Phase Equilibrium:Single Component

Contributions by:John L. Falconer & Will Medlin

Department of Chemical and Biological EngineeringUniversity of Colorado

Boulder, CO 80309-0424

Supported by the National Science Foundation

The same amount of solid iodine is added to two identical glass tubes, which are sealed and heated to 50°C. The color in both tubes is the same. Each has solid iodine in the bottom. When more iodine crystals are added to one tube, the vapor in that tube _______.

A. becomes darker

B. remains the same

C. becomes lighter

Iodine

50°C

Iodine

50°C

Vapor0.1 mol

Liquid0.9 mol

A piston-cylinder at 45°C and 0.5 bar contains 0.9 mol of hexane liquid and 0.1 mol of hexane vapor in equilibrium. The pressure is doubled at constant temperature by pushing down on the piston. What happens?

A. Most of the vapor condenses

B. All the vapor condenses, the liquidis below its saturation temperature

C. All vapor condenses, the liquid is below its saturation pressure.

D. The system contains only vapor

Vapor0.1 mol

Liquid0.9 mol

A piston-cylinder at 45°C and 0.5 bar contains 0.9 mol of hexane liquid and 0.1 mol of hexane vapor in equilibrium. Weights are removed from the piston to decrease the pressure to half its original value at constant temperature. What happens?

A. Most of the liquid evaporates

B. The liquid all evaporates, the vapor is above its saturation pressure

C. The liquid all evaporates, the vapor is above its saturation temperature

D. The system contains only liquid

Vapor0.1 mol

Liquid0.9 mol

A piston-cylinder at 45°C and 0.5 bar contains 0.9 mol of hexane liquid and 0.1 mol of hexane vapor in equilibrium. The temperature is lowered to 40°C at constant pressure.What happens?

A. Some of the vapor condenses

B. The vapor all condenses, the liquidis below its saturation temperature

C. The vapor all condenses, the liquidis below its saturation pressure

D. The system contains only liquid

1 kg

CH4

Vapor

10 bar300 K

Methane gas at 10 bar and 300 K is in a piston-cylinder. If more and more weight is added to the system, what eventually happens?

A. Gas becomes more dense

B. Some liquid forms

C. All the vapor becomes liquid

D. All the vapor becomes solid

Vapor0.2 mol

Liquid0.5 mol

A piston-cylinder at 45°C and 0.5 bar contains 0.5 mol of hexane liquid and 0.2 mol of hexane vapor in equilibrium. What happens when 0.1 mol hexane vapor is removed at constant pressure and temperature?

A. Some of the liquid evaporates

B. All of the liquid evaporates

C. No liquid evaporates

D. Some vapor condenses

E. All of the vapor condenses

1 kg0.1 mol vapor

Vapor0.1 mol

Liquid0.9 mol

A fixed-volume container at 45°C and 0.5 bar contains 0.9 mol of hexane liquid and 0.1 mol of hexane vapor in equilibrium. The temperature is lowered to 40°C. What happens? A. Some of the vapor condenses

B. All of the vapor condenses

C. Some of the liquid evaporates

D. All of the liquid evaporates

A fixed-volume container at 45°C contains 1 L of liquid benzene and 1 L of benzene vapor in equilibrium. If 0.4 L liquid benzene is removed and the container is at constant temperature and volume, the pressure ____________.

A. increases

B. decreases

C. remains the same

D. Not enough information. Liquid1 L

Vapor1 L

0.4 Lliquid

A fixed-volume container at 45°C contains 1 L of liquid benzene and 1 L of benzene vapor and air in equilibrium. If 0.4 L liquid benzene is removed and the container is at constant temperature and volume, the total pressure ____________.

A. increases

B. decreases

C. remains the same

D. Not enough information.

Liquid1 L

Vapor1 L

0.4 Lliquid

A fixed-volume container at 45°C contains 1 L of liquid benzene and 1 L of benzene vapor in equilibrium. If 0.4 L liquid benzene is removed and the container is at constant temperature and volume, then in the container, ___________________.

A. some liquid evaporates

B. some vapor condenses

C. the amount of vapor does not change

Liquid1 L

Vapor1 L

0.4 Lliquid

A fixed-volume container at 45°C contains 1 L of liquid benzene and 1 L of benzene vapor and air in equilibrium. If 0.4 L liquid benzene is removed and the container is at constant temperature and volume, then in the container, ___________________.

A. some liquid evaporates

B. some vapor condenses

C. the amount of vapor does not change

Liquid1 L

Vapor1 L

0.4 Lliquid

Vapor0.1 mol

Liquid5 mol

A fixed-volume container at 45°C contains 5 mol hexane liquid and 0.1 mol hexane vapor in equilibrium. An additional 0.2 mol of hexane vapor are added, while keeping the temperature constant. What happens?

A. Some of the added vapor condenses

B. All the added vapor condenses

C. Some of the liquid evaporates

D. All of the liquid evaporates

0.2 mol vapor

Vapor0.1 mol

Liquid5 mol

A fixed-volume container at 45°C contains 5 mol hexane liquid and 0.1 mol hexane vapor in equilibrium. An additional 0.2 mol of hexane vapor are added, while keeping the temperature constant. The pressure ___________.

A. increases

B. decreases

C. remains the same

0.2 mol vapor

Vapor0.1 mol

Liquid0.5 mol

A fixed-volume container at 45°C contains 0.5 mol of hexane liquid and 0.1 mol of hexane vapor in equilibrium. What happens when 0.2 mol hexane vapor is added at constant temperature?

A. Some of the added vapor condenses

B. The liquid all evaporates

C. Most of the liquid evaporates

D. All the added vapor condenses

E. All the added vapor and some original vapor condenses

0.2 mol vapor

Vapor0.2 mol

Liquid0.5 mol

A piston-cylinder at 45°C and 0.5 bar contains 0.5 mol of hexane liquid and 0.2 mol of hexane vapor in equilibrium. What happens when 0.1 mol hexane vapor is removed at constant temperature?

A. Some of the liquid evaporates

B. All of the liquid evaporates

C. No liquid evaporates

D. Some vapor condenses

E. All of the vapor condenses 45°C

0.1 mol vapor

CO2 solid and vapor are in equilibrium at -70°C and 0.2 MPa in a piston/cylinder. The pressure increasesto 0.3 MPa at -70°C. What happens?

A. Some vapor condenses

B. All the vapor condenses

C. Some solid sublimes

D. All the solid sublimesCO2

Vapor

CO2

Solid

A piston-cylinder at 45°C and 0.5 bar contains hexane in VLE. You push down on the piston until the vapor volume is half its original volume. The system is at constant temperature. What is the pressure at the new equilibrium?

A. 0.25 bar

B. 0.5 bar

C. 1.0 bar

D. Cannot be determined

HexaneVapor

HexaneLiquid

A piston-cylinder at 45°C and below atmospheric pressure contains 0.9 mol of hexane liquid and 0.1 mol of hexane vapor in equilibrium. Weights areremoved from the piston to decrease the pressure to 99% of its original value at constant temperature.What happens?

A. Some of the liquid evaporates

B. Most of the liquid evaporates

C. All the liquid evaporates

D. All the vapor condenses

E. Some of the vapor condenses

0.1 molVapor

0.9 molLiquid

Pure CO2 is in solid‐vapor equilibrium in a piston-cylinder at 1 bar. On a molar basis, 50% of the CO2 is in the solid phase, but the solid occupies only 5% of the volume. If the volume of the container is decreased to half its value by pushing down on the piston at constant T, what will be the final pressure of the system?

A. 1 bar

B. 2 bar

C. A little less than 2 bar

D. A little more than 2 bar Solid50% CO2

V1 ½ V1

T1 T1

P

V

System

x

0.7 0.3

For this single component P-V diagram, what is thefraction of the material that is liquid?

A. 0.3

B. 0.7

C. 3/7 th

Which statement about the diagram is not true?

A. Components 1 and 2 have attractive interactions

B. A liquid at the azeotrope composition boils at constant temperature

C. Activity coefficients < 1

D. Since P1sat > P2

sat , the gas is enriched in component 1

E. Distillation cannot be used to obtain a pure material x1, y1

P

Azeotrope

0 0.5 1.0

P-x1

P-y1

Pure benzene is cooled from 10 torr and 26°C to10 torr and -30°C. Which line represents the pathway that will be followed?

Temperature (°C)

Ben

zene

par

tial

pre

ssur

e (to

rr)

LiquidSolid

Vapor

1

10

100

1000

-40 -20 0 20 40

Starting point

A

B

Benzene in air is cooled from 760 torr and 26°C to 760 torr and -30°C. The plot represents the benzene partial pressure. Which line represents the pathway that will be followed?

Temperature (°C)

Ben

zene

par

tial

pre

ssur

e (to

rr)

LiquidSolid

Vapor

1

10

100

1000

-40 -20 0 20 40

Starting point

A

B

Consider octane in VLE in a container of fixed volume. As the temperature increases, ___________.

A. all the liquid evaporates

B. all the gas condenses

C. the difference between liquid and vapor disappears,

D. either A or C can occur

E. A, B, or C can occurP

ln (V)

A stream containing wet steam (96% vapor, 4% entrained liquid) mixes with a N2 stream. Both streams are at 1 bar and 100°C. After mixing, the temperature ________________.

A. increases

B. decreases

C. remains the same

Steam

N2

1 L of liquid ethanol is added to a 5 L container and also to a 10 L container. Both containers are at the same temperature, and both have only ethanol in them. Which is true at equilibrium ?

A. PI < PII

B. PI = PII

C. PI > PII

I

II

1 L of ethanol(l) is added to a 5 L container and to a 10 L container. The volumes of the containers are fixed and at room temperature. If the containers only contain ethanol, the pressure in the 10 L container is _________ in the 5 L container.

A. greater than

B. lesser than

C. the same as

D. half the pressure

5 L

10 L

1 L of ethanol(l) is added to a 5 L container and to a 10 L container. The volumes of the containers are fixed and at room temperature. If the containers only contain ethanol, it is in ___________in both containers.

A. a liquid phase

B. a vapor phase

C. both a liquid and vapor phase

D. None of the above.

5 L

10 L

Liquid ethanol becomes a solid when the pressure increases isothermally. The Gibbs free energy of the ethanol ____________.

A. increases

B. decreases

C. remains the same

Ethanol starts as a vapor. Both its temperature and pressure are below the triple point. At constant temperature, you raise the pressure. What phases do you see as you increase pressure?

A. Gas Liquid Solid

B. Gas Liquid

C. Gas Solid

D. Gas Solid Liquid

A can of office duster (used for cleaning cameras and keyboards) contains a liquid-vapor mixture of 1,1,1,2-tetrafluoroethane (TFE). If the container is used continuously by depressing the nozzle, the flow rate of air ______________________________ .

A. decreases because the amount of TFE decreases

B. decreases because the temperature decreases

C. remains constant until all the liquid is used up

D. remains constant and then decreases

Why does water have a higher boiling point than cyclohexane?

A. Water takes up less space

B. Water experiences stronger intermolecular interactions

C. Water has a lower molecular weight

The square well potential for two molecules is shown. Compared to molecule 2, molecule 1 is ________ and has _________ intermolecular interactions.

A. larger; stronger

B. smaller; stronger

C. larger; weaker

D. smaller; weaker

r u(r)

1 2