quiz 11/15 Flashcards
what is a phase diagram?
a phase diagram consists of areas separated by lines
what do the areas represent on a phase diagram?
the areas represent ranges of T and P where a single phase is most stable
what do the lines represent on a phase diagram?
the lines represent sets of T and P where two phases are in equilibrium
what happens at the point where 3 lines meet?
it represents one set of T and P values where 3 phases are in equilibrium
what are the lines called on a phase diagram?
phase boundaries or coexistence curves
what happens along the phase boundaries?
two phases are in equilibrium and therefore, their chemical potentials are equal
what is usually on the y-axis on a phase diagram?
P (pressure)
what is usually on the x-axis on a phase diagram?
T (temperature)
any two intensive properties of the system could be used instead. when we consider systems composed of 2+ substances, we’ll see that a _____ ______ is often used on the x-axis
composition variable
example of a composition variable
mole fraction
the liquid and vapor of a pure substance in a closed container. what is the vapor pressure in this example?
the vapor pressure is the pressure of the gas in equilibrium with the liquid
the vapor pressure is the pressure of the gas in equilibrium with the liquid. what would the liquid-vapor phase boundary show?
shows how the vapor pressure varies with temperature
the vapor pressure is the pressure of the gas in equilibrium with the liquid. what would the solid-gas boundary phase show?
shows how the sublimation vapor pressure (the vapor pressure of the solid phase) varies with T
If a liquid in an open container is exposed to an
external pressure equal to its vapor pressure, it
will boil. what are two ways that this can be done?
-raising the temperature of the liquid (raising its vapor pressure)
-reducing the external pressure (in a vacuum chamber)
for bubbles of vapor in the liquid not to collapse under the external pressure, what needs to happen?
the vapor pressure must equal the external pressure
what appears on phase diagrams beyond the end of the liquid-gas phase boundary?
this phase is called a supercritical fluid
what can be used as the definition of an ideal solution?
Raoult’s Law
where does the origin of Raoult’s Law come from?
comes from the vapor pressure lowering effect the solute has on the solvent
how is the ideal solution explained in terms of entropy?
when a solute is present, the solvent’s entropy is higher than in the pure solvent, so there is less entropic advantage in vaporizing to further increase entropy
what does this graph show?
-shows the total and partial pressures of a mixture as a function of the mole fraction of the liquid
-Raoult’s law is obeyed for all values of xA so this is an ideal solution
how does an ideal solution behave?
the vapor pressure of a substance in the gas is directly proportional to its mole fraction in the liquid
how is the vapor pressure for real solutions involving a very dilute solute?
the vapor pressure of the solute is proportional to the mole fraction of the solute in the liquid but not to the vapor pressure of the pure solute
the ____ of mixing is not ideal but the _____ of mixing is ideal
-enthalpy
-entropy
