Thermal Physics Flashcards
How do you work out the internal energy of a body?
Find the sum of the kinetic energies and potential energies of all its particles
How are the kinetic energies and potential energies distributed in a body?
Randomly
How can you increase the internal energy of a body
- Have work done to it to transfer energy to the system
- Increase the temperature of the system
What happens to the internal energy of a substance when it changes states
The internal energy changes:
Only the potential energy changes whilst the kinetic energy remains the same
Why does only the potential energy changes when a substance is changing state
This is because energy inputted is used to break or make bonds between molecules rather than increase the temperature of a substance (from increasing kinetic energy)
Definition of SHC and LH
SHC - energy required to increase the temperature of 1kg of a substance by 1 degree without changing the state of matter
LH - energy required to change the state of matter of 1kg of a substance without increasing the temperature
What are the 3 gas laws
Boyles law = pV = k (when temperature is constant)
Charles law = V/T = k (when pressure is constant)
Pressure law = P/T = k (when volume is constant)
How do you calculate Kelvin
K = C + 273
What is absolute zero?
At 0 Kelvin, it is the temperature that particles have zero kinetic energy and the volume and pressure of a gas are zero
State the ideal gas equation
pV = nRT
n = number of moles
R = molar gas constant
What is 1 mole of substance equal to
1 mole of substance = 6.02*10^23 molecules/atoms
n = N/Na
N = number of molecules
Na = Avogadros constant
n = number of moles
What is Molar mass?
It is the mass of one mole of a substance and can be found by finding the relative molecular mass
What does the area in a pressure-volume graph indicate
Work done
What causes a higher frequency of collisions in a system
- increased temperatures
- increased pressured
- decrease in volume
What are the assumptions of the kinetic theory model?
- No intermolecular force
- Negligible Volume
- Duration of collisions is negligible
- Motion of particles is random
- Perfectly elastic collisions
- Motion of particles follows Newtons law
-Particles move in a straight line
What is an ideal gas
A gas that follows the gas laws perfectly, ideal gas has no potential energy so all of its internal energy is equal to the sum of its kinetic energies
Explain why molecules of a gas exert a force on the walls of its container, refer to newtons laws of motion
There is a change in momentum on molecules because the direction has changed (F = ma)
Newton’s third law, when particle hits the wall it changes direction continue to extent force on the wall.
Explain in terms of the kinetic theory model why pressure drops as volume increase
As volume increases
time between collision increases
speed remain constant due to temperature
- rate of change of momentum decreases
