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A-Level Physics - OCR A > M5, C1 Thermal Physics > Flashcards

M5, C1 Thermal Physics Flashcards

1
Q

how do particles behave in a solid

what happens when a solid is heated

A
  • strong forces of attraction between the particles - held close together
  • particles vibrate about fixed positions

When heated the particles gain energy and vibrate more. Eventually they may break away from the solid structure and become free to move around. When this happens, the solid has melted and become a liquid.

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2
Q

how do particles behave in a liquid

what happens when a liquid is heated

A
  • particles are free to move around
  • flows easily, has no fixed shape, irregular arrangement
  • there are still forces of attraction between the particles but they’re weaker than the ones in the solid

When heated, some of the particles gain enough energy to break away from the other particles.
The particles which escape from the liquid become a gas.

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3
Q

how do particles behave in a gas

A
  • particles are far apart
  • almost no forces of attraction between the particles (there are no forces of attraction in an ideal gas)
  • move in a rapid and random motion
  • occupies a much larger volume than a liquid
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4
Q

what is the kinetic model of matter or kinetic theory

A

the idea that solids, liquids and gases are made up of tiny moving or vibrating particles

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5
Q

when a substance changes phase/state, what happens to the internal energy, total kinetic energy and temperature

A

Internal energy - changes

Total kinetic energy - stay the same

Temperature - stay the same

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6
Q

Sketch a graph of time (x) against temp (y) of heating a beaker of ice until it reaches 100 degrees c

A

increases for first couple of minutes
stays the same at about 20°C for about 5 minutes
increases at a steady rate for 5 minutes up to 100°C
remains the same at 100°C for over 10 minutes

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7
Q

state what is meant by thermal equilibrium

A

If body A and body B are both in thermal equilibrium with body C, then body A and body B must be in thermal equilibrium with each other.

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8
Q

Thermal energy is always transferred from regions of _____ temperature to regions of ______ temperature.

A

higher => lower

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9
Q

What apparatus would you set up in order to observe the Brownian motion of smoke particles in air?

what would you observe

A

Using a smoke cell in glass block. Attached to power supply for light.
Fill with smoke and place cover slip over it.
Place under a microscope.

smoke particles appear as bright specks moving a rapid, random motion

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10
Q

what is Brownian motion proving

A

gas particles move in a rapid, random motion

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11
Q

what does the kinetic energy of a particle depend on

A

the particles mass and speed

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12
Q

what is the potential energy of a particle caused by

A

the interactions between particles and is based on their positions relative to each other

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13
Q

define internal energy

A

the sum of the random distribution of kinetic and potential energies associated with the molecules of a system

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14
Q

what is absolute zero

A 
0 kelvins (-273°C)
the lowest temperature possible

the minimum possible internal energy

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15
Q

How do you work out the temperature in kelvin if you have it in °C

A

ADD 273

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16
Q

what is 100°C in kelvin

A

100 + 273 =

373 K

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17
Q

in a heating curve graph for solids, what’s happening on the increasing parts
(Ek, Ep and internal energy)

A 
Thermal energy is going into increasing the vibration of the molecules in the state.
Kinetic energy increases.
Potential energy constant.
Internal energy increases.
1st increasing line = solid
2nd increasing line = liquid
3rd increasing line = gas
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18
Q

in a heating curve graph for solids, what’s happening on the straight horizontal line parts
(Ek, Ep and internal energy)

A

Change of state.
1st line = melting = energy used to weaken the forces of attraction between molecules.
2nd line = evaporation = energy used to break the forces of attraction between molecules.

kinetic energy constant
potential energy increasing
internal energy increasing

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19
Q

On the heating curve graph why is the second horizontal line longer than the first

A

The second line is evaporation which means the energy is used to break the forces of attraction which requires a lot more energy than melting (the first line) which only weakens the forces of attraction.

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20
Q

define specific heat capacity

A

The specific heat capacity of a substance is the amount of energy needed to raise the temperature of 1kg of the substance by 1K or 1°C

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21
Q

what does the equation E = mc∆θ mean

A

energy = mass X specific heat capacity X change in temperature

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22
Q

The specific heat capacity of water is 4180Jkg^-1K^-1.

If 172kJ of energy is supplied to 5kg of water at 300K, what will its final temperature be?

A

∆θ = E / mc
= 172X10^3 / (5X4180) = 8.229K

final temp = 300 + 8.229 = 308.229

= 308K

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23
Q

Plan an investigation to find a value of specific heat capacity of a material

A

Get your material with an electric heater and thermometer inside.
Measure the mass of the substance and its intitial temperature.
Set up a circuit with an ammeter and voltmeter attached to the heated material.
Every minute, record the temperature, current and voltage.
Calculate the energy by using the equation E = VIt.
Plot a graph of energy (x) against temperature (y).
The gradient of the graph will be 1/mc. Calculate c.

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24
Q

define specific latent heat of fusion/vaporisation

A

the quantity of thermal energy required to change the state of 1kg of a substance

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25
Q

what does the equation E=mL mean

A

energy change = mass X specific latent heat

26
Q

what are the units of specific latent heat of fusion/vaporisation

A

Jkg^-1

27
Q

plan an experiment to determine the specific latent heat of fusion of ice

A

1) Connect an electric heater to an ammeter and a voltmeter
2) Put equal masses of ice in 2 identical funnels above beakers
3) Put the heater into one of the funnels for 3 mins (use stopwatch). measure the current and voltage at the start too. Calculate the energy using E=VIt
4) At the end of the 3 mins, measure the mass of water collected in the beakers.
5) Subtract the mass of water collected from the unheated funnel from the mass of water collected from the heated funnel. This gives the mass of ice that melted solely to due to the presence of the heater.
6) use L = E/m to calculate the latent heat of fusion

28
Q

plan an experiment to determine the specific latent heat of vaporisation of water

A

1) Place insulation around the outside of a small beaker, but leave the top of the beaker open to the air
2) Fill the beaker part-way up with water
3) Connect a voltmeter and an ammeter to an electric heater and put in water.
4) Place the beaker on a balance and switch heater on.
5) Once the water is boiling, record the mass on the balance and start the timer
6) Measure the voltage and current
7) When the mass has decreased by about 15g, stop the timer and turn heater off.
8) Record the new mass of the beaker and its contents and subtract from original mass
9) Calculate the energy transferred by the heater to the water by E=VIt
10) Then use L = E/m to determine the specific latent heat of vaporisation of water.

29
Q

on the heating curve graph, what parts show the specific latent heat of fusion and vaporisation

A

the straight lines

solid to liquid / liquid to solid is fusion

liquid to gas / gas to liquid is vaporisation

30
Q 
Calculate the energy required to boil 2kg of ice initially at -40 degrees and determine the percentage of this energy required to change the phase of the water from liquid to gas.
c of ice = 2 X10^3 Jkg^-1K^-1
L of ice = 3.3 X 10^4 Jkg^-1
L of water = 2.26 X 10^6 Jkg^-1
c of water = 4200 Jkg^-1degrees^-1
A

4 stages - need to find energy to change the temperature and then change the state

1) E = 2 X 2X10^3 X 40 = 1.6X10^5 J
2) E = 2 X 3.3X10^4 = 6.6X10^4 J
3) E = 2 X 4200 X 100 = 8.4X10^5 J
4) E = 2 X 2.26X10^6 = 4.52X10^6 J

Add them all up
E = 5.586X10^6 J

percentage =

(4.52X10^6 / 5.586X10^6) X 100 = 81%

31
Q

what experiment could you do to investigate Boyle’s law

A
  • Have a sealed tube containing oil
  • Use a tyre pump to increase the pressure of the oil
  • Use a Bourdon gauge to record the pressure. As pressure increases, more oil will be pushed into the tube so the oil level rises. The volume of air reduces.
  • Increase the pressure until the oil is at the top and in set intervals let the pressure drop so the oil level falls by 1cm^3 each time
  • At each interval, record the pressure and volume of oil in the tube.
  • Plot a graph of pressure against 1/V. It should give a straight line.
32
Q

what is boyle’s law in words

A

at a constant temperature, the pressure and volume of an ideal gas are inversely proportional

33
Q

what is boyle’s law in an equation

A

p is inversely proportional to volume

so

pV = constant
at a constant temperature

34
Q

A container is divided at the centre with gas on one side and a vacuum on the other side.
The gas is contained at a pressure of 350kPa. The divider is then removed so the gas fills the whole container.
Calculate the new pressure of the gas, assuming that the temperature of the gas remains constant.

A

pV = constant
so p1V1 = p2V2

When the divider is removed, the volume containing the gas is now twice as big so V1 / V2 = 0.5

p2 = 350000 X 0.5

=175000 = 175 kPa

35
Q

The pressure law states that at constant volume, the pressure of an ideal gas is directly proportional to its absolute temperature. What equation can you determine from this

A

p/T = constant

TEMPERATURE HAS TO BE IN KELVIN

36
Q

Draw 2 graphs of pressure (y) against temperature (x) one of which is in degrees Celsius, and one in Kelvin demonstrating the pressure law

A

both straight positive lines

for degrees Celsius, the line crosses -273 on the x axis

for Kelvin, the line crosses the origin on the x axis

37
Q

Charles’ law states that V/t = constant when the pressure is constant in an ideal gas.
Using this, Boyle’s law and the pressure law, determine a larger equation.

A

pV / T = constant

p1V1 / T1 = p2V2 / T2

38
Q

What is Avogadro’s constant

A

the number of particles in one mole

39
Q

What equation can you use to calculate the number of particles in an amount of gas

A

number of particles = number of moles X Avogadro’s constant

N = n X N_A

n is measured in mol

40
Q

derive the equation for pV = nRT

A 
pV / T = constant
pV = constant X T
The molar mass constant is R.
The amount of gas is measured in moles, n, so the constant in the equation becomes nR where n is the number of moles of gas present.
therefore
pV = nRT
41
Q

derive the equation for pV = NkT

A 
The Boltzmann constant is given by:
k = molar mass constant / Avogadro's constant
combine with Avogadro's constant = N/n
k = R / (N/n) = nR / N
nR = Nk
substitute into pV = nRT
so
pV = NkT
42
Q

what equation could you use to calculate molecular mass

A

molecular mass = mass / number of moles

43
Q

the molar mass of oxygen is 32gmol^-1

calculate the mass of 1 molecule of oxygen

A

32 / Avogadro’s constant
= 32 / 6.02 X10^23
= 5.32 X10^-23 g

44
Q

Calculate the pressure inside a helium gas cylinder which has a volume of 0.2m^3 that contains 50 moles of gas at the temperature 20 degrees C.

A

temperature = 20 + 273 = 293K
p = nRT / V
= 50 X 8.31 X 293 / 0.2
= 6.1 X10^5 Pa

45
Q

what do all the parts of this equation mean and give units

pV = nRT

A 
p = pressure in Pa
V = volume in m^3
n = number of moles of gas
T = temperature in Kelvin
R = molar mass constant (in equation sheet)
46
Q

what do all the parts of this equation mean and give units

pV = NkT

A 
p = pressure in Pa
V = volume in m^3
N = number of molecules of gas
T = temperature in kelvin
k = Boltzmann constant (in equation sheet)
47
Q

List all the assumptions made if the kinetic theory of the properties of gas

A
  • the gas contains a large number of particles
  • the particles move rapidly and randomly
  • the volume of the particles is negligible when compared to the volume of the gas
  • collisions between particles themselves or between particles and the walls of the container are perfectly elastic
  • the duration of each collision is negligible when compared to the time between collisions
  • there are no forces between particles except for the moment when they are in a collision
48
Q

what does the pressure exerted by a gas depend on

A
  • the volume of the container (increasing the volume, decreases the frequency of collisions, pressure decreases)
  • the number of particles (more particles means more collisions mean force increases)
  • the mass of the particles (heavier particles exert a greater force)
  • the speed of the particles (faster particles hit the walls, greater the change in momentum and force exerted)
49
Q

what does this equation mean

pV = 1/3(Nm)

A 
p = pressure
V = volume
N = number of particles of gas
 = mean square speed of gas particles m^2s^-2
m = mass of gas particles
50
Q

what is the mean square speed

what is the root mean square speed

A

mean square speed if the average of the squared speeds of all the particles so the square root of it gives you the typical speed (root mean square speed or rms speed)

51
Q

61 moles of a gas are enclosed in a 0.75m^3 container. If the pressure in the container is 101 kPa and each particle has a mass of 2.65X10^-26kg, calculate the mean square speed of the gas particles.

A

pV = 1/3(Nm)

N = 61 X 6.02X10^23
sub in equation and rearrange for

= 2.34 X10^5 m^2s^-2

52
Q

Five molecules have the speeds of 450, 500, 450, 400 and 600 ms^-1.
Calculate their mean square speed.

A

you have to square them all individually and divide by how many there are

(450^2 + 500^2 + 450^2 + 400^2 + 600^2) / 5

= 235,000 m^2s^-2

53
Q

Five molecules have the speeds of 450, 500, 450, 400 and 600 ms^-1.
Calculate their mean square speed.

A

you have to square them all individually and divide by how many there are

(450^2 + 500^2 + 450^2 + 400^2 + 600^2) / 5

= 235,000 m^2s^-2

54
Q

what’s another way to write the equation pV = 1/3(Nm) but use density instead

A

the total mass of the gas = Nm
volume = V

density = mass / volume
= Nm / V

so

p = 1/3 X density X mean square speed

55
Q

at normal room temperature, the density of air is 1.2 kgm^-3. If the average molecular speed speed if 500ms^-1. Calculate the pressure of the air.

A

pV = 1/3(Nm)
but Nm/V = density

p = 1/3 X 1.2 X 500^2

= 1X10^5 Pa

56
Q

draw a graph for the Maxwell-Boltzmann distribution

A

y axis - number of molecules
x axis - kinetic energy or particle speed

Relatively few molecules are moving slowly or quickly.
Most molecules are moving at the average speed.

57
Q

what happens to the Maxwell-Boltzmann distribution graph as temperature increases

A
  • average particle speed increases

- the graph shifts to the right and the peak becomes lower

58
Q

derive an equation for E = 3/2 kT

A

pV = NkT and pV = 1/3 Nmc^2

NkT = 1/3 Nmc^2
kT = 1/3 mc^2
mc^2 = 3kT

multiply by 0.5

1/2mc^2 = 3/2 kT
E = 3/2 kT
59
Q

In an ideal gas the potential energy is ___ because ______.

This means that the internal energy is equal to the __________________ only.

A

In an ideal gas the potential energy is 0 because there are no forces between the particles.
This means that the internal energy is equal to the total random kinetic energy only.

60
Q

Derive an equation for the internal energy of an ideal gas.

A

U = 3/2 NkT

because you multiply the energy by the number of gas particles (3/2kT X N) to get an equation for internal energy

61
Q

What can be concluded about the average kinetic energy of a gas and absolute temperature

A

Average kinetic energy is directly proportional to the absolute temperature.
So a rise in absolute temperature cause an increase in the kinetic energy of the particles, meaning a rise in internal energy.

62
Q

The mass of 2 moles of nitrogen is 56g. Calculate the total kinetic energy of nitrogen at 20 degrees celcius.

A

20 degrees = 293 K
for total kinetic energy use E = 1.5NkT
N = 2 X 6.02X10^23

E = 1.5 X 1.38X10^-23 X 293 X 2 X 6.02X10^23

= 7302J
=7.3 kJ

A-Level Physics - OCR A (20 decks)

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