Activation Energy 42-43 Flashcards
The average thermal energy per particle is given by what?
Thermal energy = KT K is the Boltzmann’s constant, k = 1.38 x 10-23. T is the temperature in kelvin.
What do you do to convert from kT to Jmol-1 ?
Multiply by Avogadros constant (6.02 x 10-23).
What do you do to convert kT to eV ( electron-volts)?
Divide by the charge on the electron ( 1.6 x 10^-19)
Explain some processes involving particles with activation energies.
1) A change of state: the particles need enough energy to break the forces between them.
2) Thermionic emission: if you heat up a conductor, electrons are released from the surface. These electrons need enough enery to escape from the attraction of the positive nuclei.
3) Ionisation in a candle flame: the molecules in the air need enough energy to split up into individual atoms and ions. This is a similar process to thermionic emission.
4) Conduction in a semiconductor: semiconductors will only start to conduct once there are electrons in a high-energy state called the “conduction band” , so electrons need enough energy to jump from the ground state to this higher-energy state.
What is activation energy?
What is the ratio that allows us to see if we can overcome it?
Particle in matter are held together by bonds. The energy needed to break these bonds in a given substance is the activation energy E. ( the Greek “epsilon”).
In the ratio E/kT, when kT is big enough compared with E, the bonds are broken and the matter comes apart.
What happens if the ratio between the activation energy and the average energy of the particles is too high?
Nothing happens.
Explain how is f is the fraction of particles with an extra energy E, what will be the fraction of particles with an energy of 2E?
To get a particle with an average extra energy of about E. So the fraction of particles with an extra energy of 2E will be:
f x f = f2
What are the fraction of particles with the extra energy of 3E and 4E?
3e = f3
4e = f4
