Physical Biochemistry - Solution Chemistry for the Biosciences

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Concentration - means by which amount of material in a given quantity of solution is expressed.

If molecules are distributed on a molecular basis, system is referred to as a solution, and the dissolved material is the solute.

We usually use the term solution to refer to solutes in a liquid solvent.

If the materials are dispersed as particles, the system is referred to as a suspension or dispersion.

Molecule is big, 10Angstroms, lots of atoms make it.

Particle 10-100μm

In between = colloids 10-1000nm

Molarity - number of moles of solute in 1L of solution

Molality - number of moles of solute in 1000g of solvent

Mole fraction - is the number of moles of solute divided by the total number of moles of solute and solvent.

% w/v - g of solute in 100ml solution

% w/w - g of solute in 100g of solution

Principles of Chemical Equilibrium

  • Some reactions proceed to completion
  • Many reach equilibrium whereby the rates of the forward and reverse reactions are equal (dynamic equilibrium)
  • this is given by the equilibrium constant K.
  • K= (Products)/(Reactants)

Law of Mass Action: Every Reaction has its own equilibrium constant expression

  • aA + bB = cC + dD
  • K= (C)^c(D)^d/(A)^a(B)^b
  • constant at given temperature
  • the equilibrium constant expression depends only on the stoichiometry of the reaction, not on its mechanism.
  • if K is known, we can predict the concentrations at equilibrium
  • K tells us the extent of the reaction

Free energy (G) - system will go from high to low free energy spontaneously until energy state of reactants and products the same (ΔG=0)

Chemical potential μ

How much does the free energy increase by adding 1 mole of a substance to a solution?

  • High chemical potential - addition causes free energy to increase a great deal - results in high free energy for system
  • Low chemical potential - addition causes free energy to increase only slightly
  • Higher free energy of system = higher driver for spontaneous reaction
  • Everything tries to lose its free energy to the surroundings.

2 materials (reactant

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