Thermal Physics

Thermal Physics

1. Solids, Liquids and Gasses

   • Energy change = mass x specific heat capacity x change in temperature
     • Specific Heat Capacity - Energy needed to raise 1 kg of a substance by 1K
   • Solids - Fixed positions, strong attraction between molecules
   • Liquid - constantly moving, attraction between molecules
   • Gas - constant random motion, no attraction
   • Specific Latent Heat of fusion of vaporisation is the thermal energy required to change the state of 1kg of a substance
     • Energy change = SLH x mass

2. Ideal Gasses

   • Boyle's Law: pV=constant
   • Charles' Law: V/T=constant
   • Pressure Law: p/T = constant
   • - Large number of molecules in rapid random motion - Collision between molecules are elastic - Gravitational force is negligible - no intermolecular forces except during collisions - total volumes of molecules is negligible compared to the volume of the container -
   • pV=nRT n-number of moles, R-molar gas constant
     • R = 8.31 J mol^-1 K^-1
   • pV=NkT N-number of molecules, k-Boltzmann's constant
     • k = R/Avagadro's constant = 1.38x10 JK^-1
       • Avagadro's constant = 6.02x10^23 mol^1
     • For one molecule of gas

3. Pressure of Ideal Gasses

   • Pressure is the combined force of all the molecules colliding with the walls of the container at any given time
     • The force a particle exerts in proportion to it's change of momentum (2 x mass x velocity) when it rebound of a wall
   • c bar squared is the square of the mean speed of a particle
   • Real gasses are closest to ideal gasses when the pressure is low but the temperature is high

4. Internal Energy andTemperature

   • Change of state is a change in Internal energy, but not temperature because molecules gain potential energy, not kinetic
   • Thermal energy is always transferred from higher temperature regions to lower ones
   • The higher the temperature - both the average and maximum speeds increase, and the speed distribution in the gas also increases
   • When particles collide, sometimes they can either gain or lose speed (and energy), this doesn't alter the total energy in the system
   • Internal Energy is the sum of the kinetic and potential energy of particles in the system
   • E=(3/2)kT
     • Average kinetic energy is proportional to Boltzmann's constant x absolute temperature

5. K = C + 273

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