Advanced Chemistry Thermodynamics Notes

Advanced Chemistry Thermodynamics Notes

Advanced Chemistry Overview

• Subject: Thermodynamics
• Source: OpenStax Chemistry 2e, Chapters 5 and 16
• Author: J. Aaron Frim (updated 2022)

Objectives

Energy Basics and Calorimetry

• Source: OpenStax Chemistry 2e Chapter 5 (Sections 5:1 and 5:2)

Thermochemical Reactions

• Example Reactions:
    - Decomposition of Nitrogen Triiodide:
  $2NI_3 (s) <br /> ightarrow 3I_2(g) + N_2(g)$
    - Double Replacement and Decomposition Reaction:
      Ba(OH)_2 ullet 8H_2O(s) + 2NH_4SCN(s)
  ightarrow 7Ba(SCN)_2(s) + 2NH_3(g) + 10H_2O(l)
  
• Characteristics of Spontaneous Processes:
    - Formation of gases
    - Energy release (exothermic)
    - Energy absorption (endothermic)

Thermochemistry and Thermodynamics

• Definition of Thermochemistry:
    - Study of heat energy in relation to chemical processes.
• Definition of Thermodynamics:
    - Study of interrelations between heat, work, and other forms of energy to determine process feasibility.

Laws of Thermodynamics

1. Energy is conserved.
2. In a reversible process:
   $riangle S_{univ} = 0$
      In an irreversible (spontaneous) process:
       riangle S_{univ} > 0
3. The entropy of a pure crystalline substance is zero.

Review of Energy

• Definition of Energy:
    - The ability to supply heat or do work.
• Units of Energy:
    - Calorie (cal), Calorie (Cal), electron volt, British thermal unit (Btu), Joule (J).

Classifications of Energy

1. Potential Energy: Energy based on position or composition.
      - Examples: gravitational, chemical, mechanical, nuclear.
2. Kinetic Energy: Energy based on motion.
      - Examples: thermal, light, energy of motion, sound.

Thermal Energy, Heat, and Temperature

• Thermal Energy: Energy associated with internal movement of particles in an object.
• Temperature: Measurement of the average kinetic energy of particles.
• Heat: Energy transferred between objects at different temperatures.

Exothermic and Endothermic Processes

• Exothermic Process:
    - Heat is released to the surroundings.
• Endothermic Process:
    - Heat is absorbed from the surroundings.

Calorimetry

• Definition: A calorimeter is used to measure heat involved in a chemical or physical change.
    - All components of a calorimeter experience a change in temperature (DT) when heat is exchanged.

Components of Calorimetry

• System: Part of the universe under investigation.
• Surroundings: Part of the universe that exchanges energy with the system (the calorimeter's body and contents).

Heat Calculation

• Heat transfer equation:
  $q_{calorimeter} = q_{housing} + q_{water/solution}$
    - When heat transfer with housing is negligible:
  $q_{calorimeter} = q_{water/solution}$
    - Heat change formulas:
    - For calorimeter:
  $q_{calorimeter} = ( riangle T imes C) + (m imes riangle T imes C_p)$
    - Where:
      - C = heat capacity
      - C_p = specific heat capacity (energy needed to change 1 g of substance by 1 °C)

• Heat Transfer and Processes
    - $q_{calorimeter} = -q_{process}$
       - Negative q_process indicates exothermic, positive indicates endothermic.

Internal Energy of a System

• Definition: Summation of all energies related to an object's particles, excluding overall motion/position.
• Change in Internal Energy Equation:
  $U = q + w$
    - Represents the first law of thermodynamics. Energy is conserved.

Enthalpy

• Definition of Enthalpy (H):
    - Sum of internal energy plus work done to displace the surroundings:
  $H = U + PV$
• Change in Enthalpy Equation:
  $riangle H = riangle U + P riangle V$
  $riangle H = (q + w) + P riangle V$

State Functions in Enthalpy

• State Function: Value determined by initial and final states of a system, independent of pathway.
• Enthalpy as a State Function:
  $riangle H = H_{final} - H_{initial}$

Thermochemical Equations

• Definition: Shows matter and energy changes during a reaction, with associated enthalpy changes.
• Examples of Thermochemical Changes:
    -
      - For example, a reaction incorporates the enthalpy change directly into the equation:
  $2H_{2}(g) + O_{2}(g) <br /> ightarrow 2H_{2}O(g) riangle H = -241$
  

1. Doubling moles doubles enthalpy change.
2. Reversing a reaction flips sign of enthalpy change.

Hess’s Law

• Definition: Total enthalpy change is equal to the sum of changes of individual steps in a process.
• Example Calculation for Methane Formation:
• Given reactions:
    1. $C + H_{2} <br /> ightarrow CH_{4} riangle H = ?$
    2. Simple previous reactions edited with somenumbers to encompass data needed.

Enthalpy of Formation

• Definition: Process of forming a substance from constituents in their standard state at 25 °C and 1 atm.
• Example Reaction:
  $6C(s) + 6H_{2}(g) + 3O_{2}(g) <br /> ightarrow C_{6}H_{12}O_{6}(s) riangle H = -1271 ext{ kJ/mol}$

Application of Hess’s Law

• Equation:
  $riangle H^{ ext{o}} = ext{Sum of products } riangle H^{ ext{o}} - ext{Sum of reactants } riangle H^{ ext{o}}$
• Conditions: Standard conditions, 1 atm; purification and co-efficient reactions consideration needed.

Spontaneity and Entropy

• Source: OpenStax Chemistry 2e Chapter 16 (Sections 16:1 - 16:3)

Spontaneous Processes

• Definition: A spontaneous process occurs without the continuous addition of energy.
• Characteristics:
    - Increase the universe's entropy.
    - Can be exothermic or endothermic.
    - Activation energy needed for many spontaneous processes.

Examples of Activation Energy in Spontaneous Processes

• Diffusion, melting of ice, combustion of glucose.
• Non-spontaneous processes require additional energy (work) to occur, such as the purification of seawater and freezing water at room temperature.

Three Laws of Thermodynamics

1. Energy is conserved.
2. $riangle S_{univ} ext{ for reversible} = 0$; riangle S_{univ} > 0 ext{ for irreversible}.
3. Entropy of a pure crystalline substance is zero at absolute zero.

Understanding Entropy

• Definition of Entropy (S): A measure of energy and matter distribution. Often viewed as a measure of disorder.
• Entropy Equation for Irreversible Processes:
     riangle S = rac{q_{reversible}}{T}
• Boltzmann Equation for Entropy:
  $S = k ext{ln} W$ where
    - k = Boltzmann constant,
    - W = number of microstates.

Second Law of Thermodynamics

• Statement: Any spontaneous process must be accompanied by increasing entropy of the universe:
  $riangle S_{univ} = riangle S_{system} + riangle S_{surroundings}$
    - riangle S_{univ} > 0 for spontaneous processes.
• Note: Spontaneous change can involve a decrease in system entropy.

Temperature Dependence of Spontaneity

• Example: Water Freezing Analysis:
• Conditions assessed at different temperatures to predict spontaneity of freezing:
• Equations at Varying T:
    - riangle S_{univ} = riangle S_{system} + ( -rac{q_{reversible}}{T_{surroundings}})

Temperature Effects on Entropy

• High temperature leads to lower probability of spontaneity; process assessment varies by increasing or decreasing temperatures.

Predicting Spontaneity with Gibbs Free Energy (G)

• Free Energy Equation:
  $G = H - TS$
    - Spontaneity Criteria:
     - If $riangle G < 0$, process is spontaneous.    - If $riangle G > 0$, process is not spontaneous.
     - If $riangle G = 0$, system is at equilibrium.

Gibbs Free Energy Calculation

• Free energy change based on initial and final states; depends on:
  $riangle G^{ ext{o}} = ext{Sum}(n imes riangle G^{ ext{o}}<em>{products}) - ext{Sum}(n imes riangle G^{ ext{o}}</em>{reactants})$

Non-standard Conditions and the Reaction Quotient (Q)

• Q Definition: Ratio showing a reaction's progress.
• Equations for Non-standard Conditions:
  $riangle G = riangle G^{ ext{o}} + RT ext{ln}Q$
    - Where R = universal gas constant, T = temperature in Kelvin.

Reaction and Free Energy Dependency

• Equilibrium and Free Energy:
    - At equilibrium, $riangle G = 0$ and the reaction quotient equals the equilibrium constant (K).
    - Analyzing progress of reactions based on Gibbs Free Energy calculations determines spontaneity direction (positive/negative reactions).

Final Thoughts

• Free Energy as a significant measure to assess reaction spontaneity, available work, and system state.
• The concepts in thermodynamics combine heat, work, and energy transfer mechanisms to characterize spontaneous processes and their related energetics.