A2 - Thermal Flashcards
What two things can cause change in internal energy?
work done, energy transfer
What is the equation for internal energy?
Q=ΔU+W
Work done by system: W is +ve, otherwise -ve
What would happen to the internal energy if the piston of a gas cylinder was compressed
Increase
What would happen to the internal energy if heat was transferred to the surroundings
Decrease
What would happen to the internal energy if the gas pushes the cylinder outwards?
Decrease
What would happen to the internal energy if the gas gains heat energy from surroundings?
Increase
How does a gas thermometer work?
It measures the pressure of fixed vol of gas at given temperature
Define specific heat capacity
energy required to raise the temperature of 1 kg of substance by one degree
What is the equation for the SHC of a metal being heated by electric heater?
P=IV => IVt=energy(Q)
c=IVt/mT
What is the formula for calculating the energy required to change state?
Q=ml
Define specific latent heat
The energy required, per unit mass, to undergo a state change (evaporation/vaporisation)
State Boyle’s Law
p=k/V where k is a constant
What is the shape of a plot of P/V for an isothermic change
1/x shaped
State Charles’ law. Which formula can it be derived from?
V1/T1=V2/T2
based on constant pressure, rearrange the ideal gas law equation
What gives a gas pressure?
The interactions between a the molecules and the cylinder. The more energy they have, the greater the momentum, therefore the impacts they have with the container have more energy, hence greater pressure
What is the volume of a gas at 0K
no volume, no pressure
What is the pressure law
P1/T1=P2/V2 assuming constant volume
What is the combined law for changing pressure, volume and temperature? What does this assume
(P1V1)/T1=(P2V2)/T2
Constant mass of gas
What is crms
An average taken by squaring all the speeds, dividing by the total number of molecules, then rooting. It gives less significance to extremes, creating a more accurate average
What is the shape of the plot of #mpol w/ speed v and v
Boltzmann distribution. Increasing the temperature increases the average speed, but reduces the height of the peak as the molecules have a greater range of speeds
Why might molecules escape from a planet’s surface even if the mean kinetic energy is insufficient?
There may be molecules that exceed escape velocity
What is the internal energy of an ideal gas equal to?
The total energy of the molecules = 3/2 Nkt
Define internal energy of an object
The sum of the random distribution of kinetic and potential energy of its molecules.
In the equation Q=ΔU+W - if work is done by the system, what is W?
Positive.
W is negative when work is done on the system.
In the equation Q=ΔU+W - if heat is transferred from the system, what is Q?
Q0 for heat transferred into system.
What are some ideal gas assumptions?
Molecules are rigid spheres
All collisions are elastic (no ke loss)
No intermolecular forces between gas molecules
Vol of molecules is negligible relative to volume of the container
Collisions are of negligible duration
Molecules are identical
Molecules behave according to the laws of Newtonian mechanics
Good fucking luck :)
Explain the kinetic theory equation, pV=1/3Nm(crms)^2
N=molecules
m=mass of ONE molecule
crms=root mean square speed
1/3 because theoretically 1/3 are moving in each direction (front-back/top-bottom/side-side)
What is Boyle’s law’s relation to kinetic theory equation?
Pressure of gas increases when volume decreases because the molecules travel less distance between impacts so impacts with the walls are more frequent.
Pressure law relation to kinetic theory equation?
Pressure increases as temperature rises because molecules have a higher average speed so impacts with the walls are harder + more frequent.
