Rate of Reaction

• Rate of Reaction: Change in concentration of reactant or product per unit time
• Collision Theory: The particles collide with each other and the energy is transferred to the particles
• Activation Energy: The minimum amount of energy required for a reaction to occur
• Right orientation is needed for collision theory
• Rate Distribution

  A) peak

  B) mean

  C) activation energy

  D) maxwell boltzmann distribution

  
• Maxwell Boltzmann Distribution: A graph showing how many molecules have different energies at room temperature.
• Most molecules are inbetween the peak and mean of a Maxwell-Boltzmann distribution
• Increased concentration increases the rate of reaction as the particles are closer together and have more kinetic energy
• Increases pressure increases the rate of reaction as the particles are closer together and have more kinetic energy
• The catalyst lowers the activation energy required for the reaction to occur
• An increase in surface area will increase the rate of reaction because there is more space for reactants to collide with the solid, increasing the number of successful collisions
• Temperature affects the rate of reaction by changing the average speed of the particles which changes the frequency of successful collisions between them
• A closed system is where no reactants or products are allowed to leave or enter the reaction
• Le Chatelier's Principle: If the conditions of a reaction are kept constant, a change in the conditions will result in a change in the position of equilibrium
• When a change is made to a system at equilibrium, the position of equilibrium moves to counteract the change that was made
• When the pressure is increased, the equilibrium position moves to the side with the fewest molecules
• When the concentration of reactants is increased, more products are made as the position shifts away
• If the concentration of products are removed, the position moves to the right
• If the reaction is exothermic in one direction, it is endothermic in the other one
• If the temp increases, the equilibrium favours the endothermic one (right)
• If the temp decreases, the equilibrium favours the exothermic one (left)
• Dynamic Equilibrium: When products can react together to product the original reactants
• Ammonia Haber Process: N2 (g) + 3H2 (g) <--> 2NH3 (g)

  dH = -92 kJ/mol
• Haber Process Equilibrium Changes:

  • Increase Pressure - Shifts to the right
  • Decrease Temperature - Shifts to the right
  • Increase Concentration - Shifts to the right
  • Iron Catalyst - Speeds up the rate
• Haber Process Conditions:

  • 200 atm
  • 450 degrees celsius
• A lower temperature is a higher yield as forward reaction is exothermic and a higher temp is a faster rate.

  450 is the compromise between the yield and rate
• Higher pressures produce a higher yield of the product, but it is more expensive to produce

  200 atm (20000 kPa) is the compromise between the yield and rate
• The Haber Process uses an iron catalyst to increase the rate of reaction. This catalyst is replaced every 5 years
• Producing Ethanol:

  C6H12O6 (aq) --> 2 C2H5OH (aq) + CO2

  C2H5OH -> C2H4 + H2O

  • Production by Hydration
  • Reaction is Reversible
  • Speeded up by an acid catalyst
  • Exothermic = dH -46 kJ/mol
• Positions in Ethanol reaction:

  • Increase pressure
  • Decrease temperature
  • Increase concentration
• General conditions for ethanol reaction:

  • 65 atm
  • 300 degrees
  • Conditions convert about 5% at a time
  • unreacted ethene is removed from the mix
• The equilibrium constant (Kc) is the ratio of concentration of products over reactants after the equilibrium is reached
• If the equilibrium is aA + bB <--> cC + dD:

  Then Kc = ([C] [D])/([A] [B])
• Work these out

  A) -0.8

  B) -0.8

  C) +0.8

  D) 1.2

  E) 2.2

  
• Work these out

  A) -0.4

  B) -1.2

  C) +0.4

  D) 1.2

  E) 0.8

  F) 0.8

  G) 0.4

  
• Kc is only affected by temperature
• Collision Theory:

  • Reacting particles collide
  • Sufficient Energy
  • Correct Orientation
• The slowest step in a reaction is called the rate determining step
• Arrhenias Equation: k = Ae - (Ea/RT)