Thermal Physics definitions Flashcards
Absolute zero
the lowest possible temperature the temperature at which an object has minimum internal energy. The volume and pressure of an ideal gas would be zero at a temperature of absolute zero.
Absolute temperature T
in kelvin = temperature in °C + 273(.15).
Avogadro constant NA
the number of atoms in 12 g of carbon-12. Its value is 6.02 x 1023 mol -1.
Boiling point
the temperature at which a pure liquid at atmospheric pressure boils.
Boyle’s law:
for a fixed mass of gas at constant temperature, its pressure is inversely proportional to its volume.
Brownian motion
the random and unpredictable motion of a particle such as a smoke particle caused by molecules of the surrounding substance colliding at random with the particle. Its discovery provided evidence for the existence of atoms.
Charles’ law
for a fixed mass of an ideal gas at constant pressure, its volume is directly proportional to its absolute temperature.
Energy
the capacity to do work.
Heat Q
energy transfer due to a difference in temperature.
Ideal gas
a gas under conditions such that it obeys Boyle’s law (and the ideal gas law pV = nRT). The interactions between the particles are negligible apart from during collisions, so they have no potential energy.
Internal energy
of an object is the sum of the random distribution of the kinetic and potential energies of its molecules.
Kinetic energy
the energy of a moving object due to its motion.
Mean square speed
the mean value of the square of the molecular speeds of the molecules of a gas.
Kinetic theory assumptions
- Duration of collisions are negligible compared to the time between collisions; 2. The molecules move with random motion; 3. There are no interactions (forces) between the molecules except during collisions); 4. The volume of the molecules is negligible compared to the volume of the gas; 5. All collisions are elastic
Melting point
the temperature at which a pure substance melts.
Mole
one mole of a substance consisting of identical particles is the quantity of a substance that contains NA (6.02 x 1023 mol -1) particles of the substance.
Molar mass
the mass of one mole of a substance.
Pressure
the force per unit area that is exerted normally on a surface
Pressure law
for a fixed mass of an ideal gas at constant volume, its pressure is directly proportional to its absolute temperature.
Root mean square speed, crms:
square root of the mean value of the square of the molecular speeds of the molecules of a gas.
Specific heat capacity c
the energy needed raise the temperature of 1 kg of the substance by 1 K without change of state.
Specific latent heat of fusion
the energy needed to change the state of unit mass of a solid to a liquid without change of temperature
Specific latent heat of vaporisation
the energy needed to change the state of unit mass of a liquid to a vapour without change of temperature
Sublimation
the change of state when a solid changes to a vapour directly.
Temperature
Temperature is proporional to the average translational kinetic energy of molecules in a substance. For an ideal gas they are related by: = 3/2 kT
Thermal energy
the internal energy of an object due to temperature.
Thermal equilibrium
when no overall heat transfer occurs between objects that are at the same temperature as each other. The mean kinetic energy of molecules in the objects will be the same.
