C5 kinetics

• chemical reactions occur when particles collide with each other
• for a reaction to take place, the colliding particles must have at least the activation energy
• activation energy is the minimum energy needed for a reaction to take place, represented by $E_a$
• factors that affect the rate of a chemical reaction include:

  temperature, concentration, pressure, surface area, catalysts
• temperature affects rate of reaction as increased temperature increases the speed at which particles vibrate, this increases their kinetic energy and frequency of successful collisions
• concentration affects rate of reaction as increased concentration increases the frequency of successful collisions as more particles are present in the same volume, but as the reaction proceeds this plateaus as reactants are used up
• pressure affects rate of reaction as with gases, increased pressure increases the frequency of successful collisions as more particles are present in the same volume, but as the reaction proceeds this plateaus as reactants are used up
• surface area affects rate of reaction as with solids, increased surface area increases the frequency of successful collisions as more particles are available to collide
• catalysts affect rate of reaction without being changed or used up
• in a substance, not all particles have equal amounts of energy, this can be shown using a maxwell-boltzmann distribution
• in a m-b distribution, no particles can ever have zero energy
• in an m-b distribution, most particles have intermediate energy, so the most probable energy is the peak of the curve
• in an m-b distribution, a few particles have very high energy, so the curve never touches zero
• in an m-b distribution, average energy is not the same as most probable, it is slightly to the right
• in an m-b distribution, the area under the curve represents total number of particles
• if you increase the temperature of a reaction, the maxwell-boltzmann distribution shifts to the right and downwards, but has the same area
• if you decrease the temperature of a reaction, the maxwell-boltzmann distribution shifts to the left and upwards, but has the same area
• catalysts are substances which alter the rate of chemical reactions without being chemically changed themselves
• catalysts are typically used in industry as they are expensive but cheaper than increasing temperature and pressure as they are not used up
• catalysts work by providing an alternative reaction pathway which has a lower activation energy
• catalytic converters in engines reduce the levels of pollutants released into the environment
• in a catalytic converter, the catalysts, usually platinum or rhodium, are coated onto a hexagonal mesh
• the catalyst in a catalytic converter works by:

  • absorption = gases form weak bonds with metal catalyst atoms, holding them in the right position, gases react on the surface
  • desorption = products break free from metal catalyst atoms, freeing up room for more gases