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Physics paper 2 > Thermal physics > Flashcards

Thermal physics Flashcards

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

Joules, 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 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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13
Q

What happens to internal energy when a substance is hotter?

A

It is increased

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14
Q

What is the lowest possible temperature on the absolute scale?

A

0K

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15
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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16
Q

What is the value of the triple point of water?

A

273.16 K

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17
Q

How do you convert from Kelvin to Celsius?

A

Add 273.15

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18
Q

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

A

Its pressure drops

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19
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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20
Q

What unit does the absolute scale use?

A

Kelvin

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21
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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22
Q

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

A

E = mcΔθ

Δθ = Temperature change (°C or K)
c = Specific heat capacity (Jkg⁻¹K⁻¹)
m = Mass (kg)

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23
Q

What is the specific heat capacity of a substance?

A

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

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24
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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25
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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26
Q

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

A

E = mgLn

(Not given on formula sheet)

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27
Q

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

A

c = gLn / ΔT

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28
Q

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

A

Calorimeter

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29
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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30
Q

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

A

Its temperature

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31
Q

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

A

Latent heat

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32
Q

What is latent heat?

A

The energy needed to make a change of state occur

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33
Q

What is the latent heat of fusion?

A

The energy required to change the state of 1kg/unit mass of a solid to a liquid without changing its temperature

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34
Q

What is the latent heat of vaporisation?

A

The energy required to change the state of 1kg/unit mass of a liquid to a gas without changing its temperature

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35
Q

What is specific latent heat?

A

How much energy is needed to make a 1kg/unit mass of a pure substance change state

36
Q

What are the units for specific latent heat?

A

J kg⁻¹

37
Q

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

A

The rate of change of temperature

38
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

39
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

40
Q

What is the equation for specific latent heat?
(energy to change state)

A

Q = ml

Q = Energy (J)
m = Mass (Kg)
l = Specific latent heat (Jkg⁻¹)

41
Q

What is the specific latent heat of fusion of ice?

A

3.3. x 10³ Jkg⁻¹

42
Q

What is the specific latent heat of vaporisation of water?

A

22.6 x 10³ Jkg⁻¹

43
Q

What is the pressure of a gas?

A

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

44
Q

What is pressure affected by?

A

-Temperature
-Volume
-Mass of gas particles

45
Q

What are the units of pressure?

A

Pascals (Pa or Nm⁻²)

46
Q

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

A

Elastic

47
Q

What is the magnitude of pressure proportional to?

A

The rate of collisions with the container wall

48
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

49
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

50
Q

What is Boyle’s law in equations?

A

p ∝ 1/V

pV = constant

(Not given on formula sheet)

51
Q

What is an isothermal change?

A

An experiment done at constant temperature

52
Q

What is an isobaric change?

A

An experiment done at constant pressure

53
Q

What is an isochoric change?

A

An experiment done at constant volume

54
Q

What is an adiabatic change?

A

An experiment where no heat is transfered in or out of the system

55
Q

What is Charles’ law?

A

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

56
Q

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

A

Absolute temperature

57
Q

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

A

At -273.15 °C (absolute zero)

58
Q

What is the equation for Charles’ law?

A

V = constant T

(Not given on formula sheet)

59
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

60
Q

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

A

Heat must be transferred

61
Q

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

A

Pressure is reduced

62
Q

What equation relates to the pressure law?

A

p = constant times T

63
Q

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

A

-Boyle’s law
-Charles’ law
-The pressure law

64
Q

What is an ideal gas?

A

One which obeys the gas law exactly

65
Q

When can real gas behaviour be classed as ideal?

A

When gases are considered at low pressures and higher temperatures

66
Q

What can the gas laws be combined to give?

A

PV/T = constant

or

P₁V₁ / T₁ = P₂V₂ / T₂

(Not given on equation sheet)

67
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

68
Q

What is Brownian motion?

A

The random movement of particles in a fluid

69
Q

What is responsible for diffusion?

A

Brownian motion

70
Q

What is the word definition of the Avogadro constant?

A

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

71
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

72
Q

What is the value of the Avogadro constant?

A

6.023 x 10²³

73
Q

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

A

Avogadro’s number

74
Q

What is the molarity of a sample?

A

How many moles in contains - unit is mol

75
Q

The mole formula

A

m = n x Mr

m = mass (Kg)
n = moles (mol)
Mr = molar mass (g/mol)

(Not given on formula sheet)

76
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

77
Q

What is the Boltzmann constant?

A

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

78
Q

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

A

pV = NkT

79
Q

What does k equal in pV = NkT?

A

k= Boltzmann constant = R/NA = 1.38 x 10⁻²³ JK⁻¹

80
Q

How to calculate the root mean square?

A

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

81
Q

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

A

Root mean square of their speeds

82
Q

Define what is meant by an ideal gas?

A

-Has molecules with negligible volume
-Collisions which are elastic
-Cannot be liquefied
-Has no interactions between the molecules (except during collisions)
-Obeys the ideal gas laws / Boyles law / Charles’ law / Pressure law
-At all temperature / pressures

83
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

84
Q

What is the theoretical equation for an ideal gas?

A

PV = 1/3 Nmc²

85
Q

What is the temperature of a gas a mean of?

A

The average kinetic energy of the particles

86
Q

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

A

By dividing total energy by the number of particles

Physics paper 2 (7 decks)

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