Quiz 1 Flashcards

1
Q

What is the first law of thermodynamics?

A

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

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2
Q

What is an open system?

A

heat and matter exchange with the surroundings

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3
Q

What is a closed system?

A

only heat exchanges with the surroundings

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4
Q

What is an isolated system?

A

no heat or matter exchange with the surroundings

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5
Q

What are heat and work (general)

A
  • different means energy is transferred in and out of a system
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6
Q

How does heat transfer energy?

A

due to temperature changes between system and surroundings

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7
Q

How does work transfer energy?

A

due to unbalanced forces between system and surroundings

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8
Q

How is the change in internal energy defined?

A

sum of heat transferred and work done is internal energy

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9
Q

What is a state function?

A
  • depends only on the difference between initial and final STATES, not the path
  • internal energy, enthalpy
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10
Q

What is a path function?

A
  • 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
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11
Q

What is an intensive quantity?

A
  • doesnt depend on the amount of substance present
  • temperature
  • pressure
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12
Q

What is an extensive quantity?

A
  • depends on the amount of the substance present
  • mass, internal energy
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13
Q

What molecular level properties determine C?

A
  • 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)
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14
Q

Heat capacity units

A

(J/K) extensive quantity

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15
Q

Molar heat capacity

A

(J/K mol) intensive quantity

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16
Q

Specific heat capacity

A

(J/ K g) heat capacity per mass

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17
Q

What is the equipartition theorem?

A
  • every quadratic term to the energy is equal to 1/2RT
18
Q

Apply Equipartition theorem to the oscillator.

A

Etotal = E kin + E pot
Etotal = RT

19
Q

Heat capacity of Monatomic Ideal gases

A

Cvm = 3/2 R

20
Q

Heat capacity of diatomic ideal gases

A
  • Equipartition theorem predicts
    C = 7/2 R
  • However the vibrational mode is not significantly populated at room temperature so C = 5/2 R
21
Q

What does large heat capacity indicate?

A

A lot of heat is required to change the temperature

22
Q

What is the heat capacity equation?

A

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

23
Q

Heat capacity of simple solids

A

C = 3R

24
Q

Why does the equipartition theorem only work at high temperature?

A
  • 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
25
Q

How does heat capacity change with temperature?

A
  • 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
26
Q

What factors affect the heat capacity of complex solids?

A
  • 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
27
Q

Why is Cp larger than Cv?

A

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

28
Q

What is the relationship between Cp and Cv ideal gas?

A

Cp = Cv + nR

29
Q

What is the enthalpy equation?

A

H = U + PV

30
Q

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

A
  • no additional work other than pV work (no electrical work)
  • the process must be carried out reversibly
31
Q

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

A
  • sudden removal of weight
    w = - pex (vf- vi)
32
Q

What is the reversible isothermal expansion of an ideal gas?

A
  • we remove infinitiesimally small amounts of sand in a stepwise manner so that pex = pgas
    wr = -nRT ln(V2/V1)
33
Q

Derive enthalpy equation

A

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

34
Q

Positive work

A

surroundings are doing work on the system

35
Q

Negative work

A

system doing work on the surroundings

36
Q

What does internal energy change equal during isothermal expansion?

A

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

37
Q

Ideal gas law

A

PV = nRT

38
Q

What is R and units?

A

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

39
Q

For expansion is irreversible or reversible work larger magnitude?

A

rev > irrev

40
Q

What is internal energy?

A

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

41
Q

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

A

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

42
Q

Describe the internal energy of an ideal gas

A

only depends on temperature, not pressure or volume