Kinetics, Equilibria and Redox

Rates of Reaction
1. Maxwell-Boltzmann
  1. Speed of particles in a gas vary
    1. Shown on distrubution graph
  2. Area under curve is equal to total number of molecules / particles
    1. The peak of curve is the most likely energy of a particle
      1. Average energy is right of the peak
        No particles have zero energy
2. Collision Theory
  1. To react, particles collide
    1. Particles only react when they collide if:
      1. (1) Collide in the correct direction
        (2) Collide with a certain amount of kinetic energy
  2. Activation Energy (Ea)
    1. Minumum kinetic energy needed for reaction to occur
      1. Energy needed to break bonds
3. Factors Effecting Rate
  1. Temperature
    1. Increases number of molecules with have activation energy
      1. Shifts curve to the right with a larger area having activation energy
      2. Also increases the frequency of successful collisions in the reaction
  2. Concentration
    1. Increases frequency of more successful collision, increases rate
  3. Pressure
    1. Does the same as concentration only in gases
  4. Catalysts
    1. Increases rate by providing an alternative route for the reaction that has a lower activation energy
      1. Catalysts are chemically unchanged
    2. Increases the area of curve with correct activation energy without moving the curve itself
4. Measuring Rate
  1. Rate is the change in conc. of product or reactant over time
  2. Timing how long it takes for precipitate to form
    1. Subjective - relies on a persons judgement
  3. Measuring the decrease in mass
    1. Easy and accurate
  4. Measuring the volume of gas given off
    1. Very accurate
Equilibrium Constant
1. Kc is the Equilibrium Constant
  1. 1. Concs of A,B,C,D given in mol/dm^3
      1. Whatever value for a,b,c,d units to the power of these values
2. Calculations
  1. Calculating Equili concs
    1. conc = mole / vol
      1. Use kc to work conc
        Use Kc to work out conc in mixture
        Enter values into the Kc
        Check molar ratio, 1:1 concs equal
        Rearrange Kc equation
3. Temperature changes Kc
  1. Kc only valid for one temperature
    1. If a temperature rise increases product
      1. Kc will rise
        Catalysts don't affect Kc
Redox
1. Oxidation States (OS)
  1. Total number of electrons donated or accepted by a element
    1. Uncombined elements and diatomic have OS of 0
      1. OS of ion or compound ion is the same as its charge
        Sum of OS in a neutral compounds is 0
        Oxygen is nearly always -2
        Hydrogen is nearly always +1
2. Electrons transfered is a redox reaction
  1. OILRIG (of electrons)
    1. Oxidising agent accepts electrons itself is reduced
      1. Reducing agent donates electrons itself is oxidised
3. Half Equations
  1. Combine half equations to form redox equations
    1. Balance equations by CHO and equal electrons
Reversible Reactions
1. Resersible reactions can reach dynamic equilibrium
  1. This is when the reaction is at equilibrium
    1. Where forward and backwards reactions are at the same rate
      1. And the concentrations are equal and constant
  2. Only in closed systems
    1. (nothing added, nothing lost)
2. Le Chatelier's Principle
  1. A reaction at equilibrium will shift to oppose any change
    1. Concentration
      1. E.g. Increase conc. of reactant, shifts to make more product
    2. Pressure
      1. Only involving gases
        Increase pressure, shifts to the side with the least moles
        to reduce pressure
    3. Temperature
      1. Increase temp, shift to endothermic side (+ delta H)
    4. Catalysts
      1. No effect on position of equilibrium, doesnt increase yield either
        Faster to reach equilibrium
    5. Reactions in industry
      1. Balancing high rates with high reaction costs
        High pressure increases rate
        Increasing the pressure too much is expensive to run / maintain
        High temperatures increase rate
        Low temperatures may be needed to oppose exothermic reactions for high yield
        But need a good rate to make product in a good time
        Compromise is required

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Kinetics, Equilibria and Redox

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