Chemical Equilibrium and Acid-Base Reaction Principles

Dynamic Equilibrium and System Properties

1. Dynamic Equilibrium (⇄): This is a dynamic, not static, state. Temperature relates to the speed of molecules. Concentration formulas include C = n/v, n = C * v, and v = n/C.

• Rate: The rate of the forward reaction equals the rate of the reverse reaction.
• Concentration: Concentrations remain constant at equilibrium, though they are not necessarily equal.
• Molecules: Molecules are destroyed and created at the same speed.
• System Type: Must be a closed system where no matter flows in or out. It requires constant temperature (no phase change, color change, or pressure change).

Inert Gases and Catalysts

• Inert Gases: Adding an inert gas (e.g., Ar, He) results in no shift in equilibrium.
• Catalysts: Adding a catalyst allows the system to reach equilibrium faster, but causes no shift and the K_c remains constant.

Percent Yield and Reaction Favorability

2. Percent Yield: Measures how close a reaction got to finishing. Look for terms like 'lab experiment', 'produced', or 'collected'.

• Formula: % Yield = (Experimental Yield / Theoretical Yield) x 100.
• Interpretation:
  • < 50%: Prefers staying as reactants.
  • > 50%: Prefers staying as products.
  • > 99%: Quantitative reaction.

The Equilibrium Constant (Kc)

3. Kc Formula and Calculations: The ratio of products to reactants inside the final equilibrium mixture. K_c indicates if the reaction favors products or reactants at equilibrium.

• Formula: K_c = [C]^c [D]^d / [A]^a [B]^b.
• Usage: Use if equilibrium concentrations are given. Look for equilibrium concentration, ICE tables, or initial amounts.
• Values:
  • K_c > 1: Products are favored at equilibrium.
  • K_c < 1: Reactants are favored at equilibrium.
• Rules: Only temperature can change the value of K_c. Include gases (g) and aqueous (aq) solutions. Omit pure solids (s) and liquids (l) as their concentrations do not change.

Le Châtelier’s Principle and Predicting Shifts

4. Predicting Shifts: When a system is stressed, it shifts to dilute that stress.

• Concentration ([ ]) Changes:
  • ↑ [Reactant] or ↓ [Product] → Shift RIGHT (→).
  • ↓ [Reactant] or ↑ [Product] → Shift LEFT (←).
• Volume (V) and Pressure (P) Changes (Gases Only):
  • ↓ Volume (↑ Pressure) → Shift to the side with fewer gas molecules.
  • ↑ Volume (↓ Pressure) → Shift to the side with more gas molecules.
• Temperature (T) Changes:
  • Endothermic: ↑ Temp → Shift Right, K_c ↑, more products.
  • Exothermic: ↑ Temp → Shift Left, K_c ↓, more reactants.

Graph Analysis and ICE Tables

5. Graph Reading:

• If all lines spike up or down: Indicates a volume or pressure change.
• If there is no spike but a smooth curve: Indicates a temperature change.
• If only one line spikes up or down: Indicates a chemical was added or removed.

6. ICE Tables (Initial, Change, Equilibrium): Used when initial values and at least one equilibrium value are given.

• Reactants (Left): Initial - Change = Equilibrium.
• Products (Right): Initial + Change = Equilibrium.
• Note: Only the 'Change' row can use coefficients from the balanced equation.

Brønsted-Lowry Theory and Net Ionic Equations

7. Brønsted-Lowry Acids and Bases:

• Acid: Loses H⁺ to become a Conjugate Base (charge ↓).
• Base: Gains H⁺ to become a Conjugate Acid (charge ↑).

8. Net Ionic Equations: When adding water, split metals into ions. Keep weak acids and molecules whole. For strong acids (SA), scan the left of the table; for strong bases (SB), scan the right. Quantitative reactions use a single arrow (→), while equilibrium reactions use a double arrow (⇆).

pH and pOH Calculations

9. Logarithmic Scales: For significant figures, ignore the numbers before the decimal point.

• Formulas:
  • pH = -log[H₃O⁺]
  • pOH = -log[OH^-]
  • [H₃O⁺] = 10^-pH
  • [OH^-] = 10^-pOH
  • pH + pOH = 14.00
  • K_w = [H₃O⁺][OH^-] = 1.0 x 10^-14
• pH Levels:
  • Concentration > 1.0 M: Negative pH (Ultra Acid).
  • Concentration < 1.0 M: Positive pH (0–6.9 is Acidic).
  • pH 7.0: Neutral (Pure water, [H₃O⁺] = [OH^-]).
  • pH 7.1–14: Basic (Requires the '14-minus' trick).

Chemical Nomenclature

10. Naming Chemicals:

• If it says 'Acid': Copy the name from the Acid Chart.
• If it ends in '-ite' or '-ate': Copy from the Polyatomic Ion Chart.

Predicting Acid-Base Reactions

12. Reaction Favorability: To predict which side is favored when mixing two substances:

1. List all entities.
2. Identify the Strongest Acid (SA) and Strongest Base (SB) using the data book.
3. Write the proton transfer equation.
4. Spontaneity Rules:
   • SA above SB: Spontaneous (> 50%), K_c > 1, products favored.
   • SA below SB: Non-spontaneous (< 50%), K_c < 1, reactants favored.
   • Top 6 Strong Acids: Quantitative (> 99%), use a single arrow.

Percent Ionization and Weak Systems

13. Percent Ionization: Measures how much a weak acid or base dissociates. This involves finding [H₃O⁺] or [OH^-] when no equilibrium concentrations are given.

• The 1000 Test: Test if the shortcut can be used: Initial Concentration / K_a (or K_b). If the answer is > 1000, use the shortcut. If < 1000, use the full ICE method.
• Weak Acid Shortcut: [H₃O⁺] = √(K_a * C_acid).
• Weak Base Shortcut: First find K_b (K_b = 1.0 x 10^-14 / K_a), then [OH^-] = √(K_b * C_base).