Phase Changes and Thermodynamics

Question 1

Is the change in enthalpy positive or negative for vaporization?

Answer 1

positive enthalpy change

Question 2

Define melting

Answer 2

solid to liquid

Question 3

Is the change in entropy positive or negative for vaporization?

Answer 3

positive entropy change

Question 4

 The balance between enthalpy and entropy is controlled by?

Answer 4

temperature

Question 5

 At any given temperature the most stable phase is the substance with?

Answer 5

the lowest free energy

Question 6

What phase are most substances in at high temps?

Answer 6

gases

Question 7

Is the change in enthalpy positive or negative for condensation?

Answer 7

negative enthalpy change

Question 8

Is the change in entropy positive or negative for condensation?

Answer 8

negative entropy change

Question 9

What does the entropy tell us?

Answer 9

 The entropy tells us about the number of potential microstates for distributing energy
• The higher the entropy, the more likely such a state is to randomly occur

Question 10

Describe the relationship between entropy and phases

Answer 10

• Solids are low in entropy and gases are high in entropy

Question 11

What is the Gibbs Free Energy Formula?

Answer 11

G = H - TS

Question 12

Is the change in entropy positive or negative for sublimation?

Answer 12

positive entropy change

Question 13

Describe the relationship between enthalpy and molecular distance

Answer 13

 The enthalpy of two molecules in close proximity is lower than two molecules separated by some distance

Question 14

What always leads to a lower overall free energy?

Answer 14

spontaneous chanes

Question 15

Define sublimation

Answer 15

solid to gas

Question 16

Describe the relationship between entropy and number of molecules

Answer 16

 Entropy increases with increasing the number of molecules

Question 17

At high temps does enthalpy or entropy dominate?

Answer 17

entropy

Question 18

Define vaporization

Answer 18

liquid to gas

Question 19

Describe the relationship between entropy and temperature

Answer 19

 Entropy increases with increasing temperature

Question 20

What is it mean when G = 0?

Answer 20

the system has reached equilibrium

Question 21

Is the change in entropy positive or negative for deposition?

Answer 21

negative entropy change

Question 22

Is the change in entropy positive or negative for melting?

Answer 22

positive entropy change

Question 23

Define freezing

Answer 23

liquid to solid

Question 24

What phase are most substances in at low temps?

Answer 24

solids

Question 25

Is the change in enthalpy positive or negative for melting?

Answer 25

positive enthalpy change

Question 26

Describe the relationship between enthalpy and phases

Answer 26

The lowest enthalpy phase is the solid phase and the highest is the gas phase

Question 27

Is the change in entropy positive or negative for freezing?

Answer 27

negative entropy change

Question 28

Describe the relationship between entropy and volume

Answer 28

 Entropy increases with increasing volume

Question 29

Does the universe tend toward higher or lower entropy?

Answer 29

higher

Question 30

Define deposition

Answer 30

gas to solid

Question 31

Define condensation

Answer 31

gas to liquid

Question 32

Does the universe tend toward higher or lower enthalpy?

Answer 32

lower

Question 33

At low temps does enthalpy or entropy dominate?

Answer 33

enthalpy

Question 34

Is the change in enthalpy positive or negative for freezing?

Answer 34

negative enthalpy change

Question 35

Is the change in enthalpy positive or negative for deposition?

Answer 35

negative enthalpy change

Question 36

Is the change in enthalpy positive or negative for sublimation?

Answer 36

positive enthalpy change