Module 5.1 - Thermal Physics Flashcards
What is an absolute/thermodynamic scale of temperature?
Independent of the properties of any specific substance
Measured in kelvin (K)
What is absolute zero?
The temperature at which a substance has minimum internal energy (lowest limit for temperature - 0K)
Define thermal equilibrium
Objects in contact with each other at the same temperature with no net heat flow between them
What is temperature?
A measure of how hot or cold an object is
What affects the temperature of a material?
The internal kinetic energy (higher KE of particles means higher temperature)
How can an object have a high temperature but not store/transfer a lot of thermal energy?
The particles may have a lot of energy each so there is a high temperature, but if the mass is lower/there are less particles the total energy will be lower so it has less thermal energy
How is thermal energy transferred?
From regions of higher temperature to lower temperature
Points about solids
Particles close together Vibrate around individual fixed position Held together by strong interatomic forces High density Definite fixed (lattice) shape
Points about liquids
Particles can’t move much Slide past each other Mean separation of particles is greater than in solids Weaker interatomic forces than solids Lower density than solids No fixed shape - can flow and be poured
Points about gases
Particles free to move around quickly and in random directions
High mean separation of particles
Very weak interatomic forces
Much lower density than solids and liquids
Easily compressed
Formula for density
Mass of one molecule x number of molecules per cubic metre
Define internal energy
The sum of all the randomly distributed kinetic and potential energies of all the particles (atoms, molecules, ions) in the system
What is the kinetic energy of a system due to?
Movement of particles within the system
Greater mass and velocity of particles means greater kinetic energy
Where is the potential energy of a system stored?
In bonds and intermolecular forces between particles
What happens to the kinetic energy component of the internal energy during a change of state?
No change as there is no change in temperature
What happens to the potential energy component of the internal energy during a change of state?
Will change as intermolecular forces are overcome
Define specific heat capacity
The amount of energy required to raise the temperature of 1kg of a substance by 1°C
Define specific latent heat
The amount of energy required to change the state of 1kg of a substance
Observations and conclusions of Brownian Motion
Can see smoke particles but not air - air molecules must be very small
Lots of changes in direction - lots of air molecules (collisions)
Rapid changes in direction - must have high momentum, small mass so probably large velocity
No pattern in motion - random motion
Features of an ideal gas
Contains a large number of particles
Particles move rapidly and randomly
All collisions are perfectly elastic
Attractive forces between particles during collisions are negligible
Time for collision to happen is negligible compared to time in between collisions
Compared to the volume of gas in the container, the particle volume is negligible
How is gas pressure created?
By collisions of gas particles with the walls of the container
Which feature of an ideal gas is least likely to be true?
Attractive forces between particles during collisions are negligible
Why is it called the Kinetic Theory?
There is no potential energy, as all internal energy is kinetic
Why is the usual pressure equation (P = F/A) not useful for gases?
Gases are in a volume, not across an area
What is Boyle’s Law?
The volume of a fixed volume of gas is inversely proportional to the pressure exerted on the gas, under conditions of constant temperature
pV = constant under conditions of constant temperature
p1V1 = p2V2
Why should you wait in between readings in the Boyle’s Law experiment?
Internal energy of a gas changes as it gains heat energy or if work is done on it
If a gas is going to stay at the same temperature, its internal energy must not change
This means the gas must lose heat when work is done on it during compression if it is to stay at a constant temperature
What is the the Pressure Law?
Pressure is directly proportional to temperature for a constant volume
P/T = constant
P1/T1 = P2/T2
Problems with the pressure law apparatus
Actually measuring pressure in connecting tubes, not the flask
Need a perfect seal at either end of the tube
Air cools as it leaves the flask
Application of the pressure law
Because P changes linearly with T, the apparatus can be used as a thermometer
Called a constant volume gas thermometer and is used to define our temperature scales
Too big and slow for everyday use, so is used to calibrate other types of thermometers
