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AQA A Level Physics > 6.2 Thermal Physics > Flashcards

6.2 Thermal Physics Flashcards

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1
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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2
Q

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

A

Kinetic and potential

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3
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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4
Q

What is the symbol for internal energy?

A

U

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5
Q

What is internal energy measured in?

A

J

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6
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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7
Q

What is the first law of thermodynamics linked to?

A

Conservation of energy

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8
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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9
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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10
Q

What happens when a samples changes state?

A
  • temperature remains constant

* so mean Ek is constant

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11
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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12
Q

What does heat flow result from?

A

Temperature difference

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13
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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14
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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15
Q

What happens to internal energy when a substance is hotter?

A

It is increased

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16
Q

What does a temperature scale require?

A

Two fixed points with fixed degrees between them

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17
Q

What is 0°C in the Celsius scale?

A

Ice point

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18
Q

What is 100°C in the Celsius scale?

A

Steam point

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19
Q

What is steam point?

A

The temperature of pure steam at standard atmospheric pressure

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20
Q

What is the lowest possible temperature on the absolute scale?

A

0K

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21
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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22
Q

What is the value of the triple point of water?

A

273.16 K

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23
Q

What is the value of the ice point of water in K?

A

273.15 K

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24
Q

How do you convert from Kelvin to Celsius?

A

Add 273.15

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25
Q

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

A

Its pressure drops

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26
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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27
Q

What unit does the absolute scale use?

A

Kelvin

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28
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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29
Q

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

A

E = mcΔθ

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30
Q

What is m in E = mcΔθ?

A

Mass (kg)

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31
Q

What is c in E = mcΔθ?

A

Specific heat capacity (Jkg⁻¹K⁻¹)

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32
Q

What is Δθ in E = mcΔθ?

A

Temperature change (°C or K)

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33
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

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34
Q

What is the symbol for specific heat capacity?

A

c

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35
Q

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

A

By doing work on the system

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36
Q

In the inversion tube experiment, what happens in terms of energy transfers?

A

As the contents fall down tube, potential energy is converted into thermal energy

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37
Q

If the inversion tube experiment is repeated n times, what is the equation for total energy change?

A

E = mgLn

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38
Q

What is measured in the inversion tube experiment?

A

The temperature change of the balls inside the tube

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39
Q

What equation can help to calculate specific heat capacity in the inversion tube experiment?

A

c = gLn / ΔT

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40
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
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41
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

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42
Q

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

A

Calorimeter

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43
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

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44
Q

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

A

A rate of energy input, which is power

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45
Q

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

A

IV = P = mcΔT / t

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46
Q

What are the units of c?

A

J kg⁻¹ K⁻¹

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47
Q

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

A

The power in Watts

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48
Q

Properties of solids?

A
  • maintain shape
  • constant volume
  • cannot be easily compressed
  • molecules/atoms close together and vibrate in fixed positions
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49
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
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50
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
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51
Q

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

A

Its temperature

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52
Q

Does a material change state at a constant temperature?

A

Yes

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53
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

54
Q

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

A

Latent heat

55
Q

What is latent heat?

A

The energy needed to make a change of state occur

56
Q

What is the latent heat of fusion?

A

The energy needed to melt a substance

57
Q

What is the latent heat of vaporisation?

A

The energy needed to evaporate a substance

58
Q

What is specific latent heat?

A

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

59
Q

What are the units for specific latent heat?

A

J kg⁻¹

60
Q

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

A

The rate of change of temperature

61
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

62
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

63
Q

What is the equation for specific latent heat?

A

E = ml

64
Q

What does E stand for in E = ml?

A

Energy (J)

65
Q

What does m stand for in E = ml?

A

Mass (kg)

66
Q

What does l stand for in E = ml?

A

Specific latent heat (Jkg⁻¹)

67
Q

What is the specific latent heat of fusion of ice?

A

3.3. x 10³ Jkg⁻¹

68
Q

What is the specific latent heat of vaporisation of water?

A

22.6 x 10³ Jkg⁻¹

69
Q

What is the pressure of a gas?

A

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

70
Q

What is pressure affected by?

A
  • temperature
  • volume
  • mass of gas particles
71
Q

What are the units of pressure?

A

pascals (Pa or Nm⁻²)

72
Q

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

A

Elastic

73
Q

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

A

The collisions are elastic

74
Q

What is the magnitude of pressure proportional to?

A

The rate of collisions with the container wall

75
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
76
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

77
Q

What is Boyle’s law in equations?

A

p ∝ 1/V

pV = constant

78
Q

What is an isothermal change?

A

An experiment done at constant temperature

79
Q

What is an experiment done at constant temperature?

A

Isothermal change

80
Q

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

A

Downwards curve

81
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

82
Q

What is Charles’ law?

A

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

83
Q

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

A

Absolute temperature

84
Q

In a graph showing Charles’ law, where will the x-intercept always occur?

A

At -273.15 °C (absolute zero)

85
Q

What is the equation for Charles’ law?

A

V/T = constant

86
Q

What is an experiment done at constant pressure?

A

An isobaric change

87
Q

What is an isobaric change?

A

An experiment done at constant pressure

88
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

89
Q

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

A

Heat must be transferred

90
Q

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

A

Pressure is reduced

91
Q

What equation relates to the pressure law?

A

p / T = constant

92
Q

What has the same shape as a Charles’ law (volume-temperature) graph?

A

Pressure against temperature

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

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

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 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 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

108
Q

How is the constant calculated in pV/T = constant?

A
  • plot pV against T (in K)
  • straight line through origin - find gradient (nR)
  • rearrange formula: pV = nRT
109
Q

What is the Boltzmann constant?

A

A way of using the ideal gas equation to know the number of particles

110
Q

What equation is formed when the Boltzmann constant is used in pV/T = constant?

A

pV = NkT

111
Q

What does k equal in pV = NkT?

A

k = R/NA = 1.38 x 10⁻²³ JK⁻¹

112
Q

How to calculate the root mean square?

A

Square every value, divide by the number of data points then square root the total

113
Q

What does the graph of the speeds of molecules in a gas look like?

A

A bell curve

114
Q

What is a useful value to compare the speeds of molecules at different temperatures?

A

Root mean square of their speeds

115
Q

What are the 6 assumptions that have to be made to create a kinetic theory equation?

A
  • the particles themselves take up no volume
  • there is no force of attraction between the particles
  • their motion is random
  • their collisions are elastic
  • the length of time of the collisions against the walls of the container and each other are negligible
  • Newton’s laws of motion can be applied
116
Q

What are the three factors that affect the pressure of a gas in a given volume?

A
  • mass of molecules
  • speed of molecules
  • how many molecules there are in the container
117
Q

What is the theoretical equation for an ideal gas?

A

PV = 1/3 Nmc²

118
Q

What does P mean in PV = 1/3 Nmc²?

A

Pressure (Pa)

119
Q

What does V mean in PV = 1/3 Nmc²?

A

Volume (m³)

120
Q

What does N mean in PV = 1/3 Nmc²?

A

Number of molecules

121
Q

What does m mean in PV = 1/3 Nmc²?

A

Mass of one molecule (kg)

122
Q

What does c mean in PV = 1/3 Nmc²?

A

Average molecular speed (ms⁻¹)

123
Q

What happens when you combine the theoretical equation for ideal gas and the ideal gas equation?

A

1/2mc² = 3RT/2Na = 3/2 kt

124
Q

How is E = 3/2mc² formed from 1/2mc² = 3RT/2Na = 3/2 kt?

A

Because 1/2 mc² is the mean kinetic energy of a gas molecule

125
Q

What is the temperature of a gas a mean of?

A

The average kinetic energy of the particles

126
Q

How can you calculate the mean kinetic energy of the molecules?

A

By dividing total energy by the number of particles

127
Q

Equation to calculate mean kinetic energy of molecules?

A

E = 1/2 m(c RMS)²

128
Q

What are the two useful formulas to find the mean kinetic energy of molecules?

A
  • E = 1/2 m(c RMS)²

* E = 3/2kT

129
Q

How can the total energy of n moles of a gas at temperature T kelvin be calculated?

A

3/2 nRT

130
Q

How can internal energy be calculated?

A

3/2 nRT

131
Q

Make sure you practice how to derive the kinetic energy equation.

A

Ok.

AQA A Level Physics (10 decks)

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