c6 rates of reaaction

    Cards (29)

    • What is activation energy?
      The minimum amount of energy needed for a reaction to take place
    • The collision theory
      • The more successful frequent collisions there are, the higher the rate of reaction
      • If particles collide within enough energy, they will overcome the activation energy and react
    • What is collision frequency?
      How often particles collide
    • Pressure and conc vs rate of reaction
      • Increasing pressure/ conc increases rate of reaction
      • Because there are more reactant particles in a given space
      • Which means there are more frequent, successful collisions
      • So rate of reaction increases
    • Temperature vs rate of reaction
      • Increasing temp increases rate of reaction
      • Because the particles gain thermal energy which transfers to kinetic energy
      • More energy causes particles to move faster and have more frequent collisions
      • More frequent, successful collisions = faster rate
    • SA vs rate of reaction
      • Increasing SA increases rate of reaction
      • Because breaking up a solid increases its SA:volume ratio
      • So there is more area for reactant particles to collide with
      • More frequent, successful collisions = faster rate
    • Catalyst vs rate of reaction
      • Adding a catalyst increases rate of reaction
      • Because catalysts provide a path with lower activation energy for the reaction
      • So particles can collide with more energy
      • More successful, frequent collisions = faster rate
    • What is rate of reaction?
      How long it takes for reactants to turn into products
    • How can you measure rate of reaction?
      EITHER
      Measure quantity of reactant used up over time
      OR
      Measure quantity of product formed over time
    • What can you measure rate with?
      1. Gas syringe
      2. Mass balance - calculate change in mass
      3. Colour change / precipitation
      4. Measuring cylinder
    • Measuring rate with gas syringe
      • Measure vol of gas produced over time
      • More gas given off = faster reaction
      • + Easy to take regular readings
      • + Easy to plot on graphs
      • -- Reaction can break the syringe - not safe
    • Measuring rate with mass balance
      • Calculate change in mass/time if a gas is produced
      • Mass will decrease as gas is released to the surroundings
      • Add cotton wool to conical flask to prevent chemicals leaving the flask
      • + Easy to plot mass and time on a graph
      • + Most accurate method
      • + Highest resolution
      • -- SAFETY ISSUE of gas being released into the room
    • Measuring rate with a measuring cylinder
      • Measure the volume of gas produced/time
      • More gas produced = faster reaction
      • + Easy to take regular readings
      • + Easy to plot on graph
    • Measuring rate by colour change/precipitation
      • Record the visual change during a reaction
      • ONLY if the reactants are transparent and the product is a precipitate that will cloud the solution (or vice versa)
      • Put conical flash on a black cross, time how long it takes to disappear (if product is a precipitate and reactants are transparent)
      • OR time how long it takes for cross to be visible (if product is transparent and reactant is coloured)
      • -- Results are subjective (people might not agree over when the mark disappears)
      • -- Can't plot a graph
    • Mean rate of reaction = quantity of product formed / time
    • What is mean rate of reaction measured in?
      g/s
      g/cm^3
      mol/s
    • What is time measured in?
      Seconds
    • What are reactants and products measured in?
      Grams
      cm^3
      mol
    • Mean rate of reaction = quantity of reactant used / time
    • Rate of reaction GRAPHS
      • Steeper line = faster rate
      • Over time lines will plateau because reactants are used up
    • Lines 2 + 3 = increased rate of reaction due to increased SA, catalyst or increased temp
      Line 4 = increased rate due to increased conc (results in more reactant particles so more product can be made)
    • Reversible reactions
      • Shown by a double arrow in equations - reaction goes both ways
      • Reactants form products
      • Products form reactants
      • Reaction reaches equilibrium when 1. the rate of backwards and forwards reaction is the same and 2. the conc of product and reactant remains constant
    • What is equilibrium?
      When the rate of both forward and backward reactions are the same
    • When will a reversible reaction reach equilibrium?
      In a closed system
      Must be optimum conditions
    • What is Le Chatelier's Principle?
      If you change the conditions of a reversible reaction at equilibrium, the reaction will shift forwards or backwards to make a new equilibrium
    • Factors affecting Le Chatelier
      • Pressure
      • Temperature
      • Concentration
    • Pressure and Le Chatelier (only in gases)
      • Increased pressure = reaction shifts to the side with fewer molecules
      • Fewer collisions = pressure is decreased
      • Decreased pressure = reaction shifts to the side with more molecules
      • More collisions = brings pressure back up
    • Temperature and Le Chatelier
      • Increased temperature = reaction shifts in the endothermic direction
      • So takes IN heat energy and lowers temp (more products for endothermic)
      • Decreased temp = reaction shifts in exothermic direction
      • So releases heat energy OUT and raises temp (more products for exothermic)
    • Concentration and Le Chatelier
      • Increased conc of reactants = reaction shifts FORWARDS to make more products
      • Decreased conc of products = reaction shifts BACKWARDS to decrease the amount of reactants