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OCR A-Level Physics > 5.1 Thermal Physics > Flashcards

5.1 Thermal Physics Flashcards

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1
Q

what is an absolute or thermodynamic scale of temperature?

A

an absolute or thermodynamic scale of temperature is independent of the properties of any specific substance, measured in kelvin

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2
Q

how do you convert from degrees to kelvin?

A

(degrees value) +273

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3
Q

how do you convert from kelvin to degrees?

A

(kelvin value) -273

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4
Q

what is the triple boiling point of water? and what is it roughly in degrees?

A

the temperature at which water can exist as a solid, liquid or gas (around 0.01 degrees)

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5
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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6
Q

why can you not ever have absolute zero?

A

nothing can have 0 internal energy

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7
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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8
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, high density (low mean separation)
  • very strong intermolecular forces
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9
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
  • mean separation is greater than solids (less dense)
  • less strong intermolecular forces
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10
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 attractive forces except during collisions
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11
Q

what is the defintion of brownian motion?

A

the random movement of small visible particles suspended in a fluid due to collisions with much smaller, randomly moving atoms or molecules of the fluid

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12
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 from side to side, and up and down
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13
Q

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

A
  • jerky, random movement due to the collisions with air particles meaning air particles are constantly moving
  • amir 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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14
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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15
Q

what is the relationship between average KE and temperature?

A

average KE is proportional to temperature

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16
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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17
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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18
Q

what is the total internal energy equation?

A

kinetic energies + potential energies

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19
Q

what is thermal energy?

A

the component of a body’s internal energy due to its temperature, thermal energy can be supplied to a body by heating it

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20
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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21
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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22
Q

if you increase the temp. of something what happens to the internal energy?

A

because the KE increases, the internal energy also increases

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23
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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24
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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25
Q

what are the units for specific heat capacity?

A

JKg-1K-1

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26
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

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27
Q

outline an experiment to determine specific heat capacity

A
  • put an electric heater in a liquid and fully submerge it along with a thermometer
  • wrap the container of liquid with an insulator and use a lid to prevent heat loss to surroundings
  • you can stir the solution for even heating
  • to work out c use E = mcΔϴ and equate this energy to the energy in the power equation (E = power x time)
  • power = IV so energy = IVt
  • IVt = mcΔϴ so work out c by using c = IVt / mΔϴ
28
Q

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

A

flattens the curve and the peak spreads out as the AREA UNDER THE CURVE IS FIXED, more molecules posses a higher average speed

29
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

30
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

31
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
32
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

33
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

34
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>

35
Q

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

A
  • put a heating coil/electric heater and equal masses of ice in two funnels above beakers
  • turn on one coil for 3 mins, record the energy transferred in the 3 mins using P = IV and P = E / T
  • don’t turn on the other coil - 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
36
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

37
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)
38
Q

what is Avogadro’s constant?

A

6.02 x 10^23

39
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

40
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

41
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
42
Q

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

A

pressure = force / area (measured in pascals)

43
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)

44
Q

what causes pressure? how does it work?

A

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

45
Q

what are the 3 gas laws?

A
  • Boyle’s Law
  • Charles’s Law
  • The Pressure-Temperature Law
46
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)

47
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

48
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

49
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
50
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

51
Q

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

A

straight line because they have a directly proportional relationship

52
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

53
Q

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

A

straight line because they have a directly proportional relationship

54
Q

what is always kept constant in all 3 gas laws?

A

mass of the gas

55
Q

how do you remember the 3 gas laws?

A

remember order of laws, 1/2/3
1 - temp constant
2 - pressure constant
3 - volume constant

56
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
57
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)

58
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
59
Q

what is the mean square speed?

A

the mean square speed is the mean value of the square of velocity c for a large number of gas particles (atoms or molecules) moving randomly in a gas

60
Q

what is the root mean square speed (r.m.s)? and what does it tell you?

A

it is the square root of the mean square speed, it gives you the ‘typical’ speed of a particle in kinetic theory

61
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
62
Q

what is the Boltzmann constant?

A

the Boltzmann constant, k, is a constant used when relating the temperature of the gas to the mean translational kinetic energy of the particles in the gas, it can also be thought as the gas constant for a single molecules

63
Q

when do you use pV = nRT and pV = NKT?

A 
pV = nRT ---> for moles (n)
pV = NKT ---> for no. of atoms/molecules (N)
64
Q

what is the Boltzmann constant equal to?

A

k = R / Avogadro’s constant

65
Q

what two equations can you equate to show the relationship between the mean kinetic energy of a molecule of mass m, the mean square speed and the absolute temp?

A

0.5mc^2bar = 3/2kT

66
Q

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

A

they are directly proportional

67
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

OCR A-Level Physics (24 decks)

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