SectionC8_BB - Tagged
CHEM10021 Chemistry for Bioscientists I: Equilibrium Notes
Page 1: Introduction to Equilibrium
University Context: Course on Chemistry for Bioscientists I, Section C8 focusing on the topic of Equilibrium.
Reference Year: Content relates to the context of Manchester in 1824.
Page 2: Chemical Equilibrium
Forward and Reverse Reactions: Every forward reaction has an accompanying reverse reaction.
Equilibrium Representation:
Conc. [P] R P
At equilibrium, the rate of formation of products equals the rate of decomposition of reactants.
Dynamic Chemical Equilibrium: A state where the concentrations of reactants and products remain constant over time as they are continuously formed and decomposed.
Page 3: Gibbs Energy and Equilibrium
Gibbs Energy Relation: When ∆G = 0, a reaction is at equilibrium.
Minimum Gibbs Energy: At equilibrium, the Gibbs energy is minimized; excess reactants or products will not lower Gibbs energy.
Extent of Reaction: Concentration changes do not drive the system away from its Gibbs energy state at equilibrium.
Page 4: Reaction Quotient, Q
Arbitrary Concentrations: To calculate
∆G for arbitrary concentrations, we reference the standard Gibbs energy change (∆G°) which assumes standard concentrations for reactants/products.
Composition Calculation: The equilibrium composition can be calculated using the reaction quotient, Q.
Page 5: Gibbs Energy of a Reaction
Gibbs Energy Change: Defined for a theoretical reaction with 1 mole of reactants/products at standard conditions.
Formula:
∆G° = ∆H° - T∆S°
Variables:
∆H°: Standard enthalpy change
T: Absolute temperature
∆S°: Standard entropy change
Page 6: Biological Standard State
Chemical Standard State: Typically defined at 1 mol dm⁻³ concentrations.
Biological Standard State: Maintains 1 mol dm⁻³ & pH 7 (with [H⁺]=10⁻⁷ mol dm⁻³).
Gibbs Energy Terminology:
∆G°: Used for the chemical standard state.
∆G⁺: Used for the biological standard state.
Page 7: Reaction Quotient Q Definition
General Reaction Representation:
aA + bB ⇌ cC + dD
Q Formula:
Q = [C]ⁱ[D]ʳ/[A]ᵃ[B]ᵇ
Meaning of Q: The reaction quotient provides a measure of the relative amounts of products and reactants at any point.
Page 8: Thermodynamic Activity and Q
Activity: A dimensionless quantity that generalizes Q to different phases: solutions, solids, gases.
Concentration Influence:
For ideal solutions: Activity equals molarity.
Concentration example: If "A" = 0.1 mol dm⁻³, then activity = 0.1.
Pure Substances: For pure solids/liquids, activity is unity (1) and can be omitted.
Gases: Their activity equals their partial pressure in bar.
Page 9: Measuring Reaction Quotient Q
Q Calculation:
Q = [C]ⁱ[D]ʳ/[A]ᵃ[B]ᵇ
Purpose of Q: Measures the current concentrations of reactants and products, reflecting the system's state.
Page 10: Gibbs Energy Change for Arbitrary Concentrations
Relation of Gibbs Energy:
The Gibbs energy change for arbitrary concentrations (∆G) connects with standard Gibbs change (∆G°) via:
∆G = ∆G° + RT ln(Q)
R is the universal gas constant.
Page 11: Continuation of Chemistry for Bioscientists I
Section Reference: Continuation from previous content outlining the key principles of chemical equilibrium.