Catalysts: Substances that speed up reactions without undergoing permanent changes.

    • Can lower the activation energy for reactions.

Types of Catalysis

  • Homogeneous Catalysis: Catalyst is in the same state as the reactants. Forms intermediate compounds, promoting a series of lower energy steps.

  • Heterogeneous Catalysis: Catalyst is in a different state (usually solid) from the reactants, providing a surface for reactions to occur through adsorption.

Example Reactions and Processes

  • Contact Process: Produces sulfuric acid, utilizing catalysts effectively to lower the activation energy using vanadium pentoxide.

Lesson 6: Chemical Thermodynamics

Concepts

  1. Spontaneous Processes

  2. Entropy

  3. Gibbs Free Energy and Chemical Equilibrium

Spontaneous Processes

  • Definition: Processes that occur naturally without external energy. Example: Water flowing downhill is spontaneous; pumping water uphill is nonspontaneous.

  • Depend on changes in entropy and free energy.

Entropy**

  • Definition: Measure of disorder or energy dispersal within a system.

  • States:

    • Gas has the highest molar entropy, followed by liquid and solid.

Determining Entropy Changes

  • Entropy change can be quantified using the formula: [ \Delta S = \frac{q_{rev}}{T} ] where q_rev is the heat absorbed/evolved and T is the absolute temperature.

Second Law of Thermodynamics

  • Entropy of the universe increases over time.

  • A spontaneous process leads to a net increase in universe entropy, expressed as: [ \Delta S_{universe} = \Delta S_{system} + \Delta S_{surroundings} > 0 ]

Solubility of Products and Endothermic Reactions

  • Reactions can be spontaneous despite being endothermic if overall entropy increases sufficiently.

    • Example reactions illustrate how state changes impact entropy and spontaneity.

Summary of Key Formulas

  • Entropy change for reactions: [ \Delta S^{\circ} = \Sigma S^{\circ}{products} - \Sigma S^{\circ}{reactants} ]

  • Spontaneous processes result in positive entropy change for the universe.

Laboratory Activity: Effects of Factors on Reaction Rates

Objective

  • Determine how various factors—nature of reactants, concentration, temperature, and catalysts—affect reaction rates.

Experiment Components

  • Materials: Mg ribbon, Fe filings, HCl solutions, thermometer, etc.

  • Procedures include comparing reaction rates between different concentrations and types of reactants.