Explore Chemistry for Biology Students with these specialized notes crafted for Year 1 students at University College London. Within this document, unravel the intricacies of ions and chemical forces, exploring concepts such as equilibrium, reaction quotients, Gibbs energy, protons, pH, solubility,...
D1: Introduction to Equilibrium, Reaction Quotients and Gibbs Energy
Ions and Forces
Aims and objectives
o Relate equilibrium constants, quotient with Gibbs free energy of reactions
o Distinguish between acid and conjugate acid and base and conjugate base
o Design a buffer and calculate the buffer pH using the Henderson-Hasselbalch equation
o Split redox reactions into oxidation and reduction reactions
o Calculate standard electrochemical potentials for electrochemical cells
o Calculate the chemical change at an electrode surface from the current passed through an
electrolyte
What makes cell processes tick?
o Biological systems
Highly organised
Systems described in individual chemical reactions
In reality – the chemical reactions are closely linked
o Cells
Organelles
Have particular roles
Can be extracted and studied chemically
Equilibrium
Fundamental concepts in chemistry
o Kinetics
How quickly or slowly a reaction occurs
o Thermodynamics
Changes in the form of energy when a reaction occurs – e.g. converting chemical energy to
heat
o Equilibrium
Reactions in which the reactants and products coexist
o Reversibility of chemical change
Reactions occurs until no change in chemical composition
E.g. ATP ADP + Pi
o A – Start with ADP and phosphate + no ATP
Concentrations of ADP and Pi will deplete
Concentrations of ATP increases
Until equilibrium concentrations are
achieved
o B – Start with ATP only + no ADP and phosphate
Concentrations of ATP will deplete
Concentrations of ADP and Pi increases
Until equilibrium concentrations are
achieved
o No matter where you start from – the reaction
occurs
Equilibrium
o aA + bB cC + dD
Reactants = A, B
Products = C, D
o Equilibrium constant K
Kc = ([C]c[D]d) /([A]a[B]b) = [products] / [reactants]
,D1: Introduction to Equilibrium, Reaction Quotients and Gibbs Energy
Kp = ((PC)c(PD)d)/ ((PA)a(PB)b) = (Pproducts) / (Preactants)
K = constant for a given reaction at a particular temperature and pressure
Units
o Kc – solutions
Concentration – moldm-3 or moldkg-1
o Kp – gases
Pressure – Pa or bar
Large K
o Equilibrium favours product formation
Small K
o Equilibrium favours reactant formation
o ∆rG
∆G = ∆H - T∆S
Energy associated with a chemical reaction that can be used to do work
o Negative ∆rG
Equilibrium favours product formation
o Positive ∆rG
Equilibrium favours reactant formation
G – total Gibbs energy of the system
Chemical potential = G / n = Gibbs energy / number of moles
o Reaction quotient Q
Measures relative amounts of products and reactants present during a reaction at a
particular point in time
Qc = ([C]c[D]d)/ ([A]a[B]b)
o
Describes the progress of the reaction
Solids and pure liquids are in their standard state and always equal to 1
, D1: Introduction to Equilibrium, Reaction Quotients and Gibbs Energy
o
More on Equilibrium and Gibbs Energy
o Equilibrium
Dynamic process in which the forward and backward reactions occur in balance
∆rG = ∆rG0 + RTlnQ
o Q = reaction quotient
o ∆rG0 = Gibbs energy at standard conditions
o R = gas constant
o T = temperature
o K is at the bottom of the curve
Right of K = positive gradient
Left of K = negative gradient
Q<K
o Reaction will favour products
o ∆rG = negative
o A+BC+D
Q>K
o Reaction will favour reactants
o ∆rG = positive
o A+BC+D
Q=K
o System is at equilibrium
o ∆rG = 0
o A+BC+D
o ∆rG = - RTlnK
pH
o Protons – H3O+
Do not exist as H+ - exist as H3O+
Controls:
Enzyme activity
Synthesis of ATP
Oxygen transport
Charge on proteins and lipids
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