chapter 2 Flashcards
(65 cards)
1
Q
define
macroscopic
A
anything seen by the naked eye
density, pressure, volume, temperature
2
Q
define
microscopic
A
things not seen with the naked eye
mass or velocity of a molecule
3
Q
state five
properties of solids
A
- molecules vibrate rapidly about fixed positions
- very strong intermolecular forces
- short and fixed intermolecular spaces
- fixed shape, volume and not compressible
- molecules are vibrating/jiggling in a fixed position
4
Q
state five
properties of liquids
A
- molecules move amongst each other
- strong intermolecular forces
- short and unfixed intermolecular spaces
- has a fixed volume but no fixed shape and it is not compressible
- molecules vibrate but they can slide past one another, and they can move positions
5
Q
state five
properties of gases
A
- the molecules are a great distance apart and it occu[ies all space available
- very weak intermoleculer forces
- very large intermolecular distances
- does not have a fixed shape or volume and it is compressible
- moldcules can move randomly at high speeds past one another (freely moving)
6
Q
define
brownian motion
A
where molecules of air collide with dust particles causing random motion
7
Q
what is seen when
observing brownian motion
A
specks of light against a dark background moving randomly
8
Q
why it occurs
random motion
A
smoke particles are irregulary bombarded by air molecules (that are suspended) from all directions & it is evidence for the kinetic molecular model of matter
9
Q
what is this motion evidence for ?
A
gas molecules are:
1. invisible
2. moving very fast and randomly
3. colliding with smoke particles
4. moving in straight lines
5. changing directions
10
Q
why are the dust particles suspended ?
A
- dust particles are constantly bombarded by energetic, fast-moving molecules from all directions, causing them to move and experience a greater number of collisions on one side than the other
- unequal impacts from air molecules on different sides of a dust particle create a net force, causing random changes in direction, sudden movements, and they remain suspended
11
Q
relate between
diffusion and brownian motion
A
randomly moving particles bounce off each other and move from an area of high concentration to an area of low concentration
12
Q
what are
the uses of thin films
A
- they are used for protection of surfaces from scratches, fingerprints and corrosion (such as optical elements)
- they can also be used in drug delivery, batteries and solar cell construction
13
Q
background
Rayleigh’s oil drop experiment
A
- rayleigh bought a large tub, filled with water, and then put a tiny drop of olive oil on the surface
- he did this again and again until je found the amount of oil that would just cover the whole surface
- he knew the oil molecule consisted of long chains of atoms with one end clinging to the water, so he expected the oil to spread until it did not spread anymore
14
Q
steps
Rayleigh’s oil drop experiment
A
- lightly dust the surface of the water with a fine powder
- measure the diameter of the oil drop using a wire loop, then calculate the radius
- use the wire loop to the place the drop in the surface of the water
- the drop will spread into a roughly circular patch of height ‘h’ and radius ‘R’
- measure the patch’s diameter on the water, then calculate its radius
15
Q
calculatios
Rayleigh’s oil drop experiment
A
- calculate the volume of the oil drop (4/3 x π x (r)^3)
- calculate the volume of the patch (π x (R)^2 x h)
- (4/3 x π x (r)^3) = (π x (R)^2 x h) and make ‘h’ the subject in order to calculate the oil patch’s height
16
Q
assumptions
Rayleigh’s oil drop experiment
A
- the volume of the oil layer is equal to the volume of the oil drop
- oil molecules stand vertically on the water surface
- the thickness of the oil layer is equal to the length of the oil molecule
- the size of an oil molecule must be equal or less than the thickness of the film (h)
the thickness of the film is the upper limit of an oil molecule
17
Q
results of the experiment
Rayleigh’s oil drop experiment
A
- the length of a molecule is estimates using a small drop of oil
- this experiment can be used to give a rough ides of the size of a molecules —> hence an atom
18
Q
notes about the experiment
Rayleigh’s oil drop experiment
A
- the controlled variables were –> the type of olive oil and its purity
- molecules vary constantly in size
- measuring microscope can be used to measure the diameter of the oil drop in the wire loop
- any reading has an inherent uncertainty –> the diameters of the oil drop and the oil film
- the diameter of the oil film is estimated by taking readings at several different places and then calculating the mean diameter
- the estimate uncertainties can be used to estimate the uncertainty in the value of the height of the oil molecule
the unpredictability or randomness that is vital to a system
19
Q
how does a gas exert pressure on its container ?
A
particles move in a continual random motion, and they collide with the walls of the container creating and exerting a force, which gets distrubuted ove the area of the wall
20
Q
state four
factors that increase pressure
A
- increasing the number of molecules (charle’s law)
- increasing the temperature (pressure law)
- reducing the volume of the container (boyle’s law)
- increasing the mas of particles
21
Q
define
temperature
A
the average kinetic energy of molecules
22
Q
what is
absoloute zero
A
it is the theoretical temperature at which the molecules of a substance have the lowest internal energy, and compeltely stop moving
23
Q
define
internal energy
A
the sum of KE and PE of molecules that are moving randomly
24
Q
define
mechanical energy
A
it is the sum of KE and PE of the object
25
# define
ideal gases
it is a gas that obeys charle's, boyle's and the pressure laws
26
# assumptions
ideal gases
1. the motion of the molecules is completely random
2. the forces of attraction between the molecules are negligible
3. molecules have a negligible volume compared to the volume they occupy
4. molecules mkae perfect elastic collisions where no kinetic energy is lost
5. the number of molecules is very large
6. each collision take a negligible time
7. between collisions, each molecule has a steady speed
27
why does an idela gas have zero potential energy ?
because there is no particle-to-particle interaction, which means that internal energy = KE only
28
the internal energy of an ideal gas is directly proportional to ?
1. its mass (number of moles)
2. its temperature
29
# state the rule
pressure law
P1/T1 = P2/T2
30
# explain the kinetic molecular theory of matter according to
pressure law
- when a gas is heated, the molecules move faster
- the higher speed results in a higher frequency of collisions with the container's walls
- the collisions are also harder as the molecules move faster
- together, these cause the pressure to increase
31
# state the rule
charle's law
V1/T1 = V2/T2
32
# explain the kinetic molecular theory of matter according to
charle's law
- when the temperature increases, the speed of molecules increase and they collide harder
- this pushes the piston to move to allow the volume to increase
- however the frequency of collisions decreases due to the increase in volume
- as a result, the pressure remains constant & stops increasing when the pressure inside is equal to the pressure outside
33
# state the rule
boyle's law
P1xV1 = P2xV2
34
# explain the kinetic molecular theory of matter according to
boyle's law
- when a volume of a gas is reduced, molecules of the gas will be more crowded
- which in turn causes them to strike more often with the same speed, so the frequency of collision between the molecules & the walls increases so the pressure also increases
35
# state the rule
the combined gas law
(P1xV1)/T1 = (P2xV2)/T2
## Footnote
if a fixed mass of gas changes from a state to another at diff P, V & T then :
(PxV)/T = constant = nR
36
what are the conditions required for the combined gas law to be valid ?
1. fixed amount of gas
2. the gas must be ideal
37
# state the rules
pV = ?
nRT
NkT
1/3 x m x N x
38
# state the rule
n = ?
m / Mr
39
# state the rule
N = ?
n x Na
40
# state the rule
p = ?
1/3 x ρ x
41
# state the rule
KE = ?
1/2 m v^2 = 3/2 kT
42
# state the rule
v (rms) = ?
√(3RT)/Mr
43
# state
what is earth's escape velocity ?
11 km/s or 11000 m/s
44
when a piston moves **quickly**, why does the temperature increase?
work is done on the gas molecules and they hit the moving piston with more energy
45
when a piston moves **quickly**, why does the pressure increase
- the molecues hit the walls of the container so they create more frequent collisions and harder ones
- which in turn causes a rise in pressure
46
why does adding more gas molecules increase the pressure ?
because the number of collisions between the molecules and the walls of the container increases
47
when air is compressed in a bicycle pump, the temperature increases, why ?
- when air is compressed, its pressure & temperature increase as the volume containing it decreases
- when it is pushed into a smaller space, it is forced to become hotter and more pressurised
- compressing it suddenly makes the molecules move more rapidly, which increases the temperature
| the gas is compressed adiabatically(no heat leaves or enters the system)
## Footnote
work done (V nd P ) --> macro
increase in the avg velocity of particles --> micro
48
# define
heat capacity
the amount of heat needed to raise the temperature of an object by 1℃
49
# define
specific heat capacity
the amount of heat required the raise the temperature of 1 kg of an object by 1℃
50
what is the effect of raising temperature on internal energy ?
increasing the temperature of an object causing molecules to speed up and increase the average kinetic energies of all the molecules in the object, so any rise in the temperature of an object increases its internal energy
51
# state
the advantages and disdvantages for the large specific heat of capacity of water
advantages :
--> it resists the change in temperature, so it can be used in cooling systems
disdvantages :
--> it takes more time for cooking at homes
--> takes more energy
52
# state the rules
Q = ?
m x c x ΔT
P x t
I^2 x R x t
1/2 x m x v^2
any work done
53
# state the rule
C = ?
m x c
54
# state the rules
E = ?
V x I x t
P x t
55
# state the rule
P = ?
(m x c ΔT)/t
56
# state five
conditions that affect the conduction of heat
1. time ( Q ∝ t )
2. difference in temperature (Q ∝ ΔT)
3. cross sectional area (Q ∝ A)
4. thickness (Q ∝ 1/L)
5. material types (co-officient of thermal conductivity)
57
suggest one reason why an experiment to measure the specific heat capacity of an object may not have given the correct value. state if this value is larger or smaller than the true value.
- due to heat loss to the surroundings, the expected change in temperature will be less than the calculated value
- and the specific heat capacity is inversely proportional to the change in temperature, so the calculated value will be greater than the true value
58
# state the rule
Q/t = ?
(kA(T2 -T1)) / X
## Footnote
this equation only holds once a steady state is reached, and the temperature of the conductor does not change
59
# state the rule
q = ?
Q / A
60
what is the reason for heat transfer ?
the temperature difference is the driving force for heat transfer
## Footnote
conduction is the transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles
61
# describe
reaching thermal equilibrium
- heat will flow between two bodies as long as there is a temperature difference between them until thermal equilibrium is reached
- two bodies are said to be at thermal euilibrium if they are at the same temperature (no net exchange of thermal energy between them)
62
# define
thermal conductivity
it is the rate of heat transfer through a unit thickness of a material per unit area per unit temperature difference
63
# state two
what does thermal conductivity depend on ?
1. motion of free electrons
2. molecular vibrations
64
# explain why
when increasing the temperature in metals, the conductivity decreases
- the thermal condcutivity is mainly a function of the motion of free electrons
- as the temperature inceases, the molecular vibrations increase (in turn decreasing the mean free path of molecules), so they obstruct th flow of free electrons
65
# explain why
when increasing the temperature of non-metals, their conductivity increases
there are no free elctrons in non-metals, so only the molecular vibrations are responsible for conduction of heat
