quiz 11/15

Question 1

what is a phase diagram?

Answer 1

a phase diagram consists of areas separated by lines

Question 2

what do the areas represent on a phase diagram?

Answer 2

the areas represent ranges of T and P where a single phase is most stable

Question 3

what do the lines represent on a phase diagram?

Answer 3

the lines represent sets of T and P where two phases are in equilibrium

Question 4

what happens at the point where 3 lines meet?

Answer 4

it represents one set of T and P values where 3 phases are in equilibrium

Question 5

what are the lines called on a phase diagram?

Answer 5

phase boundaries or coexistence curves

Question 6

what happens along the phase boundaries?

Answer 6

two phases are in equilibrium and therefore, their chemical potentials are equal

Question 7

what is usually on the y-axis on a phase diagram?

Answer 7

P (pressure)

Question 8

what is usually on the x-axis on a phase diagram?

Answer 8

T (temperature)

Question 9

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

Answer 9

composition variable

Question 10

example of a composition variable

Answer 10

mole fraction

Question 11

the liquid and vapor of a pure substance in a closed container. what is the vapor pressure in this example?

Answer 11

the vapor pressure is the pressure of the gas in equilibrium with the liquid

Question 12

the vapor pressure is the pressure of the gas in equilibrium with the liquid. what would the liquid-vapor phase boundary show?

Answer 12

shows how the vapor pressure varies with temperature

Question 13

the vapor pressure is the pressure of the gas in equilibrium with the liquid. what would the solid-gas boundary phase show?

Answer 13

shows how the sublimation vapor pressure (the vapor pressure of the solid phase) varies with T

Question 14

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?

Answer 14

-raising the temperature of the liquid (raising its vapor pressure)
-reducing the external pressure (in a vacuum chamber)

Question 15

for bubbles of vapor in the liquid not to collapse under the external pressure, what needs to happen?

Answer 15

the vapor pressure must equal the external pressure

Question 16

what appears on phase diagrams beyond the end of the liquid-gas phase boundary?

Answer 16

this phase is called a supercritical fluid

Question 17

what can be used as the definition of an ideal solution?

Answer 17

Raoult’s Law

Question 18

where does the origin of Raoult’s Law come from?

Answer 18

comes from the vapor pressure lowering effect the solute has on the solvent

Question 19

how is the ideal solution explained in terms of entropy?

Answer 19

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

Question 20

what does this graph show?

Answer 20

-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

Question 21

how does an ideal solution behave?

Answer 21

the vapor pressure of a substance in the gas is directly proportional to its mole fraction in the liquid

Question 22

how is the vapor pressure for real solutions involving a very dilute solute?

Answer 22

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

Question 23

the ____ of mixing is not ideal but the _____ of mixing is ideal

Answer 23

-enthalpy
-entropy