7.8. Multiatomic systems

Question 1

What is Boltzmann’s definition of entropy?

Answer 1

A measure of the number of ways how microstates in a system in thermodynamic equilibrium can produce the same macrostate

Question 2

What are the 4 things assumed by the kinetic gas theory?

Answer 2

1. Size of molecules is very small compared to distance between them
2. Follow random thermal motion
3. Molecules frequently collide with each other and with the walls of the container
4. The entire fluid can move in ordered motion (flow)

Question 3

What does the kinetic gas theory mean for Ekin?

Answer 3

Temperature is directly proportional to the average Ekin of particles (Ekin = 3/2 kT)

Question 4

What is the Maxwell-Boltzmann velocity distribution?

Answer 4

• Talks about the distribution of speed of gaseous particles for different T
• graph : number of molecules vs speed

Question 5

Which rules does an ideal gas follow? (4)

Answer 5

1. Gas molecules are chemically pure and identical
2. Molecules are apporximated as points with no volume
3. Unpredictable movement but still follow’s newton’s second law
4. If they collide, it is only elastic collision (no loss of Ekin)

Question 6

Newton’s second law of motion

Answer 6

acceleration depends on force acting upon an object and mass of object F=ma

Question 7

What is the unit of the boltzman constant?

Answer 7

j/k (same as entropy)

Question 8

What is a real gas?

Answer 8

molecules occupy a space, ad have interactions with each other + inelastic collisions

Question 9

In the state equation, what is the constant “a” for?

Answer 9

correction for the intermolecular forces

Question 10

In the state equation, what is the constant “b” for?

Answer 10

correction for the molecular size. its value is the volume of 1mol of the atoms/molecules

Question 11

What is the Boltzmann factor?

Answer 11

probability of a state of energy relative to the probability of another state of energy (usually 0)

Question 12

What is the barometric formula?

Answer 12

atmospheric density decreases with altitude

Question 13

What is the potential energy for a particle in a voltage difference of U?

Answer 13

Epot = q * U

Question 14

What is the Nernst equation?

Answer 14

concentration of charged particles at 2 different points

Question 15

What is the equilibrium constant?

Answer 15

the ratio of the reaction rates :

K = e^(-dE/kT)

Question 16

What is the Arrhenius plot?

Answer 16

temperature dependence of equilibrium constant

logK / 1/T

Question 17

How does the conductivity of semi-conductors relate to the Boltzmann distribution?

Answer 17

delocalized electrons of orbitals in metal behave similar to gas particles. In order for e- to escape from cloud, a certain amount of energy must be applied : W

Question 18

What is short range order?

Answer 18

only a fraction of particles is bound by interaction

Question 19

What is the crystalline state?

Answer 19

a solid composed of atoms (ions or molecules) arranged in long range order

Question 20

What are the 4 main properties of the ideal crystal lattice?

Answer 20

1. Anisotropic
2. Stiff (mechanically stable)
3. Defined in volume and shape
4. long range order

Question 21

What is a unit cell?

Answer 21

smallest repeating unit having the full symmetry of the crystal structure

Question 22

What is the lattice point?

Answer 22

points in space about which the particles are free to vibrate in a crystal

Question 23

What are point defects?

Answer 23

occur arround a single lattice point

Question 24

What are the types of point defects? (3)

Answer 24

• vacancy
• doping (foreign particle)
• interstitium (extra atom)

Question 25

What are surface defects?

Answer 25

boundaries that separate different regions in a crystal, each region having same structure but different orientations

Question 26

What is a thermotropic liquid crystal?

Answer 26

order of the structure depends on T : distance of the ordered layers is T dependent

Question 27

What is a lyotropic liquid crystal?

Answer 27

order of the structure is dependant on the ratios of the concentration of their components

Question 28

Why do energy bands “form” in crystals?

Answer 28

because the system tries to avoid having identical quantum states in a crystal structure

Question 29

What is the purpose of doping a semiconductor?

Answer 29

incorporation of a second component into the crystal lattice to reduce Egap. Increase number of thermally excited charge carriers

Question 30

What is an n-type doped semiconductor?

Answer 30

5 valence e-, electron acts as charge carrier : during thermal excitation electron from donor level moves to conduction band

Question 31

What allows conductivity in p-types?

Answer 31

vacancy in the valence band due to acceptor in donor level

Question 32

What is a semi-conductor diode?

Answer 32

a crystalline piece of semiconductor material with a p-n junction connected to 2 electrical terminals

Question 33

What is the most important part of the semiconductor diode?

Answer 33

1 direction conductivity

Question 34

What is the liquid crystal state?

Answer 34

substance that has both liquid and crystal properties

Question 35

What are the 5 main properties of liquid crystals?

Answer 35

1. isotropic
2. deformable
3. takes shape of container
4. defined in volume
5. short range order

Question 36

What is an electro-optical phenomenon in liquid crystalline systems?

Answer 36

change in molecular orientation by electric fields can change the optical transmission properties of the layer

Question 37

What is a thermo-optical phenomenon in liquid crystalline systems?

Answer 37

change in temperature changes helix and thus thickness of crystal, changing the crystal’s color.