Topic 9- Thermodynamics Flashcards
1
Q
specific heat capacity
A
the amount of energy needed to raise the temperature of 1kg of the subtance by 1K
2
Q
specific heat capacity equation
A
Δe = mcΔθ
3
Q
measuing specific heat capacity experiment
A
- insulate the material and place and heater and thermometer inside it (solid or liquid)
- heat the substance for a set amount of time
- measure the change in temperature of the substance.
- using the power of the heating appliance use E = Pt to calculate the energy
- use Δe = mcΔθ to calculate the value value of c
4
Q
units of specfic heat capacity
A
J/kg/K
5
Q
Why is the calculated value of c always too large?
A
energy from the heater did not all go to increase the internal energy. Some will have escaped to increase the internal energy of the room.
6
Q
Specific Latent heat
A
the energy needed to change the state of 1kg of the substance without changing the temperature
7
Q
What is specific latent heat?
A
the energy needed to break the bonds a subtance melts or boil (changes state)
8
Q
Latent heat of fusion
A
solid -> liquid (melting)
9
Q
Latent heat of vapourisation
A
liquid -> gas (boiling)
10
Q
Latent heat equation
A
E = LΔm
11
Q
latent heat unit
A
J/kg
12
Q
measuring latent heat
A
- place a beaker of cold water on a top pan balance with a heater in it
- heat the water for a set time
- measure the change in mass during the heating
- work out the energy inputted from the power of the heating appliance E=pt
- Work out the latent heat using E = LΔm
13
Q
Why doesn’t the temperature change when a substance is changing state?
A
the energy is being used to change the state
14
Q
Internal energy
A
the sum of the kinetic and potential energy within a system
15
Q
Heating
A
the process when energy is transferred from a higher temperature object to a lower temperature object
16
Q
heat
A
the energy transferred by heating
17
Q
1st law of thermodynamics
A
energy in a system is conserved: change in internal energy = heat transfer + work done (U=Q+W)
18
Q
0th law of thermodynamics
A
if two systems are at the same temperature, there is no resultant flow of heat between them, the system is in thermal equilibirum
19
Q
thermal equilibirum
A
two systems are at the same temperature so there is no resultant flow of heat between themWhat
20
Q
What can happen when the internal energy increases?
A
- increase in temperature
- change state
21
Q
What does doubling the number of atoms do?
A
doubles the time to heat up
22
Q
As the temperature of a gas increases:
A
- average particle speed increases
- the maximum particle speed increases
- the distribution curve becomes more spread out
23
Q
how is energy transferred between particles
A
via momentum in collisions
24
Q
kelvin -> celsius
A
θ = T - 273
25
Celsius -> kelvin
T = θ + 273
26
Boyles Law
for a fixed mass of gas at constant temperature pressure, p, is inversely proportional to volume, V.
27
Work done, w =
pressure, p * Change in volume, V
28
Pressure volume graph
1/x curve
29
pressure, 1/v graph
straight line graph through the origin
30
PV =
a constant
31
P1V1 =
P2V2
32
As the Pressure, P, doubles to 2P the volume, V, ....
halves to 1/2V
33
Boyles law experiment
1. slowly use the foot pump to increase the pressure
2. record the volume for different pressure level
3. plot p agaisnt 1/v, if the graph is directly proportional it follows boyles law
34
Charles Law
for a fixed mass of gas at constant pressure the volume, V, is (directly) proportional to the temperature, T (in kelvin)
35
V/T =
a constant
36
V1/T1 =
V2/T2
37
Volume Temperature graph
straight line
- if in kelvin directly proportional
- if in celsius cuts the y axis
38
Charles law experiment
- record the volume and temperature of the cold water
- heat the water and record the temperatures
- plot volume agaisnt temperature. If the graph is straight line and approximately crosses the x-axis at -273 degrees it follows Charles law
39
Gay Lussacs pressure law
far a fixed mass of gas at constant volume pressure is proportional to temperature
40
P/T =
a constant
41
P1/T1 =
P2/T2
42
Gay Lussacs experiment
1. heat is applied to the cylinder
2. measure the temperature and volume at regular intervals
3. plot P agaisnt T if its a straight line graph then it obeys the law
43
How does gay lussacs and charles experiments give evidence for an absolute zero temperature
They should be directly proportional however they are not and both intersect the x axis at -273. This gives evidence for the kelvin temperature scale where 0K is absolute zero.
44
ideal gas
a gas where the molecules do not interact
45
why do real gases no obey the gas laws as well
- if too cold they condense
- if under too much pressure they condense
- molecule interactions result in imperfect result
46
How did they find the exact value of absolute zero
extrapolating the graph from charles law and gaylussacs law
47
absolute zero
the lowest possible temperature where all particles have the minimum possible kinetic energy
48
how are kelvin and celsius linked
they have the same interval
49
ideal gas equation
pV = NkT
50
what is k in the ideal gas equation
boltzman constant
51
pressure in a container of gas
particles move about and collide with the walls of the the container the change in momentum causes a force on the side of the container which results in pressure P = F/A
52
A gas is ideal if:
- molecules have negligible size
- molecules are identical
- collisions are perfectly elastic
- no inter-molecular forces
- enough molecules for statistical analysis
- motion is random
53
derive pV = 1/3Nm
1. when the loecules bounce off the side of the box its momentum changes from +mv to -mv so change in momentum is -2mv
2. the time for the molecule to get back to its original position is 2L/v (v=st)
3. the force on the side of the cube is calculated by: F = Δp/Δt = 2mv/ (2L/v) = mv^2/L
4. P = F/A where A = L^2 so P= mv^2/V
5. if the box contained N molecules the pressure would increase by N times so P = Nmv^2/V
6. since the molecules move in all directions we can assume there is a third of each direction so P = Nmv^2/3V
7. all the molecular speed vary so we used the root mean square P = Nm/3V
54
What does a maxwell-boltzmann distribution look like for lower temperatures
close together higher peak
55
What does a maxwell-boltzmann distribution look like for higher temperatures
spread out lower peak
56
Whats on the axes of a maxwell-boltzmann distribution
Number of molecules against speed
57
What does the peak of a maxwell-boltzmann distribution show?
the most probable speed
58
how to calculate the root mean square
1. square all the values
2. take the mean
3. square root
59
what can 1/2m = 3/2RT be used for
to calculate the mean kinetic energy
60
how to derive 1/2m = 3/2RT
equate pV = NkT and pV = 1/3Nm
61
black body
a body that absorbs and emits all incident radiation of all wavelengths
it is a perfect emitter and a perfect radiator
62
Why is the predicted behaviour of a black body not true
due to the ultraviolet catastrophe
63
stefan boltzmann law
L = σAT^4
64
What does the stefan boltzmann law do?
links the factors of a black body
65
wiens law
λmax T = 0.0029
66
What does wiens law explain
the relationship between peak wavelengths and the temperature of a body
67
in terms of molecular energy changes why does the temperature remain constant when something boils?
The average kinetic energy is constant and any input energy increases the potential energy causing molecules to move further apart
68
What does an intensity against wavelength graph show?
The peak wavelength/ distribution of wavelengths for a black body
69
If there is a higher temperature how does intensity against wavelength graph change?
The peak is higher and shifted to the left (the peaks do not align)
70
Theorectically what should an intensity against wavelength graph look like? Why doesn't it look like this?
exponential decay, its not due to the ultraviolet catastrophe
71
What causes line spectra
After an electron has been exicted it drops back down the energy levels and releases energy in the form of photons which are then detected and put into line spectra.
72
What gives line spectra?
all elements
73
The hotter the object...
the more energy it emits
74
When drawing a blackbody curve:
- The left hand side must be drawn steeper than the right hand side
The energy per second must decrease towards (but not reach) zero as the wavelength increases.
- The line must not cross the energy per second axis (y-axis)
75
Higher temperature for boltzmann vs blackbody curves
boltzmann - shifts right
| blackbody - shifts left
76
axes for a blackbody curve graph
y axis - energy per second per m^2 (intensity)
| x axis - wavelength
77
area under a boltzmann distrubution
number of particles
78
boltzmann distrubution axes
y axis - number of molecules
| x axis - kinetic energy / speed
79
the greater the photon energy (hf)...
the greater then number of energy levels the electron moves up
80
internal energy of a gas
Just kinetic energy (no PE)
| KE = 3/2kT
81
Why does pressure decrease as it cools
- reduced average kinetic energy
- travels slower / less collisions with wall
- change in momentum is less therefore force on walls is less
- therefore pressure is less
82
condition to use PV/T = PV/T
- one variable is constant
- mass constant
- acts as an ideal gas
83
relationship between SHC and Number of atoms
The energy required to raise the temperature of 1kg is proportional to the number of atoms in 1kg.
