9.3 - Catalysts

• heterogenous catalyst

  catalyst in a different phase from the reactants

  usually solid when reactants are gases (in industry)
• how does a heterogenous catalyst work?

  reactant molecules bond with solid catalyst (adsorption) so bonds between reactant atoms are weakened and break up forming radicals

  radicals react together and make new molecules that then detach from the catalyst (desorption)
• how do you increase the rate of reaction in a heterogenous catalysis?

  increase surface area of catalyst so increases number of particles that can react at the same time
• homogenous catalyst

  catalysts in the same physical state as the reactants

  aqueous catalyst for reaction between two aqueous solutions
• how do homogenous catalysts work?

  reactants combine with the catalyst forming an intermediate species that reacts to form the products and reform the catalyst
• catalysts on the Maxwell-Boltzmann distribution curve

  line for activation energy is shifted to the left

  because catalysts lower the activation energy so more particles have enough energy to react when they collide
• economic benefits of catalysts

  allow reactions to happen at lower temperatures so it happens at a fast rate while keeping costs down - e.g.: iron used as a catalyst in ammonia production

  give more product in a shorter time

  change properties of a product to make it more useful - e.g.: poly(ethene) made with a catalyst is less dense and rigid but poly(ethene) made with a Ziegler-Natta catalyst is more dense and rigid and has a higher melting point