5.1: Thermal Physics, F Flashcards
Define: Absolute zero
The temperature in which a substance has minimal internal energy
What is the kinetic theory
The idea that solids, liquids and gases are made up of tiny moving/vibrating particles
Give an example of how brownian motion can be observed in a lab
Place smoke within a brightly illuminated glass jar, then observe particles using a microscope
Define: Brownian motion
Random movement of small visible particles suspended in a fluid due to collisions with much smaller randomly moving molecules
Define: Internal energy
Sum of randomly distributed kinetic and potential energies of all atoms or molecules within a system
Explain what and why an absolute scale of temperature was created
It is independent of the properties of any specific substance, measured in Kelvins(K)
What is thermal equilibrium
Thermal energy is always transferred from regions of higher to lower regions of temperature, until there is no net flow between them
Define: Specific heat capacity
Spc of a substance is the amount of energy required to raise the temperature of 1kg of the substance by 1K
Define: Latent heat of vaporisation
Amount of energy required to change the phase of 1kg of a substance from a liquid to a gas
Define: Latent heat of fusion
Amount of energy required to change the phase of 1kg of a substance from a solid to a liquid
State Boyle’s law
At a constant temperature, the pressure(p) and the volume(V) of a fixed mass of gas are inversely proportional
-pV = constant
State Charle’s law
At constant pressure, the volume(V) of a gas is directly proportional to it absolute temperature(T)
-V/T = constant
State the pressure-temperature law
At constant volume, the pressure(p) of a gas is directly proportionals to its absolute temperature(T)
-P/T = constant
Given an equation you can use to find the number of particles in a substance
-N = n Na N = no. of particles n = no. of moles Na = Avogadros constant
What is the boltzmann constant(k)
Gas constant for one particle of gas, k = R/Na
R = Gas constant for 1mol of gas
How are Newton’s law used in the explanation of the pressure of an ideal gas
1st - No forces of attraction ∴ inertia until collision
3rd - Collision with wall, exerts equal n opposite force
2nd - Opposite force is equal to rate of change of momentum
∴ change in momentum = 2mu as mu - -mu
What happens to the pressure(p) of an ideal gas, if you increase the volume(V)
The frequency of collisions decreases bc particles have to travel further in between collisions ∴ decreasing the pressure
What happens to the pressure(p) of an ideal gas, if you increase the number of particles(N)
Frequency of collisions increases between the particles and the container ∴ increases total force exerted by all collisions meaning pressure increases
What happens to the pressure(p) of an ideal gas, if you increase the mass(m) of the particles
Following newton’s second law, Force is proportional to mass ∴ heavier particles will exert a greater force meaning pressure increases
What happens to the pressure(p) of an ideal gas, if you increase the speed(c) of the particles
The faster the particles are moving when they collide with the walls, the greater the change in momentum and force exerted ∴ pressure increases
List any 3 of the 6 assumptions involved when trying to model the behaviour of ideal gases
- Gas contains a large number of particles
- Particles move randomly and rapidly
- Volume of particles is negligible, compared to the volume of the gas
- All collisions are perfectly elastic(Ek is conserved)
- Duration of collisions is negligible compared to the time between collisions
- Negligible attractive forces between particles except during collisions
List another 3 different assumptions involved when trying to model the behaviour of ideal gases
- Gas contains a large number of particles
- Particles move randomly and rapidly
- Volume of particles is negligible, compared to the volume of the gas
- All collisions are perfectly elastic(Ek is conserved)
- Duration of collisions is negligible compared to the time between collisions
- Negligible attractive forces between particles except during collisions
What is mean square speed and what are its units
Its the average of the squared speeds of all the particles (m^2/s^2) ∴ square root gives the typical speed(r.m.s.speed)
Show how you can derive an equation for average kinetic energy of particles in an ideal gas
-We know pV=NkT and pressure of ideal gas given by kinetic theory is pV=1/3NmC^2
- ∴ NkT=1/3NmC^2
- cancel N and rearrange
- 3kT = mC^2, we know 1/2mC^2 is Ek of an individual particle ∴
- E = 1/2mC^2 = 3/2kT ∴
-Average kinetic energy, E of one gas particle is given by
E = 3/2kT
What happens to the average kinetic energy of a particle if the temperature of a gas doubles
As Ek and internal energy is directly proportional to absolute temperature. The avg Ek will also double.
