Thermal physics Flashcards
Describe the structure of a solid
The particles are closely packed together in a regular lattice structure
Describe the movement of particles in a solid
They vibrate in a fixed position
Describe the bonding in a solid
There are strong bonds between all of the atoms keeping them held closely together
Describe the structure of a liquid
They are closely packed together but do not have a regular pattern
Describe the movement of particles in a liquid
The particles vibrate and can slide past neighbouring particles allowing more movement
Describe the bonding in a liquid
There are still bonds between the particles but they aren’t as strong as those in a solid
Describe the structure of a gas
The particles are spread out with large gaps between them
Describe the movement of particles in a gas
They move quickly in random directions
Describe the bonding in a gas
There are no bonds between the atoms
What is Brownian motion?
The random zig zag movement of particles travelling in a fluid
How was Brownian motion initially detected?
A microscope was used to observe the movement of pollen grains in water and the pollen grains appeared to move randomly in different directions
Why does Brownian motion occur?
The particles are constantly colliding with particles in the fluid causing them to constantly change direction in a random way
What was the significance of Brownian motion?
It provided eviedence for the existence of atoms
What is temperature?
A measure of the kinetic energy of the particles that make up a body
How does temperature affect the average kinetic energy of a body?
The higher the temperature the higher the average kinetic energy (mean speed)
What does the Maxwell-Boltzman distribution curve show?
The distribution of speeds of particles within a gas
How do you show a lower temperature gas on a Maxwell-Boltzman distribution?
The curve will have a higher peak and will be narrower
How do you show a higher temperature gas on a Maxwell-Boltzman distribution?
The curve will have a lower peak and will be wider
How does heat flow?
From a region of higher temperature to a region of lower temperature
What is thermal equilibrium?
When the temperature of two objects are the same resulting in no net transfer of thermal energy, this means a hotter object will transfer thermal energy to a cooler object until they are the same temperature
What is internal energy?
The sum of the randomly distributed kinetic energies and potential energies of the particles in a body
How can the internal energy of a system be increased?
By transferring energy to it either by heating or by doing work on the system
How is work done on an object?
For a solid a force is applied over a distance (W=Fd), a liquids and gases can be compressed or expanded to change the volume and pressure of the substance meaning the force changes resulting in work being done
What is the phase change between a solid and a liquid called?
Melting or fusion
What is the phase change from liquid to gas called?
Vaporisation or evaporation
What is the phase change from gas to liquid called?
Condensation
What is the phase change from liquid to solid called?
Freezing or solidification
What is the phase change from solid to gas called?
Sublimation
What is the phase change from gas to solid called?
Deposition
Describe the change (if any) in energies as a substance is heated?
The thermal energy is transferred to kinetic energy (hence KE increases) this results in an increase in internal energy, however the potential energy remains the same
Describe the change (if any) in energies during a phase change?
The energy is no longer transferred to kinetic energy (so KE doesn’t change) instead it is used to break or form bonds hence changing the potential energy and therefore internal energy
What are the two ways of defining specific heat capacity?
The energy required to heat 1Kg of a substance by 1°C or it is the energy released when 1Kg of a substance is cooled by 1°C
What assumption is made when calculating specific heat capacity?
The no heat energy is being transferred to the surroundings
What is meant by specific latent heat?
The energy required per Kilogram for the phase (state) transition between solids and liquids or liquids and gases
What are the two ways of defining specific latent heat of fusion?
The energy required when 1Kg of a solid changes to a liquid or the energy released when 1Kg of a liquid changes to a solid
What are the two ways of defining specific latent heat of vaporisation?
The energy required when 1Kg of a liquid changes to a gas or the energy released when 1Kg of a gas changes to a liquid
Why is the specific latent heat of vaporisation a much bigger value than the specific latent heat of fusion for the same material?
During the phase change between a solid and a liquid some bonds need to be broken but during the phase change between a liquid and a gase all of the bonds must be broken, so it requires more energy to break the bonds
What causes gas pressure?
The gas molecules collide with the walls of their container which causes a rate of change of momentum, which is the same thing as saying a force is being exerted on the container, more force acting per unit area means a greater pressure
What is Boyle’s law?
At a constant mass and temperature the pressure and volume of an ideal gas will be inversely proportional to eachother (pV=constant)
How does a graph of pressure against volume vary at higher temperatures?
The curve moves further away from the origin
What is Charles’ law?
At a constant mass and pressure the volume and temperature of an ideal gas are directly proportional to eachother (V/T=constant)
What is the pressure law?
At a constant mass and volume the pressure and temperature of an ideal gas are directly proportional to eachother (P/T=constant)
What is meant by absolute zero?
It is theoretically the lowest temperature possible (occurs at 0K or -273°C) and it is the temperature at which a gas causes no pressure because the particles have zero kinetic energy (so are not moving)
How do you convert from degrees to Kelvin?
Add 273 to your value in degrees
Define one mole
A quantity of identical particles equal to 6.02x10^(23) (Avogadro’s constant)
What is meant by molecular mass?
The mass of one molecule of a substance
What is meant by molar mass?
The mass of one mole of a substance
How do you get from number of moles (n) to number of molecules (N)?
Multiply the number of moles by Avogadro’s constant
What is the difference between pV=nRT and pV=NkT?
pV=nRT is the equation in terms of number of the moles (n) and pV=NkT is the equation in terms of the number of molecules (N)
What is an isothermal change?
A change when temperature is constant
What is an isobaric change?
A change when pressure is constant
Describe the work being done when a gas is compressed
Work is done on the gas by the surroundings
Describe the work being done when a gas is expanded
Work is done by the gas on the surroundings
What are the assumptions of the molecular kinetic theory?
There are a large number of identical point masses in the gas that collide instantaneously and elastically with eachother, they also have no intermolecular forces acting between them, they follow Newton’s laws and travel with random motion
What do the origins of gas laws and molecular kinetic theory differ?
Gas laws are empirical so are based on observations that were then explained mathematically but molecular kinetic theory arose from theory which was then later observed
Derive the equation pV=1/3Nm(Crms)^2
Look in booklet for derivation
How does the internal energy of an ideal gas differ to that of an actual gas?
An ideal gas does not have any potential energy because it is assumed to have no intermolecular forces so its internal energy is equal to its kinetic energy whereas in an actual gas the internal energy is made up of both kinetic and potential energy (because there are intermolecular forces present)
