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Aqa Physics > Thermal Physics - > Flashcards

Thermal Physics - Flashcards

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1
Q

What is absolute temperature ?

A

The temperature where the particles have no kinetic energy. Given by the value of 0k

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2
Q

How to convert from kelvin to Celsius ?

A

K - 273 = degrees Celsius

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3
Q

What is the molecular mass ?

A

The sum of the masses of all the atoms that make up a single molecule- example h2o

21 +116 = 18
2 hydrogen and one oxygen

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4
Q

What is avogadro’s constant ?

A

The number of molecules within a mole. (Na)
6.023 * 10 ^ 23

(Carbon 12 isotope - number of atoms within exactly 12 grams of an isotope )

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5
Q

What does 1 mole of a substance mean ?

A

It is a substance containing Na number of atoms.

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6
Q

What is the equation linking the number of atoms and the number of moles ?

A

N = n* Na

N - number of molecules or atoms
n - number of moles

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7
Q

What is the molar mass ?

A

It is the mass of 1 mole of a substance = the molecular mass

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8
Q

Give the relationship between the mass of a substance and the number of moles

A

Given that M is the mass of 1 mole

The mass of the substance (m) = Mn

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9
Q

Give the relationship between the number of moles and the atoms/ particles in the substance .

A

Number of atoms in the substance (N) = n*Na

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10
Q

Give the relation between the number of atoms in a substance and the mass of the substance.

A

N (no of atoms ) = (m/n) * Na = n*Na

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11
Q

What are the conditions/assumptions of ideal gases ?

A
  • gas particles are point masses (same mass + spherical )
  • average kinetic energy is directly proportional to the absolute temperature
  • particles move in constant random motion
  • follow newtons laws
  • have a negligible volume compared to the container
  • the collisions are elastic
  • the motion of the particles are straight
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12
Q

What does Boyles law state ?

A

At a constant temperature the pressure of a fixed mass of gas is inversely proportional to its volume

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13
Q

What is the equation to find a missing value ( boules law ) ?

A

P1V1 = p2 v2

As p*v = a constant

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14
Q

What does Charles law state ?

A

At a constant pressure , the volume of a fixed mass of gas is directly proportional to its absolute temperature

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15
Q

What is the equation to find a missing value ( Charles law ) ?

A

V1 / t1 =v2 / T2
As v/t is a constant

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16
Q

What does the pressure law state ?

A

At a constant volume, the pressure p of a fixed mass of gas is directly proportional to its absolute temperature

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17
Q

What is the equation to find a missing value ( pressure law ) ?

A

P1/ T1 = P2 /T2

As p/t is a constant

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18
Q

At a constant temperature why is there greater pressure when the volume decreases ?

A
  • when the volume is decreased the particles are closer together so collide with each other and the walls more frequently with force producing a greater pressure
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19
Q

Why does the volume increase when the temperature increases at a constant pressure ?

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A

As the temperature increases the particles gain more faster / move further apart taking up a greater volume

20
Q

What is an isobaric change ?

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A

A change where the pressure is kept constant

21
Q

How can you change the volume of a gas at a constant pressure ?

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A

Work has to be done ( transferring heat energy ) by heating

22
Q

What is the equation linking the work done and the pressure and volume ?

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A

Work done = pressure times change in volume

23
Q

Why does the pressure increase as the temperature increase at a constant volume ?

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A

As the temperature increases the kinetic energy of the particles increase causing them to travel at a faster speed colliding more frequently with a greater force producing a greater pressure

24
Q

What is the equation you get from combining the three gas laws ?

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A

PV/ T = R ( one mole )

Pv = nRT (n moles )

25
What is the constant for 1 mole of a (ideal ) gas at room temperature and atmospheric pressure ?
R = 8.31
26
How can the ideal gas equation be written in terms of the number of molecules in the gas ?
PV = NRT / Na ( n is replaced with N/Na) Which can be written as PV = NKT K is Boltzmann’s constant - R/Na
27
What is Brownian motion ?
The random motion of larger particles in a fluid due to collisions from the surrounding fluid particles. For example pollen grains colliding with water molecules.
28
What is an example of Brownian motion ?
Smoke particles being pushed around due to the smaller air molecules
29
What does the Maxwell Boltzmann distribution convey ?
The graph shows that the speeds of the molecules vary in speed ( all are not the same speed )
30
What does the area under the Maxwell Boltzmann graph give ?
The number of particles
31
What happens to the maxwell distribution if the temperature increases ?
The peak would shift to the right and would have a greater range producing a lower curve
32
What is the root mean square speed ? ( crms)
The root of the mean of the speed squares - initially square the mean then take the mean of them and then root the value
33
What are the steps to derive the kinetic theory equation ?
- change in momentum: Particle with mass m with initial velocity u hits the surface and rebounces( elastic collision ) Final momentum - initial momentum = mu - (-mu ) = 2mu - Time taken = 2l / u - Rate of change of momentum = change in momentum over time ( mu^2 / l ) can be equated to the force - force over area = pressure mu^2 / l^3 (gives us the volume ) - taking multiple speeds of the particles into account : P= m (u1… squared ) / v In replace of u1… we sub in (ū ^2 *N ) - taking all directions up and down and sides : We assume velocity is the same in all directions so ć^2 = 3 ū^2 Therefore aP = 1/3 * Nmć^2 / v -
34
Steps to derive the the kinetic theory equation :
m is the mass of one particle N is the number of particles - change in momentum ( 2mu ) - time taken ( 2l / u ) - rate of change of momentum ( mu^2/ L ) - equate the rate of change of momentum to the force - divide the force by the area to get the pressure ( mu^2 / l^3 ) - when you look at multiple particles inn the x directions at multiple speeds ( mNū^2 / v - you then look at multiple directions producing you sū^2 ( 1/3 nmć^2 = PV ) - replace the mean square with crms PV = 1/3 Nm ( crms) ^2
35
Define the internal energy of a gas :
- internal energy of a gas is the sum of the randomly distributed kinetic energy and potential energy of all particles in the gas
36
What is the internal energy of an ideal gas ?
It is just the kinetic energy as ideal gases do not have potential energy due to negligible forces of attraction
37
What is thermal equilibrium?
When two or more bodies are at the same temperature and there is no net flow of energy between the two bodies
38
Describe thermal equilibrium in terms of the molecules
Energy is exchanged between particles through collisions , until average kinetic energy of the particles are the same
39
Why do molecules have potential energy ?
Due to their intermolecular bonds - the further the particles are the greater potential they have ( weaker bonds )
40
How can you change the internal energy of an object ?
- heating - doing work
41
How does applying heat on an object change the internal energy ?
Applying heat energy would increase the internal energy by increasing the kinetic energy of the molecules or state ( giving more potential energy as the particles break from their bonds )
42
How does doing work on the object change the internal energy ?
Change the volume of the object - changing the potential energy
43
What is specific heat capacity ?
The amount of energy required to change the temperature of 1 kg of a substance by 1•c
44
Equation for the SHC ?
C = Q / m*🔺θ
45
What are problems with finding the specific heat capacity experimentally using an immersion heater ?
- if material is not properly insulated , energy would be lost to the surroundings - so will give us higher results for the specific heat capacity
46
What is the specific latent heat of a material ?
The amount of energy required to change the state of 1 kg of a substance without changing the temperature- at the melting or boiling point
47
What is fusion ?
Solid to liquid

Aqa Physics (17 decks)

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