Normality and Titration*footnote1
| Definition of Normality: | NA = [#H+, #OH- or #e - ] CA |
| Use for Titration: | N1V1 = N2 V 2 |
| Definition of molar heat capacity: | q = Cn ΔT |
| First Law of Thermodynamics: | ΔE = q + w |
| Definition of enthalpy: | ΔH = ΔE + PΔV |
| Definition of Gibbs' free energy : | ΔG = ΔH - TΔS |
| Obtaining the ΔrHo from ΔHof : | ΔrHo = νΔH
of products - |
| Obtaining the ΔrSo from So : | ΔrSo = νSo
products - νSo reactants (for ions these are ΔSo) |
| Condition | For an Isolated System | For a Closed System at Constant Pressure |
| Spontaneous Process | ΔS > 0 | ΔG < 0 |
| Equilibrium | ΔS = 0 | ΔG = 0 |
| Non spontaneous Process | Impossible | ΔG > 0 |
The equilibrium constant from thermodynamic data:
K = e-Δ Go/RT (very important)
The van't Hoff plot uses the linearized version of this equation in the form:
ln K = - (ΔHo/R)(1/T) + ( ΔSo/R)
i.e
y = m x + b
Where the slope, m, is: m = -(ΔHo/R
) (NOTE NEGATIVE!)
and the intercept, b, is: b = (ΔSo/
R)
where x is:
x = (1/T)
and y is:
y = ln K
Definitions of some Ks
Ksp is the equilibrium constant between a slightly soluble ionic compound (reactant) and its ions in solution (product). Example:
CaF2 <--> Ca2+ + 2F-
Ksp = [Ca2+][F- ]2
Kd is the equilibrium constant of a complex ion (in a Lewis acid-base reaction) with its dissociated simple ion and ligands. Example:
Co(NH3)62+ <--> Co2+ + 6NH3
Kd = [Co2+
] [NH3]6
[Co(NH3)62+]
p function: p( ) = -log10( )
Examples:
pH = -log [H3O+]
pOH = -log[OH-]
pCl = -log[Cl-]
pKa = -log Ka
Zero order kinetics:
rate equation:
-ΔC/Δt = k
integrated rate equation: C = -kt + Co
First order kinetics:
rate equation:
- ΔC/Δt = kC
integrated rate equation: lnC = - kt + lnCo
Second order kinetics:
rate equation:
- ΔC/Δt = kC2
integrated rate equation: 1/C = kt + 1/Co
Arrhenius equation:
k = A e-ΔH*/RT
where ΔH* is the "activation energy" or "enthalpy of activation"
Equations on Electrochemistry:
In the stoichiometry of the electrochemical cell, one can convert from coulombs to moles of electrons using the Faraday constant, F. F = 96 487 C mol-1
Cell diagram:
Anode | Anolyte | (salt bridge) | Catholyte | Cathode
OXIDATION
REDUCTION
Standard Potentials, Eo, are reduction potentials
Eocell = Eooxidation, anode + Eocathode
Eooxidation = -E ostd
Eoreduction = + Eo std
For non-standard conditions:
Nernst Equation:
Ecell = Eo cell - (RT/nF) lnQ n is the number of electrons transferred
Ecell = Eo cell - (0.0592/n) lnQ at 25oC
The relationship between Gibbs' free energy and potential:
ΔG = - nFE
*footnote 1: SIO and IUPAC have recommended elimination of normality. Thus, the algebraic symbol, N, and the unit symbol, N, are not standard SI. I disagree with this decision which was was based upon the understanding the normality is a convenience and not a necessity. The real reason for the use of normality is if one has a totally unknown substance when doing a titration, in which case the answer can be reported only in normality (or something equivalent.) The convenience of the equation: N1V1 = N 2V2 is only a side issue.