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A-Level PHYSICS Edexcel > Topic 9- Thermodynamics > Flashcards

Topic 9- Thermodynamics Flashcards

1
Q

specific heat capacity

A

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

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2
Q

specific heat capacity equation

A

Δe = mcΔθ

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3
Q

measuing specific heat capacity experiment

A
  1. insulate the material and place and heater and thermometer inside it (solid or liquid)
  2. heat the substance for a set amount of time
  3. measure the change in temperature of the substance.
  4. using the power of the heating appliance use E = Pt to calculate the energy
  5. use Δe = mcΔθ to calculate the value value of c
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4
Q

units of specfic 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 a subtance melts or boil (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 vapourisation

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
  1. place a beaker of cold water on a top pan balance with a heater in it
  2. heat the water for a set time
  3. measure the change in mass during the heating
  4. work out the energy inputted from the power of the heating appliance E=pt
  5. 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 equilibirum

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19
Q

thermal equilibirum

A

two systems are at the same temperature so there is no resultant flow of heat between themWhat

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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

Boyles 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 the Pressure, P, doubles to 2P the volume, V, ….

A

halves to 1/2V

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33
Q

Boyles law experiment

A
  1. slowly use the foot pump to increase the pressure
  2. record the volume for different pressure level
  3. plot p agaisnt 1/v, if the graph is directly proportional it follows boyles law
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34
Q

Charles 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 law experiment

A
  • record the volume and temperature of the cold water
  • heat the water and record the temperatures
  • plot volume agaisnt temperature. If the graph is straight line and approximately crosses the x-axis at -273 degrees it follows Charles law
39
Q

Gay Lussacs pressure law

A

far 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 Lussacs experiment

A
  1. heat is applied to the cylinder
  2. measure the temperature and volume at regular intervals
  3. plot P agaisnt T if its a straight line graph then it obeys the law
43
Q

How does gay lussacs and charles experiments give evidence for an absolute zero temperature

A

They should be directly proportional however they are not and both intersect the x axis at -273. 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 no obey the gas laws as well

A
  • if too cold they condense
  • if under too much pressure they condense
  • molecule interactions result in imperfect result
46
Q

How did they find the exact value of absolute zero

A

extrapolating the graph from charles law and gaylussacs 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

boltzman constant

51
Q

pressure in a container of gas

A

particles move about and collide with the walls of the the container the change in momentum causes a force on the side of the container which results 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
  1. when the loecules bounce off the side of the box its momentum changes from +mv to -mv so change in momentum is -2mv
  2. the time for the molecule to get back to its original position is 2L/v (v=st)
  3. the force on the side of the cube is calculated by: F = Δp/Δt = 2mv/ (2L/v) = mv^2/L
  4. P = F/A where A = L^2 so P= mv^2/V
  5. if the box contained N molecules the pressure would increase by N times so P = Nmv^2/V
  6. since the molecules move in all directions we can assume there is a third of each direction so P = Nmv^2/3V
  7. all the molecular speed vary so we used 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

Whats 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
  1. square all the values
  2. take the mean
  3. 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 behaviour 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

wiens law

A

λmax T = 0.0029

66
Q

What does wiens 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 intensity against wavelength graph change?

A

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

70
Q

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

A

exponential decay, its not due to the ultraviolet catastrophe

71
Q

What causes line spectra

A

After an electron has been exicted 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 m^2 (intensity)

x axis - wavelength

77
Q

area under a boltzmann distrubution

A

number of particles

78
Q

boltzmann distrubution axes

A

y axis - number of molecules

x axis - kinetic energy / speed

79
Q

the greater the photon energy (hf)…

A

the greater then number of energy levels the electron moves up

80
Q

internal energy of a gas

A

Just kinetic energy (no PE)

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
  • therefore 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.

A-Level PHYSICS Edexcel (16 decks)

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