Quiz 1

Question 1

What is the first law of thermodynamics?

Answer 1

Energy is conserved , in any process energy can neither be created or destroyed

Question 2

What is an open system?

Answer 2

heat and matter exchange with the surroundings

Question 3

What is a closed system?

Answer 3

only heat exchanges with the surroundings

Question 4

What is an isolated system?

Answer 4

no heat or matter exchange with the surroundings

Question 5

What are heat and work (general)

Answer 5

• different means energy is transferred in and out of a system

Question 6

How does heat transfer energy?

Answer 6

due to temperature changes between system and surroundings

Question 7

How does work transfer energy?

Answer 7

due to unbalanced forces between system and surroundings

Question 8

How is the change in internal energy defined?

Answer 8

sum of heat transferred and work done is internal energy

Question 9

What is a state function?

Answer 9

• depends only on the difference between initial and final STATES, not the path
• internal energy, enthalpy

Question 10

What is a path function?

Answer 10

• processes that transform one state into another
• work and heat, a system does not contain work or heat but rather these are processes that transform one state into another

Question 11

What is an intensive quantity?

Answer 11

• doesnt depend on the amount of substance present
• temperature
• pressure

Question 12

What is an extensive quantity?

Answer 12

• depends on the amount of the substance present
• mass, internal energy

Question 13

What molecular level properties determine C?

Answer 13

• at constant volume, C depends on internal energy
• U in turn depends on the degrees of freedom a given molecule/substance has (translation, rotation, vibration)

Question 14

Heat capacity units

Answer 14

(J/K) extensive quantity

Question 15

Molar heat capacity

Answer 15

(J/K mol) intensive quantity

Question 16

Specific heat capacity

Answer 16

(J/ K g) heat capacity per mass

Question 17

What is the equipartition theorem?

Answer 17

• every quadratic term to the energy is equal to 1/2RT

Question 18

Apply Equipartition theorem to the oscillator.

Answer 18

Etotal = E kin + E pot
Etotal = RT

Question 19

Heat capacity of Monatomic Ideal gases

Answer 19

Cvm = 3/2 R

Question 20

Heat capacity of diatomic ideal gases

Answer 20

• Equipartition theorem predicts
  C = 7/2 R
• However the vibrational mode is not significantly populated at room temperature so C = 5/2 R

Question 21

What does large heat capacity indicate?

Answer 21

A lot of heat is required to change the temperature

Question 22

What is the heat capacity equation?

Answer 22

dq = C dt
q = C(T2- T1)

Question 23

Heat capacity of simple solids

Answer 23

C = 3R

Question 24

Why does the equipartition theorem only work at high temperature?

Answer 24

• the underlying assumption is that the total energy is equally spread over all modes
• that is not correct at low temperatures because the solids follow the laws of quantum mechanics
• only in the limit of high temperature is the classical limit approached

Question 25

How does heat capacity change with temperature?

Answer 25

- Heat capacity decreases at decreasing temperature - At low temperature, high frequency mode of vibration does not contribute to the total energy of the solid, thereby explaining the decay of C with low temperature

Question 26

What factors affect the heat capacity of complex solids?

Answer 26

- increase with molar mass (more vibrational and rotational modes are available), also heavy atoms give rise to low-energy vibrations - liquids have greater heat capacities at the melting temperature than corresponding solids - more flexible molecules have high heat capacities than more rigid molecules - general trend of C increasing w temp

Question 27

Why is Cp larger than Cv?

Answer 27

because not only do we increase the temp when we add heat, we also do pressure volume work against the atmospheric pressure

Question 28

What is the relationship between Cp and Cv ideal gas?

Answer 28

Cp = Cv + nR

Question 29

What is the enthalpy equation?

Answer 29

H = U + PV

Question 30

When is the change in enthalpy equal to the heat transferred at constant pressure? delta H = Qp

Answer 30

- no additional work other than pV work (no electrical work) - the process must be carried out reversibly

Question 31

What is the irreversible, isothermal expansion of an ideal gas?

Answer 31

- sudden removal of weight w = - pex (vf- vi)

Question 32

What is the reversible isothermal expansion of an ideal gas?

Answer 32

- we remove infinitiesimally small amounts of sand in a stepwise manner so that pex = pgas wr = -nRT ln(V2/V1)

Question 33

Derive enthalpy equation

Answer 33

H = U + pV dH = dU + Vdp + pdV at constant pressure dp = 0 dH = dU + pdV

Question 34

Positive work

Answer 34

surroundings are doing work on the system

Question 35

Negative work

Answer 35

system doing work on the surroundings

Question 36

What does internal energy change equal during isothermal expansion?

Answer 36

delta u = q + w = 0 q = -w

Question 37

Ideal gas law

Answer 37

PV = nRT

Question 38

What is R and units?

Answer 38

8.314 j / mol k .08206 L atm / K mol

Question 39

For expansion is irreversible or reversible work larger magnitude?

Answer 39

rev > irrev

Question 40

What is internal energy?

Answer 40

Internal energy is the sum of all of the energies including chemical, kinetic, and potential

Question 41

Why does an ideal diatomic gas have a higher heat capacity than an ideal monatomic gas?

Answer 41

A diatomic gas has more degrees of freedom because it also occupies rotational and sometimes vibrational states at room temperature. Monatomic gases only occupy 3 translational modes +2 rotational modes at room temperature

Question 42

Describe the internal energy of an ideal gas

Answer 42

only depends on temperature, not pressure or volume