Matter Flashcards
(25 cards)
What is Boyle’s law?
Pressure is inversely proportional to volume
Describe how pressure is directly proportional to density of a gas?
Pressure is directly proportional to mass of a gas, so pressure * volume is also directly proportional.
Mass / volume is density, hence pressure is directly proportional to density.
What is Bernoulli’s law?
Pressure is directly proportional to the number of molecules in a given volume
Describe how to obtain the number of moles in a sample
n = Mass of the sample / mass of 1 mole of the sample
Describe how to obtain the number of molecules in a sample?
N = number of moles * NA
What would make an ideal gas?
The forces between molecules are negligible (e.g. Van der Waals force)
What is Charles’s law?
Pressure is directly proportional to temperature at a constant volume
Describe an experiment to find absolute zero in degrees Celsius
- Use a glass capillary tube sealed at one end with a liquid index trapping a length ‘L’ of air
- ‘L’ is directly proportional to Volume ‘V’, and ‘V’ is directly proportional to temperature ‘T’, so we can see how ‘V’ varies with ‘T’
- Plot a graph of ‘V’ against ‘T’, then draw a line of best fit
- Extrapolate the data backwards, and when ‘V’ = 0, ‘T’ = absolute zero, which is roughly -273 degrees Celsius
Use Boyle’s law, Bernoulli’s law and Charle’s law to derive the ideal gas equation
p α 1/V, p α N and p α T.
Therefore, pV = NkT.
Where ‘k’ is the Boltzmann constant
What is the other form of the ideal gas equation and where does it come from?
pV = nRT.
In one mole of gas, N = NA.
As NA * k is a constant, we give it the new letter R, which is the gas constant.
For ‘n’ moles of gas, we multiply RT by n
What are the 3 big rules of an ideal gas?
- The forces between molecules are negligble
- Volume occupied by the molecules is negligble
- All collisions are perfectly elastic
What impulse does a single particle travelling with constant velocity ‘c’ exert upon the wall of a container?
Impulse = change in momentum = mc - (-mc) = 2mc
What is the average force a single particle exerts upon a container?
F = 2mc/Δt = mc2/x
What is the equation for the average force exerted on a container by N particles, and explain why the constant is chosen?
F = 1/3 * Nmc2/x
At any given point, a particle can travel in the x, y or z directio. Therefore, for N particles, we would expect 1/3N to be travelling in the x direction.
Link the equation for average force exerted by a particle to the ideal gas equation. Use a cuboid with length x, width y and height z.
pressure = force / area
F = Nmc2/3x
Area of one side = yz
Pressure = Nmc2/3xyz = Nmc2/3V
pV = 1/3 * Nmc2 = NkT = nRT
Why does the speed of a particle need to be averaged?
It is the biggest contributer the force, as F α c2
How do you find the average kinetic energy of a particle
1/3Nmc2 = 2/3N(1/2mc2)
2/3N(1/2mc2) = NkT
1/2mc2 = 3/2kT
How is the distance of a particle found after N steps
sqrt(N)
How do you find the energy per mol from specfic latent heat?
Emol = SLH * molar mass
Why does water evaporate even at lower temperatures? (e.g. outside on a sunny day)
- Molecules have a range of energies
- Some molecules have enough energy to escape the surface of the material
- This brings the mean energy per molecule down
- The molecules then gain energy through collisions, and a small amount of molecules will gain enough energy through successive collisions to escape the surface
What is the rule of thumb for process occuring at a normal rate?
E/kT is roughly 15kT - 30kT
What happens if a process’s E/kT is more or less than the normal amount?
Greater than 30kT = Slow process
Less than 15kT = Fast process
Explain the boltzmann factor ‘f’
The fraction of particles that have enough energy to begin the next stage of a process. e.g. If a dice was removed from a tray when it landed on 6, then ‘f’ would be 1/6.
Explain why the decrease of a number of particles in a process due to completion of the process is an exponential relationship (i.e. why is N α e-constant)
Nx = fx * N0
f is a ratio = e-E/kT
Hence, Nx = N0 * e-E/kT
