Lecture 14 Chemical Equilibrium Highlighted

Equilibrium Description
- Understand equilibrium in terms of forward and reverse reaction rates.
- Define equilibrium in terms of its position within a chemical reaction.
- Explain changes in forward and reverse reaction rates to achieve equilibrium.
Equilibrium Expressions
- Learn to write equilibrium constant expressions for chemical reactions.
- Calculate equilibrium constant values for given reactions.
- Interpret the significance of the equilibrium constant's magnitude.
Rate Constants and Predictions
- Describe equilibrium constants in relation to rate constants for reactions.
- Predict how equilibrium shifts with disturbances in reactants/products.
- Assess the effect of temperature changes on equilibrium.

Definition
- Dynamic equilibrium is achieved when the forward reaction rate equals the reverse reaction rate.
Reversible Reactions
- A reversible reaction allows the reverse reaction to significantly impact the overall reaction.

Extent of Reaction
- Dynamic equilibrium can occur at any stage of a reaction, indicating varying concentrations of reactants and products.
Describing Equilibrium Position
- Equilibrium conditions can be assessed (e.g., equilibrium lies left, middle, or right) based on the concentrations of products and reactants.

Effect of Concentration
- Reaction rates are influenced by the concentration of reactants: higher concentrations result in faster reaction rates.
- For the forward reaction: Rate = k_forward[Reactants]^order
- For the reverse reaction: Rate = k_reverse[Products]^order
Reverse Reaction Rate
- Increased product concentration speeds up the reverse reaction.

Definition
- Keq reflects the position of equilibrium at a specified temperature for a given reaction.
Multi-step Reactions
- Formulation of the equilibrium constant for multi-step reactions follows a generalized expression:
  - For a reaction: aA + bB ⇌ cC + dD, the equilibrium constant is written as:[ K_{eq} = \frac{[C]^c[D]^d}{[A]^a[B]^b} ]
Example: For the reaction 2 SO(g) + O(g) ⇌ 2 SO3(g),
- [ K_{eq} = \frac{[SO3]^2}{[SO]^2[O]} ]

Magnitude of Keq
If Keq > 1000, the reaction strongly favors products.
If Keq < 1000, the reaction favors reactants.
- Specific Cases:
  - Keq < 10^-3: Reaction barely occurs; equilibrium lies far left.
  - Keq between 10^-3 and 10^3: Mixture of reactants and products present at equilibrium.
  - Keq > 10^3: Mostly products present at equilibrium, favoring reaction completion.

Principle Overview
- If an equilibrium is disturbed, it shifts to counteract the disturbance and restore equilibrium.
Reaction Example
- Adding SO3 to the reaction 2 SO2 + O2 ⇌ 2 SO3 shifts the equilibrium left, increasing SO2 and O2 while decreasing SO3.

Temperature Influence
- Temperature changes can influence the shift of equilibrium in reactions:
- For exothermic reactions, removing heat by cooling shifts equilibrium right, while adding heat shifts it left.
Reaction Context
- In an endothermic reaction, lowering temperature (removing heat) shifts equilibrium left.

Writing Equilibrium Expressions
- For the reaction: PbCl2(s) ⇌ Pb2+(aq) + 2 Cl–(aq):
- Ksp = [Pb2+][Cl–]^2
Understanding Solubility
- Solubility equilibria define how much insoluble material can dissolve. E.g., FeS(s) ⇌ Fe2+(aq) + S2–(aq).
Solubility Product (Ksp)
- Ksp is defined for sparingly soluble salts with similar formulation:[ K_{sp} = [Fe2+][S2–] ]

Sample Ksp Values
- Providing a comparison of solubility for various salts aids in determining the most soluble compounds at a specified temperature:
  - E.g., magnesium carbonate has the highest Ksp value at 4.0 × 10^-5, indicating it is the most soluble salt listed.
Utilization of Ksp
- A low Ksp signifies sparingly soluble compounds and indicatively organizes compounds based on their solubility in saturated solutions.