Chapter 14- Matter: Hot or Cold

A summary of A2 Advancing Physics chapter 14

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  • Created by: R_Hall
  • Created on: 13-04-14 16:57

Activation Energy

  • The average thermal energy per particle is roughly kT, where k is Boltzmann's constant and T is temperature
  • Activation energy is the energy needed to break the bonds that hold particles in matter together. It is the energy needed to make something happen.
  • When kT is big compared to the activation energy, bonds are broken and the matter comes apart.
  • Processes such as a change of state, ionisation in a candle flame, viscous flow, conduction in a semiconductor and thermionic emission require kT to be greater than activ. energy in order to occur
  • Particles gain extra energy through random collisions
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The Boltzmann Factor

  • The Boltzmann factor gives the ratio of the number of particles in energy states E joules apart
  • It varies with temperature. At a low temperature, the factor is very low, so few particles will have sufficient energy to react and the rate of reaction will be low.
  • At high temperatures, the Boltzmann factor approaches 1, so nearly all the particles will have enough energy to react and the reaction will be really fast
  • The rate of a reaction with activation energy E is proportional to the Boltzmann factor
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