Chapter 10

• Rate Calculation

  change in concentration/time
• Rate units

  mol/dm3/s
• Collision Theory

  Two reacting particles must collide for a reaction to occur, and must be in the correct orientation and have sufficient energy to overcome the activation energy of the reaction.
• What must particles have in order for a reaction to occur?

  Correct orientation and sufficient energy to overcome the activation energy
• How does increasing concentration affect rate of reaction?

  The number of particles in a given volume increases, so there are more frequent collisions in a given time. Rate increases
• How does decreasing concentration affect rate of reaction?

  The number of particles in a given volume decreases, so there are less frequent collisions in a given time. Rate decreases
• How does increasing pressure affect rate of reaction?

  Same number of particles occupy a smaller space, so collisions are more frequent. Rate increases
• How does decreasing pressure affect rate of reaction?

  Same number of particles occupy a larger space, so collisions are less frequent. Rate decreases
• How does rate change as a reaction proceeds?

  Concentration of reactants decreases, so less frequent collisions. The limiting reagent gets used up and rate falls to 0
• How does increasing temperature affect rate of reaction?

  Particles have more kinetic energy to overcome the activation energy, so collisions are more frequent. More successful collisions in a given time, so rate increases
• What is a catalyst?

  A substance that increases the rate of reaction without being used up in the process
• How do catalysts work?

  They provide an alternative route for a reaction with lower activation energy
• Benefits of catalyst in terms of costs

  Lower temperatures and pressures require less electricity, so energy cost is lowered
• Benefits of catalysts in terms of sustainability

  Reduced fossil fuel consumption, higher atom economy and less toxic waste
• Homogenous Catalyst

  Same physical state as reactants
• Heterogenous Catalyst

  Different physical state as reactants
• What is a reversible reaction?

  A reaction that takes place in both the forwards and reverse directions
• Dynamic equilibrium

  The equilibrium that exists in a closed system when the rate of the forward

  reaction is equal to the rate of the reverse reaction and concentrations do not change
• Closed System

  A system isolated from its surroundings so the temp, pressure and concentration of the reactants and products are unaffected by outside influences
• Reaching dynamic equilibrium

  Rate of forward reaction decreases, and backwards reaction increases, until the rate of the forwards and backwards reactions are the same
• What are the features of a system in dynamic equilibrium?

  Rate of forwards and backwards reactions are the same, all reactants and products are present and there is a constant concentration of reactants and products
• How does increased concentration of reactants affect equilibrium?

  Equilibrium will shift to the right
• How does decreased concentration of reactants affect equilibrium?

  Equilibrium will shift to the left
• How does increased pressure affect equilibrium?

  Equilibrium will shift to the side with the fewest number of moles
• Pressure only applies to

  reactions involving gas
• How does increased temp affect rate of reaction?

  Equilibrium will shift to favour the endothermic reaction
• How does decreased temp affect rate of reaction?

  Equilibrium will shift to favour the exothermic reaction
• Catalysts

  Increase the rate of the forwards and backwards reactions equally, and increase the rate at which equilibrium is established
• Catalysts do not...

  affect the position of equilibrium
• Kc

  Equilibrium constant in terms of concentration
• What does [ ] show?

  The concentration at equilibrium of each substance
• Kc =

  [Products]/[Reactants]
• In Kc expressions, each substance is raised to the power of what?

  The number of moles shown in a chemical equation
• A Kc value of 1 indicates

  Equilibrium is halfway between reactants and products
• A Kc value of less than one indicates

  Equilibrium is towards the reactants (left)
• A Kc value of greater than one indicates

  Equilibrium is towards the products (right)
• The larger the value of Kc

  the further the equilibrium position lies to the right
• What is the rate of a chemical reaction?

  -The rate of a chemical reaction measures how fast a reactant is being used up or how fast a product is being formed.

  
  

  -The rate of a reaction can be defined as the change in concentration of a reactant or a product in a given time.
• What is the equation of the rate of reaction?

  Rate = change in concentration / time
• How does the rate of the reaction change during the reaction?

  -At the start of the reaction the reaction is very fast as the 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 concentration stops changing and the rate of reaction is zero.