PhysChemBasics#4: Affinity 101 The 1st and 2nd law are statements about energy and entropy in the universe. We can measure the change in energy and entropy during a process and are also able to calculate these quantities using thermodynamic tables. We may combine energy and entropy using the Gibbs Helmholtz equation and arrive at Gibbs Free Energy which is a measure of instability. It tells us whether or not a process will run spontaneously.

PhysChemBasics#1: Change of State 101 Thermodynamics investigates systems – specified regions of the universe. Thermodynamics describes the state of a system using state functions like temperature and volume and also invents new state functions (enthalpy, entropy and free energy) to apply the universal laws of thermodynamics. Thermodynamics call the change of state a "process" and describe it quantitatively using "delta quantities" of state functions and work and heat, which are path functions. As the name implies, path functions are path-dependent, thus the exact path of the process has to be specified. In this lecture, some useful equations are discussed: Gibbs' phase rule to calculate the degrees of freedom of a system, the equation for calculating the sensible heat and the equations for calculating electrical and pressure volume work.

PhysChemBasics#5: Chemical Equilibrium The affinity of a process has two contributions - an energetic contribution delta (H) and an entropic contribution delta (S). Temperature always increases the contribution of entropy. Sign and magnitude of delta (H) and delta (S) and temperature determine the chemical driving force delta G°. Standard Gibbs Free energy (G) ° corresponds to the difference in instability of reactants and products. From delta (G) ° we can calculate the equilibrium constant K (eq). The temperature dependence of the equilibrium constant is described by van't Hoff's equation. Qualitatively , we can discuss the shifting of equilibria with Le Chateliers principle (the principle of least constraint/stress).

(PhysChemBasics#11) For an adequate description of an electrolyte we have to consider its ionic strength and its activity. In addition to the classical electrical conductivity kappa, molar conductivity lambda was introduced for electrolytes. Both anions and cations contribute to this propery, their proportion can be quantified using the transport numbers.

(PhysChemBasics#12) The combination of an electronic conductor with an eletrolytic conductor is referred to as an electrode. An electrode may be quantitatively described by the electrode reaction and by the electrode potential. The electrode potential depends on the concentration, which can be described according to Nernst. The amount of material converted at an electrode is described by Faraday's law. We may combine 2 electrodes to build up a galvanic cell. The open circuit voltage or EMF of these cells corresponds to the difference between the electrode potentials.

PhysChemBasics#2 Gases 101 The state of an ideal gas can be calculated using the ideal gas law. The composition of gas mixtures can be given using Dalton's partial pressures. Microscopically a gas can be described by Maxwell-Boltzmann theory with the parameters average speed and mean free path being most important. Deviatons from the ideal behavior can be quantified using the van-der-Waals equation, which explains why at the critical point a gas behaves only "3/8 idealy".

PhysChemBasics#8 Phase Diagrams 101 The best way to discuss phase diagrams is to first look for the homogeneous and heterogeneous regeions, then label the binodals and draw in some tie lines. Finaly depict the invariant points and specify the processes that take place at these points. Ideal phase diagrams, whether melting or boiling phase diagrams, show neither maximum nor minimum for the binodals. Non-ideal mixtures may have maxima and minima, which are called azeotrope, peritectic or eutectic, depending on the type of diagram. Gibbs' phase triangle has proven useful for the illustration of 3-component mixtures. Again there may be binodals and tie lines in this diagram. A tie line not only tells us the composition of the phases in the heterogeneous region, but also - after applying the lever rule - their quantity ratio..

(PhysChemBasics#9) The concentration of a reactant can act on the reaction rate in different ways. This is quantified by the reaction order. Depending on the reaction order, there are different rate laws, concentration-time functions and half-lives. A reaction can be microscopically illustrated by the reaction coordinate diagram (energy profile). Its maximum - the transition state - is relevant for the reaction rate. With the Arrhenius equation we can quantify the influence of temperature on the reaction rate. We obtain the kinetic parameters of activation energy and frequency factor by evaluating the data using the Arrhenius plot. If we know the parameters, we can determine rate constants, conversion rates and reaction times for any temperature. Influences on reaction rate by catalysts, solvents and ionic strength may be quantified by Eyring's transition state theory.

(PhysChemBasics#10) In reversible reactions, the rates of the reverse and forward reaction are equal at equilibrium, the law of mass action can thus be derived kinetically. The energy profile tells us, that there is a simple relationship between activation energies and the enthalpy of reaction. With consecutive reactions and reactive intermediates, the steady state approximation applies: the concentration of the intermediate is approximately 0 and does not change with time. With parallel reactions, the reaction with the lower activation energy dominates - provided the reaction is kinetically controlled.

The thermodynamics of mixing can be described according to the theory of Flory and Huggins; with so called ideal solutions, there is no heat of mixing and the Flory-Huggins parameter chi = 0. A solution always shows a lower vapor pressure than the pure solvent which can be calculated with Raoult's 1st law. A solution has both a higher boiling point and a lower freezing point than the pure solvent. The properties mentioned are colligative, which means: only the number of dissolved particles is decisive, not the chemical nature of the solute. osmotic pressure is another colligative property; it can be calculated using van't Hoff equation and it especially plays an important role in biology.

PhysChemBasics#3 Thermal Equilibrium 101 The conductive transport processes of thermal conductivity and diffusion can be described by similar laws: these are Fourier's laws and Fick's laws. Small and light gas particles show both the largest heat conductivity and diffusion coefficient. While the complete conversion of work into heat is not a problem, the conversion of heat into work is only possible with a certain efficiency; according to Carnot, this efficiency cannot exceed delta (T) / T (high).

The vapor pressure is the equilibrium partial pressure over a condensed phase. The vapor pressure mainly depends on the volatility of the compound and temperature. The vapor pressure curve of a pure substance, which begins at the triple point and ends at the critical point, can be described using Clausius-Clapeyron equation . With a solute present, the vapor pressure is lower than with the pure solvent. Vapor pressure reduction is proportional to the concentration of the solute and described by Raoult s 1st law. When we dissolve a gas in a liquid, the amount of gas dissolved is proportional to the partial pressure of the gas above the liquid - that's Henry's law.