Reaction rates and equilibria

• What is a rate of reaction?


  how fast a reactant was being used up or how fast a product was formed this is usually measured by a change in something/time
• What are the factors that alter the rate of reaction?

  Concentration, pressure, temperature, use of a catalyst and surface area
• What is collision theory?

  It is the theory that two reacting particles must collide for a reaction to occur, they must collide with both enough energy to overcome the activation energy, they also have to be the correct oreintation
• What are the methods of following the progress of the reaction?

  monitoring the removal or the formation. (either the decrease in reactant or increase in product) you can also measure the volume of gas produced in an acid base neutrilisation
• What is a catalyst?

  A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process.
• What is a homogenous catalysts?

  Has the same physical state as the reactants, it reacts with reactants to form an intermediate
• What are heterogeneous catalysts?

  A catalyst that has a different physical state than the reactants, reactant molecules are absorbed onto the surface of the catalyst where the reaction takes place, after reaction the products molecules leave the catalyst surface this is called desorption
• What are the x and y axis of the Maxwell-Boltzmann distribution?

  X is the energy, y is the number of molecules with a given energy
• What are some features of a Maxwell-Boltzmann distribution?

  No molecules have 0 energy

  The area under the curve is equal to the number of molecules

  There is no maximum energy of a molecule, it doesn't meet the x axis at high energy
• What happens to a maxwell boltzmann graph at a higher temperature?


  It's peak isn't as high and is shifted right , but it is more stretched meaning a greater proportion of molecules can overcome the activation energy.
• What is a reversible reaction?


  It is a reaction that occurs both forwards and backwards, many of these are important processes such as industrial processes
• What is dynamic equilibrium?

  It is where the rate of the forward reaction is equal to the rate of the backwards reaction, it occurs in a closed system and the concentrations of the reactants and products remain unchanged
• What is a closed system?

  It is a system isolated from surroundings, so the temp, conc, pressure are unaffected by the outside influences
• What is le chatelier's principle?

  It states that when the system in equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of that change
• How does the concentration affect the changes on equilibrium?

  If you increase the concentration of the reactants more product will form and if you decrease the concentration of the reactants more reactants will form
• What is an example of dynamic equilibrium changes (concentration)?

  Chromate and dichromate ions, chromate ions are formed on the backwards and dichromate on the forwards (yellow to orange), for example when you add H+ ions from an acid the equilibrium will shift to right to counteract the change
• If the forward reaction is exothermic what will increase the yield of the products?

  Low temperature/endothermic conditions
• If the forward reaction is endothermic what will increase the yield of the products?

  Increased temperature, but it will also increase rate which is ideal for an industrial procces
• How does pressure effect equilibria?

  When you increase pressure, it will increase the yield of the side that has the least gas products, however there is a compromise between having a lower yield but a higher rate usually
• How does a catalyst effect equalibria?


  It doesn't effect equilibrium, it just speeds up the rate of reaction
• What is the haber proccess?


  It is the industrial process that forms ammonia from nitrogen and hydrogen, the conditions are usually 450 degrees, iron catalysts and a pressure of 200 atm
• Why are the conditions of the Haber process a compromise?

  It is because the consideration between rate and yield has to take place, even tho yield is decreased by a temp of 450 degrees the rate is increased massively.
• What is Kc?

  It is the equilibrium constant
• How can Kc be calculated?

  Concentration Of products/Concentration of the reactants
• How can Kc be generally considered in a formula? A+B ⇌ C+D


  [C][D]/[A][B]
• What do the brackets represent in the Kc formula?

  Concentrations of
• If the reaction has large numbers infront of the reactants or products how does it effect the Kc formula?


  The large numbers will be put to the power
• What does a Kc value of 1 represent?

  Equilibrium is halfway between the reactants and products
• What does a Kc value greater than 1 represent?

  The position of equilibrium is towards the products
• What does a Kc value that is less than 1 indicate?

  Equilibrium is towards the reactants
• How do you set up a Kc calculation?

  MICE table (Moles) (Initial conc) (Change in conc) (Equilibrium)