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Physics The Good One > 09 Thermodynamics > Flashcards

09 Thermodynamics Flashcards

1
Q

Specific Heat Capacity

A

The amount of energy needed to raise the temperature of 1kg of the substance by 1K

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2
Q

Specific Heat Capacity Equation

A

Δe = mcΔθ

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3
Q

Measuring Specific Heat Capacity Experiment

A

Insulate the material and place a heater and thermometer inside it (solid or liquid). Heat the substance for a set amount of time. Measure the change in temperature of the substance. Using the power of the heating appliance, use E = Pt to calculate the energy. Use Δe = mcΔθ to calculate the value of c.

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4
Q

Units of Specific Heat Capacity

A

J/kg/K

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5
Q

Why is the calculated value of c always too large?

A

Energy from the heater did not all go to increase the internal energy. Some will have escaped to increase the internal energy of the room.

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6
Q

Specific Latent Heat

A

The energy needed to change the state of 1kg of the substance without changing the temperature

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7
Q

What is Specific Latent Heat?

A

The energy needed to break the bonds as a substance melts or boils (changes state)

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8
Q

Latent Heat of Fusion

A

Solid -> Liquid (melting)

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9
Q

Latent Heat of Vaporization

A

Liquid -> Gas (boiling)

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10
Q

Latent Heat Equation

A

E = LΔm

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11
Q

Latent Heat Unit

A

J/kg

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12
Q

Measuring Latent Heat

A

Place a beaker of cold water on a top pan balance with a heater in it. Heat the water for a set time. Measure the change in mass during the heating. Work out the energy inputted from the power of the heating appliance (E = Pt). Work out the latent heat using E = LΔm.

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13
Q

Why doesn’t the temperature change when a substance is changing state?

A

The energy is being used to change the state.

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14
Q

Internal Energy

A

The sum of the kinetic and potential energy within a system.

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15
Q

Heating

A

The process when energy is transferred from a higher-temperature object to a lower-temperature object.

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16
Q

Heat

A

The energy transferred by heating.

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17
Q

1st Law of Thermodynamics

A

Energy in a system is conserved: change in internal energy = heat transfer + work done (U = Q + W).

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18
Q

0th Law of Thermodynamics

A

If two systems are at the same temperature, there is no resultant flow of heat between them; the system is in thermal equilibrium.

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19
Q

Thermal Equilibrium

A

Two systems are at the same temperature, so there is no resultant flow of heat between them.

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20
Q

What can happen when the internal energy increases?

A

Increase in temperature; change state.

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21
Q

What does doubling the number of atoms do?

A

Doubles the time to heat up.

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22
Q

As the temperature of a gas increases:

A

Average particle speed increases. The maximum particle speed increases. The distribution curve becomes more spread out.

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23
Q

How is energy transferred between particles?

A

Via momentum in collisions.

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24
Q

Kelvin -> Celsius

A

θ = T - 273

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25
Q

Celsius -> Kelvin

A

T = θ + 273

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26
Q

Boyle’s Law

A

For a fixed mass of gas at constant temperature, pressure (p) is inversely proportional to volume (V).

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27
Q

Work Done (W) =

A

Pressure (p) × Change in Volume (V)

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28
Q

Pressure-Volume Graph

A

1/x curve

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29
Q

Pressure (1/V) Graph

A

Straight-line graph through the origin

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30
Q

PV =

A

A constant

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31
Q

P1V1 =

A

P2V2

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32
Q

As Pressure (P) doubles to 2P, the Volume (V)…

A

Halves to 1/2V

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33
Q

Boyle’s Law Experiment

A

Slowly use the foot pump to increase the pressure. Record the volume for different pressure levels. Plot p against 1/v. If the graph is directly proportional, it follows Boyle’s Law.

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34
Q

Charles’s Law

A

For a fixed mass of gas at constant pressure, the volume (V) is (directly) proportional to the temperature (T) in kelvin.

35
Q

V/T =

A

A constant

36
Q

V1/T1 =

A

V2/T2

37
Q

Volume-Temperature Graph

A

Straight line. If in kelvin, directly proportional. If in Celsius, cuts the y-axis.

38
Q

Charles’s Law Experiment

A

Record the volume and temperature of the cold water. Heat the water and record the temperatures. Plot volume against temperature. If the graph is a straight line and approximately crosses the x-axis at -273°C, it follows Charles’s Law.

39
Q

Gay-Lussac’s Pressure Law

A

For a fixed mass of gas at constant volume, pressure is proportional to temperature.

40
Q

P/T =

A

A constant

41
Q

P1/T1 =

A

P2/T2

42
Q

Gay-Lussac’s Experiment

A

Heat is applied to the cylinder. Measure the temperature and volume at regular intervals. Plot P against T. If it’s a straight-line graph, it obeys the law.

43
Q

How do Gay-Lussac’s and Charles’s experiments give evidence for absolute zero temperature?

A

They should be directly proportional; however, they are not and both intersect the x-axis at -273°C. This gives evidence for the Kelvin temperature scale where 0K is absolute zero.

44
Q

Ideal Gas

A

A gas where the molecules do not interact.

45
Q

Why do real gases not obey the gas laws as well?

A

If too cold, they condense. If under too much pressure, they condense. Molecule interactions result in imperfect results.

46
Q

How did they find the exact value of absolute zero?

A

Extrapolating the graph from Charles’s Law and Gay-Lussac’s Law.

47
Q

Absolute Zero

A

The lowest possible temperature where all particles have the minimum possible kinetic energy.

48
Q

How are Kelvin and Celsius linked?

A

They have the same interval.

49
Q

Ideal Gas Equation

A

pV = NkT

50
Q

What is k in the Ideal Gas Equation?

A

Boltzmann constant

51
Q

Pressure in a container of gas

A

Particles move about and collide with the walls of the container. The change in momentum causes a force on the side of the container, resulting in pressure P = F/A.

52
Q

A gas is ideal if:

A

Molecules have negligible size. Molecules are identical. Collisions are perfectly elastic. No inter-molecular forces. Enough molecules for statistical analysis. Motion is random.

53
Q

Derive pV = 1/3Nm

A

When molecules bounce off the side of the box, their momentum changes from +mv to -mv so change in momentum is -2mv. The time for the molecule to get back to its original position is 2L/v (v=st). The force on the side of the cube is calculated by: F = Δp/Δt = 2mv/(2L/v) = mv^2/L. P = F/A where A = L^2 so P = mv^2/V. If the box contained N molecules, the pressure would increase by N times so P = Nmv^2/V. Since the molecules move in all directions, we assume there is a third of each direction so P = Nmv^2/3V. All the molecular speeds vary, so we use the root mean square P = Nm/3V.

54
Q

What does a Maxwell-Boltzmann distribution look like for lower temperatures?

A

Close together, higher peak.

55
Q

What does a Maxwell-Boltzmann distribution look like for higher temperatures?

A

Spread out, lower peak.

56
Q

What’s on the axes of a Maxwell-Boltzmann distribution?

A

Number of molecules against speed.

57
Q

What does the peak of a Maxwell-Boltzmann distribution show?

A

The most probable speed.

58
Q

How to calculate the root mean square?

A

Square all the values, take the mean, square root.

59
Q

What can 1/2m = 3/2RT be used for?

A

To calculate the mean kinetic energy.

60
Q

How to derive 1/2m = 3/2RT

A

Equate pV = NkT and pV = 1/3Nm.

61
Q

Black Body

A

A body that absorbs and emits all incident radiation of all wavelengths. It is a perfect emitter and a perfect radiator.

62
Q

Why is the predicted behavior of a black body not true?

A

Due to the ultraviolet catastrophe.

63
Q

Stefan-Boltzmann Law

A

L = σAT^4

64
Q

What does the Stefan-Boltzmann Law do?

A

Links the factors of a black body.

65
Q

Wien’s Law

A

λmax T = 0.0029

66
Q

What does Wien’s Law explain?

A

The relationship between peak wavelengths and the temperature of a body.

67
Q

In terms of molecular energy changes, why does the temperature remain constant when something boils?

A

The average kinetic energy is constant, and any input energy increases the potential energy, causing molecules to move further apart.

68
Q

What does an intensity against wavelength graph show?

A

The peak wavelength/distribution of wavelengths for a black body.

69
Q

If there is a higher temperature, how does the intensity against wavelength graph change?

A

The peak is higher and shifted to the left (the peaks do not align).

70
Q

Theoretically, what should an intensity against wavelength graph look like? Why doesn’t it look like this?

A

Exponential decay, it’s not due to the ultraviolet catastrophe.

71
Q

What causes line spectra?

A

After an electron has been excited, it drops back down the energy levels and releases energy in the form of photons, which are then detected and put into line spectra.

72
Q

What gives line spectra?

A

All elements.

73
Q

The hotter the object…

A

The more energy it emits.

74
Q

When drawing a blackbody curve:

A

The left-hand side must be drawn steeper than the right-hand side. The energy per second must decrease towards (but not reach) zero as the wavelength increases. The line must not cross the energy per second axis (y-axis).

75
Q

Higher temperature for Boltzmann vs Blackbody curves

A

Boltzmann - shifts right. Blackbody - shifts left.

76
Q

Axes for a blackbody curve graph

A

Y-axis - energy per second per m² (intensity), X-axis - wavelength.

77
Q

Area under a Boltzmann distribution

A

Number of particles.

78
Q

Boltzmann distribution axes

A

Y-axis - number of molecules, X-axis - kinetic energy/speed.

79
Q

The greater the photon energy (hf)…

A

The greater the number of energy levels the electron moves up.

80
Q

Internal Energy of a Gas

A

Just kinetic energy (no potential energy). KE = 3/2kT.

81
Q

Why does pressure decrease as it cools?

A

Reduced average kinetic energy, travels slower/less collisions with wall, change in momentum is less, therefore force on walls is less, and pressure is less.

82
Q

Condition to use PV/T = PV/T

A

One variable is constant, mass constant, acts as an ideal gas.

83
Q

Relationship between SHC and Number of Atoms

A

The energy required to raise the temperature of 1kg is proportional to the number of atoms in 1kg.

Physics The Good One (16 decks)

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