Gen Chem 1202

Previously covered topics:
- The rate of any chemical reaction is controlled by activation energy.
- Chemical equilibrium occurs when a given reaction and its reverse reaction transpire simultaneously.
- Enthalpy change in a system refers to the heat exchanged between the system and its environment during a constant-pressure process.
Focus: Explore connection between energy and extent of reaction.

Key concepts to understand:
- Relationship of entropy, enthalpy, and temperature in determining if a reaction occurs.
- Spontaneous vs Non-spontaneous processes.
Calculation skills required:
- Determine entropy change.
- Calculate Gibb’s free energy.

Chemical Thermodynamics: Area of chemistry dealing with energy relationships. Key concepts include:
- First Law of Thermodynamics:
1. Energy is conserved.
2. Energy can transfer between a system and surroundings.
3. Energy can change forms.
4. Total energy of the universe remains constant.
- Equation: $riangle E = q + w$
- Where:
  - $riangle E$ = Change in internal energy of the system
  - $q$ = Heat absorbed or released by the system from (or to) surroundings
  - $w$ = Work done on/by the system

Helps track heat and work transferred between a system and surroundings; however, it does not indicate process favorability.
Heat movement:
- If the heat of the system decreases, the surroundings gain energy and vice versa. Direction of heat flow is unspecified.
Certain processes occur naturally despite the conservation of energy.

Spontaneous Process: One that proceeds without outside assistance (e.g., burning wood, heat transfer from hot stove to pot, books falling).
Non-spontaneous Process: Requires energy input from an external source (e.g., CO2 forming gasoline, ozone formation driven by UV light, photosynthesis).
Directionality: Spontaneous processes occur in one direction. The reverse is always non-spontaneous.

Spontaneous Examples:
- Gas expanding into a vacuum.
- Perfume diffusing in a room (gases spread out).
Non-spontaneous Examples:
- Gas moving back to one flask from expansion.

A spontaneous reaction occurs on its own accord regardless of speed:
- Fast reaction example: Acid-base neutralization.
- Slow reaction example: Iron rusting.
Chemical thermodynamics indicates direction and extent but not the speed of reactions.

Definition: Entropy reflects the statistical probability of different energy states of matter.
Significance: Associated with randomness in a system and energy distribution among molecular motions. Focus on overall state changes or microstates.
Connection to spontaneity and the Second Law of Thermodynamics: Used to predict whether a process is spontaneous based on entropy.

Microstate Consideration:
- Involves the relative positions and speeds of molecules.
- A single mole contains approximately $6.02 imes 10^{23}$ molecules, leading to many microstate possibilities.
Types of Motion in Chemistry:
- Vibrational, Rotational, and Translational Motion.

Gas has more microstates than solids, leading to higher entropy.
Dissolution: Examples such as dissolving NH4NO3 salt, which requires energy, illustrate endothermic processes leading to increased entropy despite a positive $riangle H$ .

A system's final state is more favorable if:
1. Energy disperses among a larger variety of molecules.
2. Particles are more dispersed (disordered).
State Function: Entropy is a property described by the state function, with change computed as:
$riangle S = S<em>{final} - S</em>{initial}$
Values depend solely on initial and final states, independent of the path taken.

States that the entropy of a pure crystalline substance at absolute zero (0.0 K) is zero: $S = 0.0 ext{ J/K·mol}$ .
Sign Notation:
- Positive $riangle S$ : Increasing disorder.
- Negative $riangle S$ : Decreasing disorder, though it may still proceed.

Defined at standard conditions (pure substance at 1 atm pressure, measured at 298 K).
Increase in S° with:
- Atomic mass.
- Number of atoms.
- Transition from solid to liquid or gas.
Qualitative guidelines for entropy changes based on physical states and reaction complexity will be discussed in detail, such as:
1. Solvent dissolution of solids or liquids increases S°.
2. Increased number of molecules increases S° (consider the conversion of $N2O4(g)$ to $2 NO2(g)$ ).

Rules for calculating reaction entropy changes ( riangle S) include:
Calculate based on coefficients from the balanced chemical equation:
$riangle S<em>{rxn} = ext{Sum of } riangle S</em>{products} - ext{Sum of } riangle S_{reactants}$
Guiding factors include phase changes and changes in the number of gaseous molecules.

Spontaneity relates to both entropy and enthalpy. Gibbs free energy (G) combines these elements at constant temperature and pressure. Define:
- $riangle G = riangle H - T riangle S$
Interpretations of ΔG:
- riangle G < 0: Spontaneous reaction.
- $riangle G = 0$ : Equilibrium.
- riangle G > 0: Non-spontaneous reaction.

Reminder: Entropies measured in $ext{J/mol·K}$ , while enthalpies and free energies are in $ext{kJ/mol}$ .
Ensure consistency in unit conversions when performing calculations involving ΔS and ΔH together.

Understand spontaneity in the context of enthalpy and energy dispersal.
Explore entropy further through problems calculating both ΔG and Ksp under various conditions.

Students should tackle several problems to understand concepts of ΔG, especially focusing on how factors such as temperature influence spontaneity as explored through practical examples.

Focus on understanding the nuances of entropy, free energy, and their relevance in a variety of chemical reactions and transformations, linking theoretical concepts to real-world applications, ultimately leading to mastery in predicting spontaneity and system behaviors across different conditions.