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Physics paper 2 > Thermal physics > Flashcards

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

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
In the inversion tube experiment, what happens in terms of energy transfers?
As the contents fall down tube, potential energy is converted into thermal energy
26
If the inversion tube experiment is repeated n times, what is the equation for total energy change?
E = mgLn (Not given on formula sheet)
27
What equation can help to calculate specific heat capacity in the inversion tube experiment?
c = gLn / ΔT
28
What equipment is used to find the specific heat capacity of a liquid?
Calorimeter
29
What must be included in the calculations to find the specific heat capacity of a liquid? Why is this?
The specific heat capacity of the calorimeter, as it absorbs energy
30
What will be proportional to the energy supplied when a pure substance is heated?
Its temperature
31
What is the energy needed to make a change of state occur?
Latent heat
32
What is latent heat?
The energy needed to make a change of state occur
33
What is the latent heat of fusion?
The energy required to change the state of 1kg/unit mass of a solid to a liquid without changing its temperature
34
What is the latent heat of vaporisation?
The energy required to change the state of 1kg/unit mass of a liquid to a gas without changing its temperature
35
What is specific latent heat?
How much energy is needed to make a 1kg/unit mass of a pure substance change state
36
What are the units for specific latent heat?
J kg⁻¹
37
On a temperature-time graph, what does the gradient represent?
The rate of change of temperature
38
On a temperature-time graph, what will a steeper gradient show?
That state heats more quickly - and has a lower specific heat capacity
39
On a temperature-time graph, what is the length of time to change state proportional to?
The specific latent heat for each state change
40
What is the equation for specific latent heat? (energy to change state)
Q = ml Q = Energy (J) m = Mass (Kg) l = Specific latent heat (Jkg⁻¹)
41
What is the specific latent heat of fusion of ice?
3.3. x 10³ Jkg⁻¹
42
What is the specific latent heat of vaporisation of water?
22.6 x 10³ Jkg⁻¹
43
What is the pressure of a gas?
The force per unit area that is exerts at right angles to surface
44
What is pressure affected by?
-Temperature -Volume -Mass of gas particles
45
What are the units of pressure?
Pascals (Pa or Nm⁻²)
46
What type of collisions do gas molecules have with the walls of the container?
Elastic
47
What is the magnitude of pressure proportional to?
The rate of collisions with the container wall
48
How can the pressure of a gas be increased?
-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
What is Boyle’s law in words?
The pressure of a fixed mass of gas at constant temperature is inversely proportional to its volume
50
What is Boyle’s law in equations?
p ∝ 1/V pV = constant (Not given on formula sheet)
51
What is an isothermal change?
An experiment done at constant temperature
52
What is an isobaric change?
An experiment done at constant pressure
53
What is an isochoric change?
An experiment done at constant volume
54
What is an adiabatic change?
An experiment where no heat is transfered in or out of the system
55
What is Charles’ law?
Reducing the temperature of a gas but maintaining the same pressure causes the volume to decrease
56
In Charles’ law, what does volume increase in proportion to?
Absolute temperature
57
In a graph showing Charles’ law, where will the x-intercept always occur?
At -273.15 °C (absolute zero)
58
What is the equation for Charles’ law?
V = constant T (Not given on formula sheet)
59
In a Charles’ law experiment, what condition must there be for the x-intercept to be at absolute zero?
The gas must be ideal
60
What must happen if a volume of gas is compressed but the pressure is maintained?
Heat must be transferred
61
What happens when you reduce the temperature of a gas at a fixed volume?
Pressure is reduced
62
What equation relates to the pressure law?
p = constant times T
63
What are the three relationships between volume, pressure and temperature?
-Boyle’s law -Charles’ law -The pressure law
64
What is an ideal gas?
One which obeys the gas law exactly
65
When can real gas behaviour be classed as ideal?
When gases are considered at low pressures and higher temperatures
66
What can the gas laws be combined to give?
PV/T = constant or P₁V₁ / T₁ = P₂V₂ / T₂ (Not given on equation sheet)
67
What must be true of a gas to be ideal?
-Particles themselves can be thought of as taking up no volume -No significant forces between particles -Motion of particles is random
68
What is Brownian motion?
The random movement of particles in a fluid
69
What is responsible for diffusion?
Brownian motion
70
What is the word definition of the Avogadro constant?
The number of carbon atoms in 12g of carbon-12
71
Why did the definition of Avogadro’s constant change from using hydrogen to carbon?
It is difficult to get a pure enough sample of Hydrogen-1 without isotopes being present
72
What is the value of the Avogadro constant?
6.023 x 10²³
73
How many particles does one mole of a pure substance contain?
Avogadro’s number
74
What is the molarity of a sample?
How many moles in contains - unit is mol
75
The mole formula
m = n x Mr m = mass (Kg) n = moles (mol) Mr = molar mass (g/mol) (Not given on formula sheet)
76
How is the constant calculated in pV/T = constant?
-Plot pV against T (in K) -Straight line through origin - find gradient (nR) -Rearrange formula: pV = nRT
77
What is the Boltzmann constant?
A way of using the ideal gas equation to know the number of particles
78
What equation is formed when the Boltzmann constant is used in pV/T = constant?
pV = NkT
79
What does k equal in pV = NkT?
k= Boltzmann constant = R/NA = 1.38 x 10⁻²³ JK⁻¹
80
How to calculate the root mean square?
Square every value, divide by the number of data points then square root the total
81
What is a useful value to compare the speeds of molecules at different temperatures?
Root mean square of their speeds
82
Define what is meant by an ideal gas?
-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
What are the three factors that affect the pressure of a gas in a given volume?
-Mass of molecules -Speed of molecules -How many molecules there are in the container
84
What is the theoretical equation for an ideal gas?
PV = 1/3 Nmc²
85
What is the temperature of a gas a mean of?
The average kinetic energy of the particles
86
How can you calculate the mean kinetic energy of the molecules?
By dividing total energy by the number of particles

Physics paper 2 (7 decks)

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