Section 6.2 - Thermal Physics Flashcards
What is the internal energy of a gas?
The sum of the kinetic and potential energies of the gas
What is absoloute zero in terms of gas laws?
The pressure/volume can be extrapolated to 0
What is absoloute 0 interms of kinetic energy?
Temperature at which kinetic energy is 0
What is internal energy at absoloute 0.
internal energy is at a minimum.
Kinetic energy is 0.
Lowest ever temperature.
How to increase internal energy?
Do work
heat up
What is SHC
The energy required to heat up 1kg of a substance by 1 degree celcius
What are the 3 gas laws and name them?
P = k/v : boyle’s
P = kt : Pressure law
V = kt : charles’s
What is brownian motion
Random and unpredictable motion
What does brownian motion show?
It shows the exisitance for atoms.
What is a mol?
The amount of a subtance that contains Na number of particles
Mass, molar mass, mol?
molar mass (M) = mass(m) / mol(n)
Number of molecules(N)?
mols * Na
Ideal gas equation
p.v = n.R.T
p.v = NkT
Boltzman constant
K = R/Na
Explain the pressure law
Constant container volume
Heat up gas avergae Ek is higher
Therefore greater velocity, there is a greater rate of change of momentum.
So the force on the container walls is greater
pressure is F/A f goes up A stays the same so pressure goes up as temperature goes up
Charles’s Law
Volume must increase so that the distance molecules must travel is larger between impacts.
keeping the rate of change of momentum pe runit area constant
Boyles law
Volume is less so distnace between impacts is less.
Less time spent between impacts so less time over the same rate of change of momentum means a greater force
how does the boltzmann curve change with temp?
Higher temp = flatter curve
peak shifted to the right higher Crms
Kinetic enrgy derrivation
Single molecule in box with length l.
Mollecule travels distance l with velocity v.
Its change in momentum is 2mv
To find the force we divide it by the time it take to travel 2 lengths
so that become 2mv/2l/v => mv^2/l
presssure is f/a so then divide force by width and height to get mv^2/vol
then for 1 molecule p.v = mv^2
Now for all mollecules in the gas to find mass multiply by big N.
to find average velocity : Chnage v^2 to mean speed in x direction so crms^2 = x^2 +y^2 + z^2
to get mean crms we divide just the x direction by 1/3 to get p.v = Nm * 1/3/Crms^2
Ideal gas assumptions
All collisions are elastic
No inter-mollecular forces act on the particles
Volume of particles are negliible compared to the size of the container
Time for collisons is negligible compared to the time between collisions
Particles are in random motion
Mean kinetic energy
Ek = 3/2.k.t
What energy is changing when a substance changes state?
Internal and potential
Changes of energy when heating a solid
Kinetic energy is the main change of the internal energy, a small potential energy increase is associated with expansion
