Thermal physics Flashcards
Thermal equilibrium
When there is no net flow of thermal energy (objects are same temperature)
Zeroth law
If two objects are in thermal equilibrium with a third, then all three are in thermal equilibrium with each other
Celsius scale
0 = water freezing point
100=water boiling point
Kelvin scale
0 = absolute zero (lowest possible temperature)
change of 1K = change of 1 degree C
T(K) = T(C) +273
Kinetic model - solids
Atoms or molecules are regularly arranged and packed closely together with strong electrostatic forces of attraction holding them in fixed positions. They vibrate in fixed positions and therefore have kinetic energy
Kinetic models - liquids
Atoms or molecules are very close together, but they have more kinetic energy than in solids and can change position and and flow past each other
Kinetic models - gas
Atoms or molecules have more kinetic energy and are much further apart than in a liquid or gas. They are free to move past each other as electrostatic forces are negligible. They move randomly with different speeds
Brownian motion
Random movement of fine grains of pollen floating on water provides evidence for the idea of substances being made of particles - this movement is due to collisions with particles
Internal energy
The sum of the randomly distributed kinetic and potential energy of atoms or molecules within the substance
Potential energy
Due to the electrostatic intermolecular forces between the molecules
Internal energy at absolute zero
kinetic energy =0 so internal energy is just potential energy
EPE in different states
gas - EPE is zero, as electrostatic forces are negligible
liquid- EPE has a negative value (this means energy must be supplied to break the bonds)
solid - large negative value of EPE
Specific heat capacity
The energy required per unit mass to change the temperature by 1K
Methods of determining SHC
Use a heating element in an insulated solid or container of liquid. E=IVt
C=IVt/mΔΘ
Method of mixtures - combine with a substance of known SHC at a different temp and record final temp - calculate C
Constant volume flow heating
c=power/flow rate x ΔΘ
Specific latent heat
Energy required to change the phase per unit mass while at a constant temp
