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Thermal Physics Flashcards

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1
Q

What’s Avogadro’s number

A

6.02x10^23

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2
Q

Define molar mass

A

Mass of one mole of a substance

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3
Q

Define molecule mass

A

Mass of one molecule in a substance

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4
Q

How to work out kelvin

A

Subtract 273 from the temperature in Celsius

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5
Q

What’s is Boyle’s law

A

Pressure of gas’s in inversely proportional to volume
P1/p2 = v2/v1

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6
Q

What’s Charles’ law

A

Volume of gas id directly proportional to temperature
When pressure is constant
V1/T1 = V2/T2

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7
Q

What’s the pressure law

A

Pressure of gas is directly proportional to temperature
P1/T1 = P2/T2

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8
Q

What’s the equation that summarises the tree gas laws

A

pV/T =constant
V1p1/T1 = V2p2/T2

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9
Q

What’s the molar gas constant

A

8.31 jk-1 mol-1

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10
Q

What’s the Boltzmann equation

A

An alternative for the ideal gas equation
Vp= NkT

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11
Q

What’s is Boltzmann constant

A

K= 1.38 x10^-23

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12
Q

Define pressure

A

Force per unit surface area which the force acts on
P= F/A

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13
Q

What are the five ideal gas law assumptions

A
  1. The volume of gas is negligible compared to the volume of occupied gas
  2. The force attraction between the molecule are negligible. The molecules only influence each o their during collisions
  3. The time between collisions with the containers wall and the other molecules are much greater than the duration of a collision
  4. The collision between molecules within the wall of the container contain elastic
  5. There are a large number of molecules whose motion is random
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14
Q

Explain Boyle’s law

A
  1. Has a fixed temperature so momentum change, of each molecule is the same
  2. More collisions per second so total momentum change is bigger
  3. So larger force exerted on container wall
  4. So large pressure exerted
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15
Q

Explain Charles law

A
  1. Average kinetic energy of molecule increases
  2. So change in momentum of each collision is greater
  3. To keep the total force and pressure constant the volume increases
  4. Increasing the time between collisions
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16
Q

Explain pressure law

A
  1. Average kinetic energy of molecule increases
  2. So change in momentum of each collision in greater
  3. Volume is constant so the talas force increases
  4. Increasing pressure exerted
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17
Q

What are the main two ways in which energy can transfer from one place to another?

A
  1. When work is done on an object
  2. If one object is hotter than another and conduction, convection or radiation occur
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18
Q

What are the two types of energy that molecules in a hot substance will have?

A

Kinetic and potential

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19
Q

What is internal energy?

A

The sum of the randomly distributed kinetic and potential energies of the particles in a body

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20
Q

What is the symbol for internal energy?

A

U

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21
Q

What is internal energy measured in?

A

J

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22
Q

What is the first law of thermodynamics?

A

The change of internal energy of the object is equal to the total energy transfer due to work done and heating

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23
Q

What is the first law of thermodynamics linked to?

A

Conservation of energy

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24
Q

What is a useful outcome of the first law of thermodynamics?

A

If work is being done on an object and it is not increasing its internal energy, then it must have an output rate identical to the work being done on it

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25
Q

What happens when a sample is heated?

A

heat energy supplied increases internal energy

  • Ek increases, so mean molecular speed increases
  • also mean separation slightly increased so small increase in molecular Ep
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26
Q

What happens when a samples changes state?

A

temperature remains constant

  • so mean Ek is constant
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27
Q

When a sample is changing state, what is the energy being used for?

A

To break bonds as the sample melts or boils

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28
Q

What does heat flow result from?

A

Temperature difference

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29
Q

What happens if two objects at different temperatures are placed in thermal contact?

A

Heat flows from the higher to the lower temperature until the temperatures equalise

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30
Q

When will two bodies be in thermal equilibrium?

A

When two objects at different temperatures are placed in thermal contact and heat flows from the higher to the lower temperature until the temperatures equalise

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31
Q

What happens to internal energy when a substance is hotter?

A

It is increased

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32
Q

What does a temperature scale require?

A

Two fixed points with fixed degrees between them

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33
Q

What is steam point?

A

The temperature of pure steam at standard atmospheric pressure

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34
Q

What is the lowest possible temperature on the absolute scale?

A

0K

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35
Q

What is definition of the triple point of water?

A

The temperature at which water can exist in all three states

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36
Q

How do you convert from Kelvin to Celsius?

A

Add 273.15

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37
Q

What happens when you cool a gas within a fixed volume?

A

Its pressure drops

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38
Q

If you plot a graph of pressure against temperature, with different gases, where will the lines intercept?

A

At absolute 0, on the negative x-axis

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39
Q

What unit does the absolute scale use?

A

Kelvin

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40
Q

What does the rise in temperature for a substance being heated depend on?

A
  • mass of substance
  • how much energy is put in
  • what the substance is
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41
Q

What is the equation for the energy required to heat a substance?

A

E = mcΔθ

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42
Q

What is m in E = mcΔθ?

A

Mass (kg)

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43
Q

What is c in E = mcΔθ?

A

Specific heat capacity (Jkg⁻¹K⁻¹)

44
Q

What is Δθ in E = mcΔθ?

A

Temperature change (°C or K)

45
Q

What is the specific heat capacity of a substance?

A

The energy needed to raise the temperature of unit mass of the substance by 1K without change of state

46
Q

What is the symbol for specific heat capacity?

A

c

47
Q

How can adding an exact amount of energy to a system be achieved?

A

By doing work on the system

48
Q

What experiment can be carried out to find the specific heat capacity of a metal?

A

block of metal of known mass in insulated container

  • heater and thermometer inserted
  • temperature rise measured
  • energy supplied = heat current x pd x time
  • c = IVt / mΔT
49
Q

To find the specific heat capacity of a liquid instead of a metal, what changes must be made?

A

Liquid placed inside container instead and stirred

50
Q

What equipment is used to find the specific heat capacity of a liquid?

A

Calorimeter

51
Q

What must be included in the calculations to find the specific heat capacity of a liquid? Why is this?

A

The specific heat capacity of the calorimeter, as it absorbs energy

52
Q

What does the rate of change of temperature in boilers and showers create?v

A

A rate of energy input, which is power

53
Q

What is the equation that is useful in continuous flow heating?

A

IV = P = mcΔT / t

54
Q

What are the units of c?

A

J kg⁻¹ K⁻¹

55
Q

What does the rate of energy flow to sustain the heating in a system calculate?

A

The power in Watts

56
Q

Properties of solids?

A

maintain shape

  • constant volume
  • cannot be easily compressed
  • molecules/atoms close together and vibrate in fixed positions
57
Q

Properties of liquids?

A
  • flow and take shape of vessel
  • constant volume
  • cannot be easily compressed
  • molecules/atoms are close together and can move around each other
58
Q

Properties of gases?

A
  • flow and take any shape, fill any space
  • take the volume of any vessel or space
  • can be easily compressed
  • molecules/atoms are far apart and are free to move
59
Q

What will be proportional to the energy supplied when a pure substance is heated?

A

temp

60
Q

Does a material change state at a constant temperature?

A

yes

61
Q

Why is the energy transferred to a substance to melt/boil it not obvious or ‘hidden’?

A

Temperature does not change during the change of state

62
Q

What is the energy needed to make a change of state occur?

A

Latent heat

63
Q

What is latent heat?

A

The energy needed to make a change of state occur

64
Q

What is the latent heat of fusion?

A

The energy needed to melt a substance

65
Q

What is the latent heat of vaporisation?

A

The energy needed to evaporate a substance

66
Q

What is specific latent heat?

A

How much energy is needed to make a unit mass of a pure substance change state

67
Q

Q
What are the units for specific latent heat?

A

J kg⁻¹

68
Q

On a temperature-time graph, what does the gradient represent?

A

The rate of change of temperature

69
Q

On a temperature-time graph, what will a steeper gradient show?

A

That state heats more quickly - and has a lower specific heat capacity

70
Q

On a temperature-time graph, what is the length of time to change state proportional to?

A

The specific latent heat for each state change

71
Q

What is the equation for specific latent heat?

A

E = ml

72
Q

What does E stand for in E = ml?

A

Energy (J)

73
Q

Q
What does l stand for in E = ml?

A

Specific latent heat (Jkg⁻¹)

74
Q

Q
What is the pressure of a gas?

A

The force per unit area that is exerts at right angles to surface

75
Q

What is pressure affected by?

A

temperature

  • volume
  • mass of gas particles
76
Q

What are the units of pressure?

A

pascals (Pa or Nm⁻²)

77
Q

Q
What type of collisions do gas molecules have with the walls of the container?

A

Elastic

78
Q

Why do gas molecules move at the same speed after they have collided with the container wall?

A

The collisions are elastic

79
Q

What is the magnitude of pressure proportional to?

A

The rate of collisions with the container wall

80
Q

How can the pressure of a gas be increased?

A

increasing temperature - particles move faster

  • reducing volume of container - increases chance of particles colliding with wall
  • adding more gas - increasing the number of particles
81
Q

What is Boyle’s law in words?

A

The pressure of a fixed mass of gas at constant temperature is inversely proportional to its volume

boils have volume and are hot (volume + temp)

82
Q

What is Boyle’s law in equations?

A

p ∝ 1/V

pV = constant

83
Q

What is an isothermal change?

A

An experiment done at constant temperature

84
Q

Q
For a Boyle’s law experiment at constant temperature, what shape will a pressure-volume graph be?

A

Downwards curve

85
Q

How could a pressure-volume graph for a Boyle’s law experiment be made into a straight line?

A

Plot p against 1/V

86
Q

What is Charles’ law?

A

Reducing the temperature of a gas but maintaining the same pressure causes the volume to decrease

87
Q

In Charles’ law, what does volume increase in proportion to?

A

Absolute temperature

88
Q

What is the equation for Charles’ law?

A

V = constant T

89
Q

In a Charles’ law experiment, what condition must there be for the x-intercept to be at absolute zero?

A

The gas must be ideal

90
Q

What must happen if a volume of gas is compressed but the pressure is maintained?

A

Heat must be transferred

91
Q

What happens when you reduce the temperature of a gas at a fixed volume?

A

Pressure is reduced

92
Q

What equation relates to the pressure law?

A

p = constant times T

93
Q

What are the three relationships between volume, pressure and temperature?

A
  • Boyle’s law
  • Charles’ law
  • The pressure law
94
Q

What is an ideal gas?

A

One which obeys the gas law exactly

95
Q

When can real gas behaviour be classed as ideal?

A

When gases are considered at low pressures and higher temperatures

96
Q

What can the gas laws be combined to give?

A

PV/T = constant

or

P₁V₁ / T₁ = P₂V₂ / T₂

97
Q

Q
What must be true of a gas to be ideal?

A
  • particles themselves can be thought of as taking up no volume
  • no significant forces between particles
  • motion of particles is random
98
Q

Q
What is Brownian motion?

A

The random movement of particles in a fluid

99
Q

What is responsible for diffusion?

A

Brownian motion

100
Q

Why must the same volume of two gases at the same temperature contain the same number of particles?

A

Because the particles in an ideal gas take up no volume themselves

101
Q

What is the word definition of the Avogadro constant?

A

The number of carbon atoms in 12g of carbon-12

102
Q

Why did the definition of Avogadro’s constant change from using hydrogen to carbon?

A

It is difficult to get a pure enough sample of Hydrogen-1 without isotopes being present

103
Q

What is the value of the Avogadro constant?

A

6.023 x 10²³

104
Q

How many
particles does one mole of a pure substance contain?

A

Avogadro’s number

105
Q

What is the molarity of a sample?

A

How many moles in contains - unit is mol

106
Q

What is the molar mass of a sample?

A

The mass of 1 mol in kgmol⁻¹

107
Q

Equation for number of molecules in a specific mass?

A

Ms = NA x Ms / Molar mass

Physics (3 decks)

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