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SAJID OCR A-Level Physics > 5.1 Thermal Physics > Flashcards

5.1 Thermal Physics Flashcards

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1
Q

What is the triple point of pure water

A

One specific temp and pressure where the three phases of matter coexist in thermal equilibrium

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2
Q

how do you convert from degrees to kelvin?

A

(degrees value) +273

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3
Q

The pressure and temp of the triple point of pure water

A
  1. 01 degrees

0. 61kpa

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4
Q

how do you convert from kelvin to degrees?

A

(kelvin value) -273

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5
Q

Explain the net flow of thermal energy

A

Net flow of energy will flow from the hotter object to the colder one

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6
Q

State the fixed point on the absolute Scale of water

A

Absolute zero

Triple point of pure water

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7
Q

what is absolute zero?

A

absolute zero (0K) is the theoretical temperature at which a substance has MINIMAL INTERNAL ENERGY

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8
Q

State the values of minimum internal energy

A

the kinetic energy of all the atoms or molecules is zero - they have stopped moving.

However,
the internal energy is not zero because the substance still has electrostatic potential energy stored between the particles.

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9
Q

what are the two fixed points on a Celsius scale and why is this scale not perfect

A
  • Freezing point of pure water
  • boiling point of pure water

not perfect because the fixed points vary significantly depending on the surrounding atmospheric pressure

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10
Q

why can you not ever have absolute zero?

A

nothing can have 0 internal energy

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11
Q

what is thermal equilibrium?

A

objects in contact with each other at the same temp. are in thermal equilibrium, this means that there is no heat flow (net energy transfer) between them

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12
Q

what is the motion of particles, spacing of particles and forces acting on particles in a solid?

A
  • particles vibrate about fixed points
  • particles very close together in a regular three dimensional structure, high density (low mean separation)
  • very strong electrostatic forces of attraction
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13
Q

what is the motion of particles, spacing of particles and forces acting on particles in a liquid?

A
  • particles can slide past each other, free to move around, has no fixed shape
  • mean separation is greater than solids (less dense)
  • less strong electrostatic forces of attraction
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14
Q

what is the motion of particles, spacing of particles and forces acting on particles in a gas?

A
  • random, rapid motion in all directions
  • high mean separation, particles not close together, not dense
  • virtually no forces of attraction between them except during collisions
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15
Q

how did Brown discover brownian motion in 1827? how can you observe brownian motion in a lab?

A
  • put some smoke in a brightly illuminated glass jar and observe the particles using a microscope
  • the smoke particles appear as bright specs moving haphazardly caused by the air molecules constantly striking the smoke particles.
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16
Q

what were the observations and conclusions from the brownian motion seen during the experiment?

A
  • jerky, random haphazard movement due to the collisions with air particles meaning air particles are constantly moving
  • air molecules cannot be seen by the naked eye meaning they must be very small
  • there must be a large number of particles
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17
Q

what is internal energy defined as?

A

internal energy is defined as the sum of the randomly distributed kinetic and potential energies of all atoms or molecules within a system

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18
Q

what temperature does ice melt

A

Ice melts at 0 degrees

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19
Q

What temperature does water boil

A

100 degrees

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20
Q

what is the relationship between average KE and temperature?

A

average KE is proportional to temperature

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21
Q

what does kinetic energy relate to/represent?

A

due to the movement, in the form of vibrational motion (dependent on the mass and velocity of particles)

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22
Q

what does potential energy relate to/represent?

A

stored in the bonds and the inter-molecular forces of attraction (measured by the mean separation of the particles)

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23
Q

what is the total internal energy equation?

A

kinetic energies + potential energies

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24
Q

what is thermal energy?

A

Thermal energy is the internal energy of an object due to the kinetic energy of its atoms and/or molecules

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25
Q

what are on the axis of the Maxwell-Boltzmann distribution curve?

A

molecular speed on the x axis

no. of molecules with that speed on the y axis

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26
Q

where must all the lines start on a Maxwell-Boltzmann distribution curve?

A

the lines must start from zero because no molecules have zero energy

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27
Q

Describe the relationship between internal energy and temperature

A

If temperature increases, kinetic energy increases and therefore internal energy always increases

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28
Q

if you supply thermal energy to an object but its temp. remains constant what is happening?

A

its potential energy increases, KE stays the same (the speed of the molecules stays roughly the same)

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29
Q

what is the definition for specific heat capacity?

A

the specific heat capacity, c, of a substance is the amount of energy needed to raise the temperature of 1kg of a substance by 1 kelvin (or 1 degree celius)

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30
Q

what are the units for specific heat capacity?

A

JKg-1K-1

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31
Q

what is the equation for change in thermal energy?

A

E = mcΔϴ
where E = the change in thermal energy
c = specific heat capacity
Δϴ = change in temperature in K or degrees

32
Q

outline an experiment to determine specific heat capacity

A
  • measure the mass of the object using a mass balance and then put an electric heater in a liquid and fully submerge it along with a thermometer
  • make sure the material is insulated to ensure minimal heat is exchanged with the surrounding and measure the initial temperature
  • stir with thermometer so even heat is exchanged
  • Q = mc dtT
    Pt = mc dtT
    VIt = mc( Tf - Ti)
    Tf = VI/mc + Ti
  • Turn on the heater, record the pd and current and measure the temp every 30s
  • plot a graph of temp against time and fine the gradient
  • gradient = VI/mc
  • c = VI/m x gradient
33
Q

what does increasing the temperature do to the Maxwell-Boltzmann distribution curve?

A

Curve shifts to the right and the peak drops

AREA UNDER THE CURVE IS FIXED, more molecules posses a higher average speed

34
Q

what does a straight line (of 0 gradient) mean on a time of heating/temp graph?

A

the object is changing phase e.g water melting or boiling

35
Q

what does a line (of constant positive gradient) mean on a time of heating/temp graph?

A

the object isn’t changing phase, KE of molecules increases

36
Q

outline an experiment to determine the specific heat capacity of a metal block using the method of mixtures

A
  • heat a metal block of known mass, Mb, up to a temp Tb
  • quickly transfer this block into a container containing a mass of water, Mw, at a temp Tw
  • the hot block will heat the water, measure the temp of the water once is has reached a steady value Ts (reached equilibrium)
  • the heat energy gained by the water is equal to the heat lost by the block so MwCwΔϴw = MbCbΔϴb
  • for Δϴ always use (T2 - T1) but remember to minus the side that has LOST energy
37
Q

what is the definition for specific latent heat of fusion?

A

the amount of energy required to change the phase or state of 1kg of a substance from a solid to a liquid

38
Q

what is the definition for specific latent heat of vaporisation?

A

the amount of energy required to change the phase or state of 1kg of a substance from a liquid to a gas

39
Q

what is the equation for specific latent heat of fusion/vaporisation?

A

E = mL
where m = mass of the substance
(the larger the mass of the substance the more energy it takes to change the state>

40
Q

outline an experiment to measure the specific latent heat of a solid or liquid

A
  • add an equal masses of ice in two funnels above beakers
  • then submerge an electrical heaters in the each content of ice
  • now you have a control and experimental experiment
  • a thermometer is used to identity when the ice is just about to melt
  • then turn on one electrical heater for 3 mins for experimental, record the energy transferred in the 3 mins using Lf E/ m , Pt / m = itv / m
  • don’t turn on the other heater- it’s there to act as a control so you can measure how much ice melts due to the ambient temp. of the room
  • at the end of the 3 mins measure the mass of the water collected in both beakers, subtract one by the other to get the ice that melted due to the electrical input then use E = mLf
41
Q

what is one mole?

A

one mole of any substance is the amount of substance that contains as many particles as exactly 12g of carbon-12, one mole of a substance will contain 6.02 x 10^23 particles

42
Q

Why do we carefully stir the liquid in a calorimeter

A

To ensure the content has uniform temperature throughout

43
Q

what is the equation for no. of particles or molecules?

A 
N = n x NA
where N = no. of particles
n = no. of moles
NA = Avogadro constant
(be careful with big N and little n)
44
Q

what is Avogadro’s constant?

A

6.02 x 10^23

45
Q

what is an ideal gas?

A

an ideal gas is a gas that has internal energy only in the form of RANDOM KINETIC ENERGY

46
Q

when do real gases will behave like an ideal gas?

A

real gases will behave like an ideal gas if they are at low pressure and a temperature significantly above their boiling point

47
Q

what are the five assumptions when modelling the behavior of an ideal gas?

A
  • the gas contains a large number of molecules in rapid, random motion
  • all collisions are elastic (KE is conserved)
  • negligible forces between particles except during collisions
  • the time for a collision to happen is negligible compared to the time between collisions
  • the particles occupy negligible volume compared to the volume of gas
48
Q

what is the formula for pressure? and what is the units?

A

pressure = force / area (measured in pascals)

49
Q

what is the value of atmospheric pressure?

A

around 100kPa, or 100,000 Pa (the reason you are not crushed due to this pressure is that there is an equal and opposite pressure inside your body, acting outwards, so the forces are balanced)

50
Q

what causes pressure on a container? how does it work?

A

So a gas in a container exerts pressure on the container walls due to collisions of gas molecules with the container walls

51
Q

what are the 3 gas laws?

A
  • Boyle’s Law
  • Charles’s Law
  • The Pressure-Temperature Law
52
Q

what is Boyle’s Law?

A

the volume of a fixed mass is inversely proportional to the pressure exerted on the gas, under conditions of CONSTANT TEMPERATURE
pV = constant (p1V1 = p2V2)

53
Q

what does a pressure/volume graph look like (Boyle’s Law)? and at different temperatures?

A

inverse square, curve with decreasing gradient, the higher the temp the further away the curve from the origin

54
Q

what does a pressure/ (1/volume) graph look like? and at different temperatures?

A

graph with line with constant positive gradient, at higher temps the gradient gets steeper

55
Q

outline an experiment to investigate Boyle’s law

A
  • you can investigate the effect of pressure on volume by setting up a pump connected to a air pipe to a tube with oil in it
  • the oil confines a parcel of air in a sealed tube with fixed dimensions, a tyre pump is used to increase the pressure, as the pressure increases the air will compress and the volume occupied by air in the tube will reduce
  • measure the volume of air when the system is at atmospheric pressure, then gradually increase the pressure noting down both the pressure and the volume of air, multiplying them together at any point should give a constant
56
Q

what is Charle’s law?

A

the volume v of a gas is directly proportional to its absolute temperature, T, at CONSTANT PRESSURE
V / T = constant

57
Q

what does a volume/temp pressure look like? (Charle’s Law)

A

straight line because they have a directly proportional relationship

58
Q

what is the pressure-temperature law?

A

the pressure of a gas is directly proportional to its absolute temperature, T, at CONSTANT VOLUME
P / T = constant

59
Q

what does a pressure/temp pressure look like? (pressure-temp law)

A

straight line because they have a directly proportional relationship

60
Q

what is always kept constant in all 3 gas laws?

A

mass of the gas

61
Q

outline an experiment to investigate pressure and temp of a gas at constant volume and how you can determine a value for absolute zero

A
  • as you want to keep VOLUME constant, heat a fixed mass of gas in a sealed flask at constant volume
  • the flask is placed in a water bath which is heated to different temperatures and the pressure at different temps. is recorded by looking at the reading on the pressure gage
  • plot a graph of pressure against temp. and either extrapolate the line back to give a rough estimation of absolute zero (where the line crosses the x axis) or work out the equation of the line (y = mx + c) and make y = 0
  • note that the thermometer should not touch the sides of the container, make the water fully touch the entire flask but that the flask doesn’t touch the bottom of the beaker
62
Q

if you combine all 3 gas equations what do you get?

A

pV / T = constant (this constant is dependent on the amount of moles used)

63
Q

what is the ideal gas equation?

A 
pV = nRT
where p = pressure in pascals
V = volume of gas in m^3
R = molar gas constant
T = absolute temp of gas in kelvin
64
Q

what is the equation that links pressure and volume to speed of the particles?

A 
pV = 1/3 Nmc^2bar
where p = pressure of gas in pascals
V = volume of gas in m^2
N = number of particles
m = mass of the particles
c = speed of the particles
65
Q

what is the Boltzmann constant equal to?

A

k = R / Avogadro’s constant

66
Q

Derive this equation 0.5mc^2bar = 3/2kT

A

Pv=1/3Nmc^2bar

pV=NkT

67
Q

Describe an experiment to use an electrical method to determine specific heat capacity

A
  • measure the mass of the object using a mass balance
  • make sure the material is insulated to ensure minimal heat is exchanged with the surrounding and measure the initial temperature
  • Q = mc dtT
    Pt = mc dtT
    VIt = mc( Tf - Ti)
    Tf = VI/mc + Ti
  • Turn on the heater, record the pd and current and measure the temp every 30s
  • plot a graph of temp against time and fine the gradient
  • gradient = VI/mc
  • c = VI/m x gradient
68
Q

what is the relationship between mean kinetic energy and the absolute temp for a molecule?

A

they are directly proportional

69
Q

what conclusions can we make from an ideal gas having mean kinetic energy directly proportional to its temp?

A

because an ideal gas has energy only in the form of of kinetic energy we can say internal energy of a gas is directly proportional to its absolute temperature

70
Q

Describe how the speeds of particles in a gas change as the temperature of the gas increases and also draw a maxwell distribution curve

A

Particles gain kinetic energy as the temperature increases
Therefore the speeds of the particles increases

Draw a maxwell graph

71
Q

Explain why there is less He that an O2 in the atmosphere

A

Both O2 and He have the same average KE, despite there different masses. However, the r.m.s speed will be different.

Which explains why there is less He than O2, and this because He atoms have very small mass, which in turn means higher r.m.s speeds.

Now according to maxwell distribution, some He atoms have greater speeds than the r.m.s. Given there high speed there able to escape the earths atmosphere. We call this velocity escape velocity

72
Q

The escape velocity for earth is around

A

11kms-1

73
Q

Explain the internal energy of an ideal gas

A

The internal energy of a gas is the sum of the randomly distributed KE and PE of the particles inside a gas. One of the assumptions of ideal gas states that the electrostatic forces between particles is negligible except during collisions. This means there is not electrical potential energy in an ideal gas. All the internal energy is the form of the kinetic energy of the particles. Doubling the temp on an ideal gas doubles the KE and therefore doubles the Internal energy

74
Q

Show a y = mx + c relationship with pV=nRt

A 
pV = nR x T 
Y   = m  .  x + c 
y = pV 
m = nR 
x = T
75
Q

Isothermic =

A

Temp constant

76
Q

Combing the gas laws equation

A

pV/T = constant

P1V1/T1=P2V2/T1

77
Q

Derive pV=NkT

A

K=R/Na

pV=nRT to give pV = nkNaT

pV=NkT

SAJID OCR A-Level Physics (25 decks)

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