chapter 10

• a rate of reaction measures how fast a reactant is used up or how fast a product is formed
• rate of reaction is calculated by doing the change in concentration of reactant or product divided by the given time
• the rate of reaction is fastest at the start of the reaction, as each reactant is at its highest concentration
• the rate of reaction slows down as the reaction proceeds, because the reactants are being used up and their concentrations decrease
• once one of the reactants has been completely used up, the concentrations stops changing and the rate of reaction is zero
• factors that affect rate of reaction

  • concentration( or pressure if reactants are gas)
  • temperature
  • catalyst
  • surface area of solid reactants
• collision theory states that two reacting particles must collide for a reaction to occur
• an effective collsion has:

  • correct orientation
  • sufficient energy
• when concentration increases, rate of reaction increases as the number of particles in a given volume is increased, so they are closer, so they collide more frequently, so their will be more effective collisions in a given time
• increasing pressure of a gas increases concentration, so there will be more in a given volume, which are closer, so collide more often, more successful collisions means a faster rate of reaction
• the progress of a chemical reaction can be measured by:

  • monitoring removal of reactant
  • following the formation of products
• a catalyst increases rate of reaction by providing an alternative reaction pathway of lower activation energy. at the end, the catalyst is regenerated
• a homogeneous catalyst is the same state as the reactant. it forms an intermmediate, which breaks down to form products
• a heterogeneous catalyst is a different state to the reactants. it absorbs reactant molecules onto the surface, reacts, then desorbs the product molecules
• the haber process uses an iron catalyst. hydrogenation of alkenes uses a nickel catalyst
• catalysts can reduce temp needed, which lowers energy and electricity costs, increasing profitability
• industries want to focus on sustainability by doing processes that have high atom economies and fewer pollutants
• the Boltzmann distribution shows the spread of molecular energies in gases.
• in the Boltzmann distribution:

  • the curve starts at the origin to show that no molecules have zero energy
  • the area under the curve is the total number of molecules
  • there is no maximum energy for a molecule, so the x axis would go on forever
• as temperature increases on the Boltzmann distribution, the curve become shorter and shifts the right, and the number of particles that can react is larger
• on the Boltzmann distribution, a catalyst shifts the activation energy to the left, increasing the number of particles that can react
• in dynamic equilibrium:

  • the rate of the forward reaction is equal to the rate of the backward reaction
  • the concentrations of the reactants and products don't change
• le chateliers principle states that when a system in equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of that change
• when the temperature increases, the endothermic reaction is favoured, and when the temperature decreases, the exothermic reaction is favoured
• when pressure is increases the side with least gaseous molecules will be favoured, but when pressure decreases the side with most gaseous moles is favoured
• a catalyst does not affect the position of equilibrium
• the equilibrium law:

  $K^c=$$[C]^c .[D]^d / [A]^a . [B]^b$
• in the equilibrium law:

  • square brackets mean the concentration
  • the small letters are the number of balancing moles
• a kc value of:

  • 1= equilibrium
  • 1+=products favoured
  • -1= reactants favoured