Thermal Physics Flashcards
(107 cards)
1
Q
What’s Avogadro’s number
A
6.02x10^23
2
Q
Define molar mass
A
Mass of one mole of a substance
3
Q
Define molecule mass
A
Mass of one molecule in a substance
4
Q
How to work out kelvin
A
Subtract 273 from the temperature in Celsius
5
Q
What’s is Boyle’s law
A
Pressure of gas’s in inversely proportional to volume
P1/p2 = v2/v1
6
Q
What’s Charles’ law
A
Volume of gas id directly proportional to temperature
When pressure is constant
V1/T1 = V2/T2
7
Q
What’s the pressure law
A
Pressure of gas is directly proportional to temperature
P1/T1 = P2/T2
8
Q
What’s the equation that summarises the tree gas laws
A
pV/T =constant
V1p1/T1 = V2p2/T2
9
Q
What’s the molar gas constant
A
8.31 jk-1 mol-1
10
Q
What’s the Boltzmann equation
A
An alternative for the ideal gas equation
Vp= NkT
11
Q
What’s is Boltzmann constant
A
K= 1.38 x10^-23
12
Q
Define pressure
A
Force per unit surface area which the force acts on
P= F/A
13
Q
What are the five ideal gas law assumptions
A
- The volume of gas is negligible compared to the volume of occupied gas
- The force attraction between the molecule are negligible. The molecules only influence each o their during collisions
- The time between collisions with the containers wall and the other molecules are much greater than the duration of a collision
- The collision between molecules within the wall of the container contain elastic
- There are a large number of molecules whose motion is random
14
Q
Explain Boyle’s law
A
- Has a fixed temperature so momentum change, of each molecule is the same
- More collisions per second so total momentum change is bigger
- So larger force exerted on container wall
- So large pressure exerted
15
Q
Explain Charles law
A
- Average kinetic energy of molecule increases
- So change in momentum of each collision is greater
- To keep the total force and pressure constant the volume increases
- Increasing the time between collisions
16
Q
Explain pressure law
A
- Average kinetic energy of molecule increases
- So change in momentum of each collision in greater
- Volume is constant so the talas force increases
- Increasing pressure exerted
17
Q
What are the main two ways in which energy can transfer from one place to another?
A
- When work is done on an object
- If one object is hotter than another and conduction, convection or radiation occur
18
Q
What are the two types of energy that molecules in a hot substance will have?
A
Kinetic and potential
19
Q
What is internal energy?
A
The sum of the randomly distributed kinetic and potential energies of the particles in a body
20
Q
What is the symbol for internal energy?
A
U
21
Q
What is internal energy measured in?
A
J
22
Q
What is the first law of thermodynamics?
A
The change of internal energy of the object is equal to the total energy transfer due to work done and heating
23
Q
What is the first law of thermodynamics linked to?
A
Conservation of energy
24
Q
What is a useful outcome of the first law of thermodynamics?
A
If work is being done on an object and it is not increasing its internal energy, then it must have an output rate identical to the work being done on it
25
What happens when a sample is heated?
heat energy supplied increases internal energy
* Ek increases, so mean molecular speed increases
* also mean separation slightly increased so small increase in molecular Ep
26
What happens when a samples changes state?
temperature remains constant
* so mean Ek is constant
27
When a sample is changing state, what is the energy being used for?
To break bonds as the sample melts or boils
28
What does heat flow result from?
Temperature difference
29
What happens if two objects at different temperatures are placed in thermal contact?
Heat flows from the higher to the lower temperature until the temperatures equalise
30
When will two bodies be in thermal equilibrium?
When two objects at different temperatures are placed in thermal contact and heat flows from the higher to the lower temperature until the temperatures equalise
31
What happens to internal energy when a substance is hotter?
It is increased
32
What does a temperature scale require?
Two fixed points with fixed degrees between them
33
What is steam point?
The temperature of pure steam at standard atmospheric pressure
34
What is the lowest possible temperature on the absolute scale?
0K
35
What is definition of the triple point of water?
The temperature at which water can exist in all three states
36
How do you convert from Kelvin to Celsius?
Add 273.15
37
What happens when you cool a gas within a fixed volume?
Its pressure drops
38
If you plot a graph of pressure against temperature, with different gases, where will the lines intercept?
At absolute 0, on the negative x-axis
39
What unit does the absolute scale use?
Kelvin
40
What does the rise in temperature for a substance being heated depend on?
* mass of substance
* how much energy is put in
* what the substance is
41
What is the equation for the energy required to heat a substance?
E = mcΔθ
42
What is m in E = mcΔθ?
Mass (kg)
43
What is c in E = mcΔθ?
Specific heat capacity (Jkg⁻¹K⁻¹)
44
What is Δθ in E = mcΔθ?
Temperature change (°C or K)
45
What is the specific heat capacity of a substance?
The energy needed to raise the temperature of unit mass of the substance by 1K without change of state
46
What is the symbol for specific heat capacity?
c
47
How can adding an exact amount of energy to a system be achieved?
By doing work on the system
48
What experiment can be carried out to find the specific heat capacity of a metal?
block of metal of known mass in insulated container
* heater and thermometer inserted
* temperature rise measured
* energy supplied = heat current x pd x time
* c = IVt / mΔT
49
To find the specific heat capacity of a liquid instead of a metal, what changes must be made?
Liquid placed inside container instead and stirred
50
What equipment is used to find the specific heat capacity of a liquid?
Calorimeter
51
What must be included in the calculations to find the specific heat capacity of a liquid? Why is this?
The specific heat capacity of the calorimeter, as it absorbs energy
52
What does the rate of change of temperature in boilers and showers create?v
A rate of energy input, which is power
53
What is the equation that is useful in continuous flow heating?
IV = P = mcΔT / t
54
What are the units of c?
J kg⁻¹ K⁻¹
55
What does the rate of energy flow to sustain the heating in a system calculate?
The power in Watts
56
Properties of solids?
maintain shape
* constant volume
* cannot be easily compressed
* molecules/atoms close together and vibrate in fixed positions
57
Properties of liquids?
* flow and take shape of vessel
* constant volume
* cannot be easily compressed
* molecules/atoms are close together and can move around each other
58
Properties of gases?
* flow and take any shape, fill any space
* take the volume of any vessel or space
* can be easily compressed
* molecules/atoms are far apart and are free to move
59
What will be proportional to the energy supplied when a pure substance is heated?
temp
60
Does a material change state at a constant temperature?
yes
61
Why is the energy transferred to a substance to melt/boil it not obvious or 'hidden'?
Temperature does not change during the change of state
62
What is the energy needed to make a change of state occur?
Latent heat
63
What is latent heat?
The energy needed to make a change of state occur
64
What is the latent heat of fusion?
The energy needed to melt a substance
65
What is the latent heat of vaporisation?
The energy needed to evaporate a substance
66
What is specific latent heat?
How much energy is needed to make a unit mass of a pure substance change state
67
Q
What are the units for specific latent heat?
J kg⁻¹
68
On a temperature-time graph, what does the gradient represent?
The rate of change of temperature
69
On a temperature-time graph, what will a steeper gradient show?
That state heats more quickly - and has a lower specific heat capacity
70
On a temperature-time graph, what is the length of time to change state proportional to?
The specific latent heat for each state change
71
What is the equation for specific latent heat?
E = ml
72
What does E stand for in E = ml?
Energy (J)
73
Q
What does l stand for in E = ml?
Specific latent heat (Jkg⁻¹)
74
Q
What is the pressure of a gas?
The force per unit area that is exerts at right angles to surface
75
What is pressure affected by?
temperature
* volume
* mass of gas particles
76
What are the units of pressure?
pascals (Pa or Nm⁻²)
77
Q
What type of collisions do gas molecules have with the walls of the container?
Elastic
78
Why do gas molecules move at the same speed after they have collided with the container wall?
The collisions are elastic
79
What is the magnitude of pressure proportional to?
The rate of collisions with the container wall
80
How can the pressure of a gas be increased?
increasing temperature - particles move faster
* reducing volume of container - increases chance of particles colliding with wall
* adding more gas - increasing the number of particles
81
What is Boyle's law in words?
The pressure of a fixed mass of gas at constant temperature is inversely proportional to its volume
boils have volume and are hot (volume + temp)
82
What is Boyle's law in equations?
p ∝ 1/V
pV = constant
83
What is an isothermal change?
An experiment done at constant temperature
84
Q
For a Boyle's law experiment at constant temperature, what shape will a pressure-volume graph be?
Downwards curve
85
How could a pressure-volume graph for a Boyle's law experiment be made into a straight line?
Plot p against 1/V
86
What is Charles' law?
Reducing the temperature of a gas but maintaining the same pressure causes the volume to decrease
87
In Charles' law, what does volume increase in proportion to?
Absolute temperature
88
What is the equation for Charles' law?
V = constant T
89
In a Charles' law experiment, what condition must there be for the x-intercept to be at absolute zero?
The gas must be ideal
90
What must happen if a volume of gas is compressed but the pressure is maintained?
Heat must be transferred
91
What happens when you reduce the temperature of a gas at a fixed volume?
Pressure is reduced
92
What equation relates to the pressure law?
p = constant times T
93
What are the three relationships between volume, pressure and temperature?
* Boyle's law
* Charles' law
* The pressure law
94
What is an ideal gas?
One which obeys the gas law exactly
95
When can real gas behaviour be classed as ideal?
When gases are considered at low pressures and higher temperatures
96
What can the gas laws be combined to give?
PV/T = constant
or
P₁V₁ / T₁ = P₂V₂ / T₂
97
Q
What must be true of a gas to be ideal?
* particles themselves can be thought of as taking up no volume
* no significant forces between particles
* motion of particles is random
98
Q
What is Brownian motion?
The random movement of particles in a fluid
99
What is responsible for diffusion?
Brownian motion
100
Why must the same volume of two gases at the same temperature contain the same number of particles?
Because the particles in an ideal gas take up no volume themselves
101
What is the word definition of the Avogadro constant?
The number of carbon atoms in 12g of carbon-12
102
Why did the definition of Avogadro's constant change from using hydrogen to carbon?
It is difficult to get a pure enough sample of Hydrogen-1 without isotopes being present
103
What is the value of the Avogadro constant?
6.023 x 10²³
104
How many
particles does one mole of a pure substance contain?
Avogadro's number
105
What is the molarity of a sample?
How many moles in contains - unit is mol
106
What is the molar mass of a sample?
The mass of 1 mol in kgmol⁻¹
107
Equation for number of molecules in a specific mass?
Ms = NA x Ms / Molar mass
