1.8

Question 1

What is a phase?

Answer 1

sample of matter uniform throughout chemically and physically

Question 2

What is a phase change?

Answer 2

essentially a change in intermolecular distance and freedom of motion. All phase changes are possible under the right conditions

Question 3

true or false, energy changes accompany changes in state of matter

Answer 3

true

Question 4

What is the difference between state and phase?

Answer 4

State of matter is the state of a particular compound in a physical system whereas phase is a set of states within such a system.
( eg. a rubber and crystal in a flask are both solid; different phases, but the same state: solid)

Question 5

Define evaporation

Answer 5

• a surface property
• to do with molecules on the surface being able to overcome the attraction between their neighbors; thus can change from liquid phase to gas phase

Question 6

define vaporization

Answer 6

it is the phase transition of a substance from liquid to gas phase

Question 7

characteristics of evaporation/ vaporization

Answer 7

• need an open system
• vaporization at surface at temperatures below boiling point
• endothermic: cooling process (energy from surroundings must be supplied)
• liquids in open containers evaporate completely

Question 8

Liquid in a closed container what happens?

Answer 8

In a closed container some of the molecules escape from the surface of the liquid to form a gas.
Some gas particles collide with the liquid and return to it; as the space of above the liquid is saturated with water vapor. (vapor pressure remains constant; there is a maximum)

-Eventually rate of evaporation = rate of condensation; the system at this point is said to be in DYNAMIC EQUILIBRIUM

Question 9

What is vapor pressure?

Answer 9

is the pressure of gas (vapor) that collects above the liquid in a closed container at a given temperature

Question 10

Characteristics of vapor pressure

Answer 10

directly related to T (temperature)

inversely related to strength of intermolecular forces (the stronger the intermolecular forces the lower the Vp at a particular T)

Question 11

What are melting points and boiling points indicators of?

Answer 11

strength of intermolecular forces of attraction

Question 12

what is moisture

Answer 12

droplets of water suspended in air

Question 13

How do bubbles form?

Answer 13

bubbles occur because the conversion of liquid to gas does not occur on the surface anymore, but rather within the bulk sample.

• as we heat up the sample some particles do move further apart into gas phase; since gases are less dense than liquid; they float up

Question 14

Boiling why does it occur?

Answer 14

• vapor forms in the interior of the liquid
• boiling depends on the applied pressure; if the temperature at which vapor pressure = external pressure (the bubbles will maintain a constant size);
• to enlarge, the vapor pressure( inside the bubble) must be greater than atmospheric pressure;
• if external pressure is greater than vapor pressure; will push all liquid particles closer together, pushing bubble inwards, preventing boiling to occur

Question 15

When does solid- liquid transition occur, and what do you call that phase change?

Answer 15

Melting

• occurs at melting point
• equilibrium occurs when melting rate= freezing rate

Question 16

When does solid- gas transitions occur, and what is it called?

Answer 16

Sublimation

- occurs at low P and high T (like ideal gas conditions)

Question 17

What are phase diagrams?

Answer 17

the graph shows the effect of pressure and temperature on substance (with phase boundaries)

Question 18

What are phase diagrams used to predict?

Answer 18

• which phase present at a particular temperature and pressure
• the freezing and boiling point at particular pressure
• the phase changes that will occur on changing T or P

Question 19

What do the lines in a phase diagram represent?

Answer 19

phase boundary; shows conditions of T and P where equilibrium exists between phases either side

Question 20

What does it mean by critical point?

Answer 20

conditions which separate liquid and gas phases no longer exist; above this region we cannot distinguish between a liquid and a gas

Question 21

What is the triple point?

Answer 21

three phases in equilibrium

- all phases can exist simultaneously

Question 22

What is supercritical fluid?

Answer 22

a substance which exists above critical point; has properties of both gas and liquid

Question 23

solid to liquid

Answer 23

melting

Question 24

liquid to solid

Answer 24

freezing

Question 25

solid to gas

Answer 25

sublimation

Question 26

gas to solid

Answer 26

deposition

Question 27

liquid to gas

Answer 27

evaporation/ vaporization

Question 28

gas to liquid

Answer 28

condensation