Thermal physics

• Temperature --> A measure of the average kinetic energy of the particles in a sample of matter, expressed in terms of units or degrees designated on a standard scale
• Absolute temperature scale:

  • Measured in kelvins
  • Converting from degrees Celsius : T(k) = T(oC) + 273
• Absolute zero --> lowest limit for temperature, the temperature at which the particles in a substance have minimal internal energy
• Triple point --> once specific temperature and pressure where a strange thing happens. At this point, the 3 phases of matter of that substance can exist in thermal equilibrium, there is no net transfer of thermal energy between the phases.
• • When 2 objects are in thermal equilibrium there is no net flow of thermal energy between them.
• Thermal equilibrium --> when 2 regions that are in thermal contact no longer transfer heat between them. There is no net transfer of thermla energy between them.
• Solids:

  • Regularly arranged & packed closely together
  • Strong electrostatic forces of attraction between them holding them in fixed positions
  • Can vibrate so have kinetic energy
• Liquids:

  • Atoms or molecules are still very close together
  • Have more kinetic energy than in solids
  • Can change positions & flow past each other
• Gases:

  • Have more kinetic energy than those in liquids
  • Much further apart
  • Free to move past each other as there are negligible electrostatic forces between them
  • They move randomly with different speeds in different direction
• Density:

  • Spacing between the particles in a substance in different phases affect the density of the substance
  • A substance is most dense in its solid phase & least dense in its gaseous phase
  • Water freezes into a regular crystalline pattern held together by strong electrostatic forces between the molecules
  • The molecules are held slightly further apart than in their random arrangement in liquid water, so ice is slightly less dense
• Internal energy --> The sum of the randomly distributed kinetic and potential energies of atoms or molecules within the substance.
• In different phases the atoms or molecules of a substance have different electrostatic potential energies:

  • Gas: the electrostatic potential energy is zero because there are negligible electrical forces between atoms or molecules
  • Liquid: the electrostatic forces between atoms or molecules give the electrostatic potential energy a negative value. The negative simply means that energy must be supplied to break the atomic or molecular bonds
  • Solid: the electrostatic forces between atoms or molecules are very large, so the electrostatic potential energy has a large negative value
• • The electrostatic potential energy is lowest in solids, higher in liquids, and at its highest (0J) in gases
• Specific heat capacity --> the energy required per unit mass to change the temperature by 1K or 1 degree Celsius

  E = mc x delta theta
• Methods of mixture:

  • The methods of mixtures is another way to determine specific heat capacity
  • Known masses of 2 substances at different temperatures are mixed together.
  • Recording their final temperature at thermal equilibrium allows the specific heat capacity of one of the substances to be determined of the specific heat capacity of the other is known
• Specific latent heat --> the amount of energy needed to turn 1kg of liquid onto gas
• Energy = mass x specific latent heat

  E=mL
• • When the substance changes from solid to liquid phase = specific latent heat of fusion
  • When the substance changes from liquid to gas = specific latent heat of vaporisation
• • When a substance is at its melting point it requires energy to change phase from solid to liquid. The energy transferred to the substance increases the internal energy of the substance without increasing its temperature
• Brownian motion --> the haphazard movement of particles in a fluid, as a result of continuous bombardment from molecules of the surrounding medium
• • Particles in both liquids and gases move randomly
  • Particles in fluids are in rapid random motion with a range of speeds
• • If temperature increases, motion increases so visible particles move faster
  • The collisions obey the law of conservation of momentum. The small mass air particles collide with the large mass smoke particles & cause them to move with high speed
  • Basis of the principle of kinetic theory