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EGEE 441: Electrochemistry L1
N/A
47
Chemistry
Undergraduate 4
10/24/2012

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Term
in weak electrolytes, there is an equilibrium between __ and __
Definition
partially dissociated molecules

ions
Term
Is pure water an electrolyte solution?
Definition
no
Term
define molality
Definition
(mol solute)/(kg solvent)
Term
define molarity
Definition
(mol solute)/(mol solvent)
Term
can molality be defined for a solvent?
Definition
no
Term
can molarity be defined for a solvent?
Definition
no
Term
what is the molarity of water?
Definition
55.51 mol/kg
Term
for equilibrium electrochemistry, should you use molality or molarity?
Definition
molality
Term
at ambient conditions, how are molarity (c) and molality (b) related?
Definition
c=b*ρ
Term
which of the following depend on T and P?
molality, molarity, mole fraction, mass fraction, volume fraction, percent
Definition
molarity and volume fraction
Term
what is the equation for chemical potential for an ideal solution?
Definition
μ = μ^o + RTln(x)
Term
for the chemical potential eqn, do the terms depend on concentration?
Definition
standard state term: no

log term: yes
Term
for the chemical potential eqn, do the terms depend on the concentration scale?
Definition
standard state term: yes
log term: yes
Term
does the chemical potential depend on the concentration scale?
Definition
no
Term
the chemical potential is a function of __, __, and __
Definition
T
P

composition
Term
for electrolyte solutions, molality should be used in all cases, except __ and __
Definition
electrolyte conductivity
electrochemical kinetics
Term
μ^(o,x) is standard chemical potential on the __ concentration scale
Definition
molar fraction
Term
μ^(o,b) is standard chemical potential on the __ concentration scale
Definition
molal
Term
what is the relationship between molar fraction (x) and molality (b)?
Definition
x = b/(b + 55.51)
Term
define chemical potential, μ
Definition
a form of potential energy that can be absorbed or released during a chemical reaction
Term
define activity, a
Definition
effective concentration of a solute for the purposes of mass action
Term
define activity coefficient, γ
Definition
a factor used in thermodynamics to account for deviations from ideal behavior in a mixture of chemical substances
Term
what is the relationship between γ^x and γ^b?
Definition
???
Term
what is the unit of chemical potential?
Definition
J/mol
Term
what are the units of activity and activity coefficient?
Definition
dimensionless
Term
for a dilute electrolyte solution, x and γ^x of water are close to __
Definition
1
Term
For a dilute electrolyte solution, chemical potential μ of water is close to __. Why?
Definition
standard chemical potential (μ^o) of water

because x and γ^x are close to 1
Term
for electrolyte solutions, μ is a sum of what contributions?
Definition
the anion and cation contributions

μ = (ν^+)(μ^+) + (ν^-)(μ^-)
Term
when I -> 0, ab -> ? and γb -> ?
Definition
ab -> b γb -> 1
Term
what is the physical meaning of the activity coeff.?
Definition
it shows the difference between the chemical potential of the ith species in real vs. ideal solutions
Term
can the activity coeff. of an ion be experimentally measured?
Definition
no
Term
can the activity coeff. of an ion be theoretically calculated?
Definition
yes, for a dilute solution
Term
can the activity coeff. of an electrolyte be experimentally measured?
Definition
yes
Term
for a strong electrolyte, how is the mean activity coeff. γ related to the anion and cation activity coeff's γ- and γ+?
Definition
it is approximately equal to both
(γ = γ- = γ+)
Term
the activity coefficient of the anion and cation are usually __
Definition
different
(only approx. equal for a strong electrolyte)
Term
are the absolute values of standard chemical potentials known?
Definition
no
Term
Gibbs energy of formation can be found __
Definition
experimentally
Term
Debye-Huckel theory provides a method to calculate what?
Definition
the activity coefficient of a single ion surrounded by an ionic atmosphere
Term
does the mean activity coeff. depend on concentration?
Definition
yes, strongly
Term
at high concentrations, the mean activity coeff. can be __
Definition
above 1
Term
the total concentration of a weak electrolyte is a sum of what?
Definition
the concentration of the dissociated ions and
the concentration of the undissociated molecules
Term
what is the equation for pH?
Definition
pH = -log[H+]
or [H+] = 10^(-pH)
Term
what is the activity of water in pure water?
Definition
1
but it can deviate in highly concentrated solutions
Term
at 25 C and 1 bar, what is the pH of pure water?
Definition
7
Term
pH is hard to define in what kind of solutions?
Definition
highly concentrated solutions
Term
what are the 2 main problems in defining pH?
Definition
1. pH is a thermodynamic characteristic of an individual ion, so assumptions must be made to find it
2. commercially available pH probes are not usable in all environments
Term
define buffer solution
Definition
solution made of a weak acid and salt or a weak base and salt, which resists changing pH upon small additions of acid or base
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