Simple Mixtures Flashcards
(T/F): For a system with more than one component, we can define molar quantity for each component.
False. We can define PARTIAL molar quantity for each component
Formula for partial molar volume.
Vi = ( change V/ change ni) at constant T, P, nj
Define partial molar volume
Change in volume of mixture when small amount of i is added, holding other variables constant
Illustrate partial molar volume through binary system of water and ethanol.
Adding 1mol of water to 1 vat of water will result of 18mL increase in volume which is same as the molar volume of pure water
Adding 1 mol of ethanol to same vat of water will result to 54 mL increase in volume which is less than the molar volume of pure ethanol (58 mL)
The partial molar volume of ethanol is 54 mL
Molar quantities are not ____ but partial molar quantities are.
explicitly additive
Change in molar volume (dV) is equal to?
summation of product of partial molar volume and change in the number of moles of each component
dV = E Vi dni
Define chemical potential.
It is the measure of?
In a mixture, the chemical potential is the change in Gibbs free energy (spontaneity) of the system when small amounts of i is added to it, with other variables held constant
It is the measure of tendency of substances to transform or escape.
The chemical potential must be ___ throughout the system because of its ___ property
the same; intensive
Chemical potential is also known as the?
Molar Gibbs energy
In a single component with more than one phases, the change in Gibbs free energy is equal to?
Summation of product of chemical potential and change in number of moles of each phases.
In an isolated system with two phases, change in G is?
dG =[chem po (a)-chem po (b)] dni (a)
What will happen to amount of i in phase b (and the sign) if the chemical potential of i in phase a is greater than the phase b? What is the direction of i?
increase; positive
moves from phase a toward phase b
(from higher chemical potential to lower)
(T/F). Movement of amount of i will continue until dG becomes constant.
False. until dG becomes zero.
(molar) Gibbs free energy of an ideal gas with temperature and pressure
dG = V dP - S dT
dGm = Vm dP - Sm dT
Chemical potential of ideal gas
m = mu (T) + RT ln P
chem po = stand. chem po at temp T + RT ln P
Ideal solution is defined as solution that obeys ____ over the ____.
Raoult’s Law; entire range of concentration.
What is Raoult’s Law?
Vapor pressure over a solution is dependent on the mole fraction of the volatile component in the solution.
Lowering vapor pressure of a volatile liquid due to presence of solute
The vapor pressure exerted by a solution in which the solvent is volatile and solute is involatile is? ( in terms of molar fraction of solvent and solute)
Pi = xi Pi*
vapor pressure by solution = molar fraction of volatile solvent * vapor pressure by pure solvent
In terms of involatile solute:
Pi = Pi* (1-xj)
Vapor pressure of the volatile component in a solution is always ___ its vapor pressure as a pure liquid.
less than
What is the chemical potential of a volatile component in solution?
mu i (sol’n) = mu i* + RT ln xi
chemical potential of solution = chemical potential of pure liquid + RT ln molar fraction
Properties of solution that depend only on the amount of involatile solute in solution
Colligative Properties
Colligative properties do not depend on the nature of solute but only on?
… however?
the number of solute molecules relative to the total number of molecules present (solute mole fraction)
Vapor pressure decrease depends on solvent mole fraction.
Hence, colligative properties actually depend on the relative amount of volatile component in the solution
Form of Gibbs-Helmholtz equation for melting point depression
d(∆G/T)/dT = -∆H/T^2
∆G=T∆H-∆S
Mathematical expression for melting point depression and what it implies?
1/T = 1/T0 - R ln xi / ∆Hfusion
T0 = melting point of pure solvent
T = melting point of solution
: mp of solution is always less than mp of pure solvent
MP expression when solution is very dilute
T = T0 - Kf m
Kf = cryoscopic constant
Kf = -MRT0^2 / ∆Hfusion
BP elevation expression and what it implies?
1/T = 1/T0 + R ln xi / ∆Hvaporization
T0 = bp of pure solvent
T = bp of solution
: BP of solution is always greater than BP of pure solvent
BP expression in terms of molal concentration of solute
T = T0 + Kb m
Kb = MRT0^2 / ∆Hvaporization
If a pure solvent is separated from its solution by a membrane permeable only to the solvent, _____
the solvent molecules will move through the membrane to establish equilibrium
tendency (chemical potential) is for matter to move from
higher chem po to lower chem po
Pressure required to stop or reverse the movement of matter
osmotic pressure
To achieve equilibrium, the solvent must exert ___ as that of solvent
same pressure
molar fraction, xj = ?
nj / nj + ni
osmotic pressure in terms of molar concentration of solute
osmotic pressure = cj RT
cj = nj / Vsolution
