9 Thermodynamics Flashcards
Heat
Energy transfer from a body or region of high temperature to one of lower temperature
Internal energy
Sum of kinetic energy of the molecules within a body and the potential energy of the bonds between the molecules
Specific heat capacity
The energy transfer needed to change the temperature of 1kg of a substance by 1K
Equation linking energy, mass, specific heat capacity and change in temperature
E = m x c x change in temp (theta)
Equation linking power, mass, specific heat capacity, temperature, time and charge (learn)
P = mc x change in temp/time + charge/ time
How can steady state conditions be kept
A thermistor can be used as part of a potential divider circuit. When the temp decreases, the resistance in the thermistor increases and so more voltage passes through the potential divider and turns the switch on. When the temp increases the opposite occurs.
Specific latent heat of fusion
The energy needed to convert 1kg of a solid to liquid without change in temp
Specific latent heat of vaporisation
The energy needed to convert 1kg of a liquid to a gas without change in temperature
Equation for specific latent heat
L = E/m
Boyle’s law (learn)
P1 x V1 = P2 x V2
at constant temperature
Charles’s law (learn)
V1/t1 = V2/t2
At constant pressure
The pressure law (learn)
P1/t1 = P2/t2
At constant volume
What are ideal gases?
Gases that obey boyles law at all temps and pressures so will never liquefy. This means the internal energy is entirely kinetic as there is no potential energy between bonds in gases
Equation of state (learn)
pV = nRT
P= pressure V= volume n=moles of a gas R= universal molar gas constant 8.31 T= temperature
Equation linking pressure, volume, temperature, number of molecules in gas
pV = NkT
p= pressure V= volume N= no of molecules in gas k= Boltzmann constant 1.38 x 10^-23 T= temperature
Kinetic theory of an ideal gas
The temperature of the gas is related to the speed of the particles and the pressure exerted on the walls
Assumptions of kinetic theory
- no inter particle forces except during collisions
- the time spent during collisions is negligible compared with the time in free motion
- collisions are perfectly elastic
- collisions obey Newton’s laws of motion
- volume occupied by the particles is neglibe
Equation linking pressure, volume, number of particles, mass and velocity
pV = 1/3 x N x m x v^2
3/2 x kT= 1/2 x m x v^2
P= pressure V= volume N= number of particles in a gas m=mass v= velocity k= Boltzmann constant T= temperature
Which equation shows that when temp is zero kinetic energy is zero in an ideal gas
1/2mv^2= 3/2kT
m= mass
v= velocity
k=Boltzmann constant
T= temperature
What is a black body
Black body absorbs all wavelengths of radiation falling on it at all temperatures. They are also perfect emitters of radiation
What is an example of a black body?
A star
Stefan- Boltzmann law
L= ó x A x T^4
L= luminosity Ó= 5.67 x 10^-8 A= area T= temperature
Wein’s law
Lamda max x T= 2.9 x10^-3
Lamda max= peak wavelength
What happens to peak wavelength as temperature increases?
The peak wavelength shifts to larger wavelengths as temperature increases
What is internal energy?
The sum of the random kinetic energies and kinetic energies
What happens to internal energy, KE and PE of an object as it is heated?
KE increases because 3/2 kT and T is increasing
PE stays the same because no bonds are broken
Internal energy increases because KE increases
What happens to internal energy, KE and PE when an object changes state?
KE stays the same because KE= 3/2kT and T stays the same
PE increases because bonds are broken
Internal energy increases because PE increases
In the equation E=mcT what is T
Change in temperature of an object
What happens to a star as it cools
It contracts
What is most of the energy radiated away from earth in the form of?
Infrared radiation
