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A Level Physics Paper 2 > Thermal > Flashcards

Thermal Flashcards

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1
Q

What is one mole

A

The number of atoms in 12g of carbon 12

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2
Q

What is molar mass

A

M
The mass of one mole of substance
Roughly the nucleon number in grams per mole

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3
Q

Mass, moles, molar mass equation

A

Mass=Moles×Molar Mass

m=n×Mr

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4
Q

What is molecular mass

A

The mass of one molecule of a substance

Usually very small

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5
Q

How do you work out molecular mass

A

Molar mass/avocados constant

m=M/Na

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6
Q

Total number of atoms

A

N=n×Na

Moles×molecules in one mole

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7
Q

Total mass of a substance

A

Mtotal=n×M (moles×mass of one mole)

Mtotal=n×Na×m (moles×number of molecules in one mole×mass of one mole)

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8
Q

What 4 things is the physical condition or state of a gas describes by

A

4 state variables

Pressure
Volume
Temperature
Number of moles

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9
Q

SI unit for pressure

A

Pa

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10
Q

SI unit for Volume

A

m³

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11
Q

SI unit for temperature

A

K

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12
Q

SI unit for number of moles

A

mol

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13
Q

Pressure

A

The normal force exerted by a gas per unit area/per unit surface area over which the force acts

P=F/A

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14
Q

Volume

A

Space occupied by a gas, often correlating with the size of a container

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15
Q

Temperature

A

Measure of average maximum kinetic energy of molecules

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16
Q

A temperature of change of 1°C is a change of how many kelvin

A

1

Just use a different reference point

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17
Q

Celsius vs Kelvin

A

Celsius uses the freezing point of water as its zero point (water freezes at 0°C) and defines the billing point of water as 100°C

Kelvin uses absolute zero as its zero point (0K)

A change of 1 is the same for both

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18
Q

What is absolute zero

A

-273°C
0K
Particles motions associated with heat stop and an ideal gas exerts no pressure

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19
Q

Converting Celsius to kelvin

A

Tk=Tc+273

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20
Q

Room temperature

A

20°C

293K

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21
Q

Atmospheric pressure at sea level

A

101kPa

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22
Q

3 gas laws

A

Boyle’s
Charles’
Pressure/Gay-Lussac’s

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23
Q

Boyle’s Law

A

The pressure of a gas is inversely proportional to the volume
At a constant temperature and moles (molecules)

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24
Q

Isothermal

A

Constant temperature

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25
Q

Boyle’s Law equation

A

PV=constant

P1V1=P2V2

P1/P2=V2/V1

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26
Q

Explain the graph for Boyle’s Law (P,V)

A

P=y
V=x

Asymptotes at P=0 and V=0
Inversely promotional graph

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27
Q

Explain the graph for Boyles law (P,1/V)

A

Directly proportional
Straight line
Through origin

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28
Q

For any given volume, the pressure is higher if the temperature is…

A

Higher

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29
Q

For any given volume, the pressure is higher if the temperature is…

A

Higher

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30
Q

Charles’ law

A

Volume of gas is directly proportional to temperature at a fixed pressure and mass (moles)

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31
Q

Isobaric

A

Constant pressure

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32
Q

Do you use temperature in kelvin or celcius

A

Kelvin

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33
Q

Equations for Charles law

A

V=T×constant

V1/T1=V2/T2

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34
Q

Explain the graph for Charles law (Temp in kelvin)

A

V=y
T=x

Directly proportional
Straight line
Through origin

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35
Q

Explain the graph for Charles law (temp in celcius)

A

V=y
T=x

Straight line
Through x axis at -273
Crosses y axis at non zero value

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36
Q

For any given temperature, the volume of gas is higher at a …pressure

A

Lower

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37
Q

Pressure law

A

The pressure of a gas is directly proportional to the temperature
At a constant volume
And moles/molecules

38
Q

Isovolumetric

A

Constant volume

39
Q

Equations for the pressure law

A

P=T×constant

P1/T1=P2/T2

40
Q

Explain the graph for pressure law (temp in kelvin)

A

P=y
T=x

Directly proportional
Straight line
Through origin

41
Q

Explain the graph for pressure law (temp in celcius)

A

P=y
T=x

Straight line
Crosses x axis at -273
Crosses y axis at non zero value

42
Q

Equation and ratio for gas law

A

PV/T=constant

P1V1/T1 = P2V2/T2

In Kelvin
Moles constant

43
Q

Ideal gas equation

A

PV=nRT

n=number of moles
R=molar gas constant (formula sheet, 8.31JK-¹mol-¹)

44
Q

Where does the ideal gas equation come from

A

PV/T=constant

Since nR are constant, PV/T=nR
So PV=nRT

45
Q

What is the Boltzmann equation

A

An alternative form of the ideal gas equation

PV=NkT

46
Q

How is the Boltzmann equation formed

A

PV=nRT
n=N/Na

PV=RTN/Na

Boltzmann constant (k=1.38x10-²³JK-¹) = R/Na

So PV=NkT

47
Q

Why can you obtain another constant for the Boltzmann constant

A

k=R/Na

Both R and Na are constants

48
Q

5 assumptions for an ideal gas

A

Volume of a molecule is negligible compared to the volume occupied by the gas
The intermolecular forces of attraction between the molecules are negligible and only influence eachother during collision
The time between collisions with the container walls and other molecules is much greater than the duration of a collision
The collisions between molecules and collisions with walls of container are elastic
There are a large number of molecules, who’s motion is random

49
Q

Closest to an ideal gas

A

Helium

50
Q

Why is helium closest to an ideal gas

A

Monatomic so does not form a dipole
Closest to a point mass since a single atom molecule
Interacts weakly with other atoms as it has a full outer shell of electrons
Very low boiling point, 4K

51
Q

Aside from helium, when do other gases behave more like an ideal gas

A 
High temperatures (far above boiling point)
And low pressures (low density so molecules far apart)
52
Q

When and how was brownian motion first observed

A

By Robert brown

Noticed the apparent random motion of small pollen parti les suspended in water

53
Q

Explain brownian motion in terms of the pollen particle

A

Continously bombarded on all side by water molecules
At any given moment there may be slightly more collisions on one side
Or water molecules hitting the pollen may differ in speeds hence momenta
Giving a resultant force on pollen
So it accelerates in the direction of the resultant force
Because the direction and momentum of collision changes a short time later the resultant force may then be in a different direction

54
Q

Use the kinetic theory to explain boyles law when the volume of a container decreases

A

Fixed temperature so momentum change of each molecule the same
Time between collisions decreases
Shorter distance to walls
Increased number of collisions per second
Means total change in moment is greater
Larger force exerted on container walls (F=change in momentum/change in time)
Which means pressure increases since P=F/A

55
Q

Explain Charles law in terms of the kinetic theory when the temperature of a gas is increased

A

Average kinetic energy of molecules increases (move faster)
So change of momentum of each collision is greater
To keep the total force and pressure constant the volume increases
Increasing the time between collisions so pressure is constant

56
Q

Explain the pressure law in terms of the kinetic theory when the temperature of a gas increases

A

Average kinetic energy of molecules increases (move faster)
So change of momentum of each collision is greater
Volume is constant so the total force increases
Increasing the pressure exerted (P=F/A)

57
Q

Equation to calculate the speed of particles for kinetic theory and ideal gases

A

PV=1/3 (Nm(crms)²)

58
Q

Fusion

A

Liquid to solid

59
Q

Vaporisation

A

Liquid to gas

60
Q

Condensation

A

Gas to liquid

61
Q

Sublimation

A

Solid to gas

62
Q

Deposition

A

Gas to solid

63
Q

Specific latent heat of fusion

A

Energy required to change 1kg of substance from a solid into a liquid at its melting point

64
Q

Specific latent heat of vaporisation

A

Energy required to change 1kg of substance from a liquid into a gas at its boiling point

65
Q

Crms

r.m.s

A

Root mean square of speed

Average of the squares of the speeds of the molecules

66
Q

Root mean square speed

A

Speeds of particles are squared
Mean of squares is taken
Square root is taken

Deals with negatives since square before adding

67
Q

Average kinetic energy of a gas molecule in Joules

A

1/2m(crms)^2=3nRT/2N=3kT/2=3RT/2Na

68
Q

Units of crms

A

m^2s^-2

69
Q

Mean squared speed/(crms)^2

A

Speeds of particles are squared and a mean is taken

Quantity is related to the mean kinetic energy of gas molecules

70
Q

Explain the Maxwell-Boltzmann distribution curve

A

x=Speed in m/s
y=% of molecules with speed in range +/- 1m/s

As a gas gets hotter the peak (most probable speed) moves to the right and is lower and wider, meaning there are more molecules moving at a high speed and a greater range of speeds
Area stays the same since the number of molecules stays the same
Just fewer moving slowly

71
Q

Show that the kinetic energy of a gas molecule is proportional to the temperature

A

PV=1/3Nm(Crms)^2 and PV=NkT

NkT=1/3Nm(Crms)^2
kT=1/3m(Crms)^2
Substitute 1/3 for 2/3 x 1/2
2/3 x 1/2m(Crms)^2=kT
1/2m(Crms)^2=3/2kT

Since Ek=1/2mv^2, Ek=1/2(Crms)^2

Ek=3/2kT

Since 3/2k is a constant, Ek is proportional to T

72
Q

“Molecules of Helium-4 travel faster than Krypton-84”

Comment on this statement

A

rms speed is greater for helium than krypton so more (not all) molecules of helium are moving faster
there will still be some molecules of helium moving slower than some of krypton’s due to the Maxwell Boltzmann distribution curve

73
Q

Heat

A

The transfer of thermal energy from a substance to its environment
Q

74
Q

Internal energy

A

The thermal energy stored within a gas
For real gases this is the sum of the total kinetic and potential energies
For ideal gases this is the total kinetic energy only

75
Q

Where does the potential energy arise from in a real gas

A

The electrostatic forces between gas molecules

e.g dipole-dipole or van der waals

76
Q

Thermal equilibrium

A

No net energy transfer between them when they are placed in contact

77
Q

Explain energy transfer if two objects are at different temperatures

A

Object at a higher temperature will have a greater mean kinetic energy
If the two objects are placed in contact with each other then molecules from each will collide
During the collisions energy will be transferred from the molecules with a higher kinetic energy to the molecules in the lower temperature material with lower kinetic energy
This continues until the mean kinetic energies are equal
At this stage the two objects will have the same temperature and be in thermal equilibrium

78
Q

Specific heat capacity

A

The energy needed to raise the temperature of 1kg of a substance by 1K

79
Q

Why is water used as a coolant

A

It takes a lot of energy to heat mass of water by 1K than (context of question)
So it removes a large amount of energy as it comes into thermal equilibrium with the object its cooling

80
Q

Specific heat capacity equation

A

Q=mc△T

Q in joules
T in kelvin
c in Jkg^-1K^-1

81
Q

What values are negative when using the specific heat capacity equation for cooling a material

A

Change in temperature

Energy input, since energy neds to be removed from the system

82
Q

What materials are best for storing thermal energy

A

Things like water
With high specific heat capacities
So can store lots of energy with a small increase in temperature

83
Q

What is calorimetry

A

The study of energy changes in a system by measuring the heat exchanges with its surroundings

84
Q

Describe an experiment to measure the heat capacity of the liquid inside the calorimeter

A
  1. Measure the mass of the system with and without water using a balance
  2. Subtract the full from empty to get the mass of water
  3. Set up a circuit with a voltmeter, ammeter, cell and resistor so the resistor is in the water
  4. Insulate the beaker with bubble wrap
  5. Close switch
  6. Keep current, voltage and mass constant
  7. Measure and record temperature at regular intervals (e.g every minute) using a thermometer
  8. Plot a graph of time against change in temperature
  9. Gradient =
85
Q

Calculate the specific heat capacity if a p.d of 12V delivers a current of 1.2A for 70s to a sample of material of mass of 0.12kg resulting in a temperature change of 16K

A

c = Q/m△T

Q = Energy input in Joules = Power x Time (Pt)

P = IV = 1.2x12 = 14.4
Q = Pt = 14.4x70 = 1008

c = 1008/(0.12x16) = 525Jkg^-1K^-1

86
Q

Changing state equation

A

Q=ml

87
Q

Changing temp equation

A

Q=mc△T

88
Q

Specific latent heat of vaporisation or fusion equation

A

Q=ml

89
Q

Work done, pressure volume equation

A

W=P△V

90
Q

Constant pressure
Constant temperature
Constant volume

A

Isobaric
Isothermal
Isovolumetric

A Level Physics Paper 2 (7 decks)

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