Thermal Physics Flashcards
Internal energy of an object
The sum of the random distribution of the kinetic and potential energies of its molecules.
First law of thermodynamics
The change of internal energy of the object = the total energy transfer due to work done and heating.
Solid
The atoms and molecules are held to each other by forces due to the electrical charge of the protons and electrons in the atoms. Molecules vibrate randomly about fixed positions.
Liquid
The moelcules move about at random in contact with each other. The forces between the molecules are not strong enough to hold the molecules in fixed positions.
Gas
The molecules also move about randomly but much further apart on average than in a liquid.
Thermal equilibrium
A state of a system in which all parts are at the same temperature.
Ice point
0 degrees celsius
Steam point
100 degrees celsius
Absolute zero
0 K
Triple point of water
273.16 K
Temperature in celsius
Absolute temperature in kelvins - 273.15
Absolute zero definition
The lowest possible temperature, an object at absolute zero has minimum internal energy.
Specific heat capacity, c, of a substance
The energy needed to raise the temperature of unit mass of the substance by 1 K without change of state.
The unit of specific heat capacity
J kg^-1 K^-1
The energy needed to raise the temperature of a substance of mass, m from T1 to T2
ΔQ = mc (T2 - T1)
Sublimation
The process by which some solids vaporise directly when heated.
The specific latent heat of fusion, l, of a substance
The enegy needed to change the state of unit mass of the substance from solid to liquid without change of temperature.
The specific latent heat of vaporisation of a substance
The energy needed to change the state of unit mass of the substance from liquid to vapour without any change of temperature.
The energy, Q, needed to change the state of mass, m, of a substance from liquid to vapour without change of temperature.
Q = m x l
Pressure of a gas definition
The force per unit area that the gas exerts normally on a surface.
Boyle’s law
pV =constant
Isothermal change
Change at constant temperature.
Isobaric change
Change at constant pressure.
Charle’s law
V/T = constant
Work done by a gas on a piston
p ΔV
The pressure law
p/T = constant
Brownian motion
Term used to describe the motion of individual molecules in a gas.
The Avogrado constant, NA
6.023 x 10^23, the number of atoms in exactly 12g of the carbon isotope 12C6.
Definition of one mole
The quantity of substance that contains NA particles. Unit is the mol.
The molar mass of a substance
The mass of 1 mol of the substance.
An ideal gas
A gas that obeys Boyle’s law, the three experimental gas laws can be combined to give the equation pV/T - constant, for a fixed mass of ideal gas.
Ideal gas equation
pV = nRT
Molar gas constant, R
8.31 J K^-1 mol^-1
Boltzmann constant, k
1.38 x 10^-23 J K^-1
Kinetic theory equation
pV = 1/3 N m (Crms)^2
Assumptions made about molecules in gas
The volume of each molecule is negligible compared with the volume of the gas. Molecules do not attract eachother and move about in continual random motion. Collisions are elastic.
Kinetic energy of gas molecule
1/2 m (Crms)^2 = 3/2 k T = 3RT/2NA
