Rates of reaction and energy changes

    Cards (47)

    • what are enzymes ?
      biological catalysts
    • what are enzymes used in the production of ?
      alcoholic drinks
    • what type of reaction is breaking of bonds ?
      endothermic
    • what type of reaction is making of bonds ?
      exothermic
    • whats activation energy ?
      the minimum amount of energy needed by colliding particles in order for a reaction to happen
    • describe an exothermic change/reaction ?
      a change or reaction in which heat energy is given out
    • describe an endothermic change/reaction ?
      a change or reaction in which heat energy is taken in
    • what do exothermic changes do to a solutions temperature ?
      increase if in solution
    • what do endothermic changes do to a solutions temperature ?

      decrease if in solution
    • how do reactions occur ?
      reactions occur when particles collide
    • what increases the rate of reaction ?
      • increased frequency
      • energy of collisions
      • increased temperature
    • reactant particles move more quickly
    • exothermic reaction profile
      =
    • endothermic reaction profile
      =
    • explain an exothermic reaction profile ?
      • energy level of the reactants is greater than the energy level of the products
      • the energy change is negative (transferred to surroundings)
    • explain an exothermic reaction profile ?
      • energy level of the reactants is lower than the energy level of the products
      • the energy change is positive (transferred from surroundings)
    • how does surface area to volume ratio effect the rate of reaction ?
      • the rate of reaction increases when the surface area : volume ratio of a solid reactant increases (lumps made into powder)
      • more particles of reactant are available
      • the frequency of successful collisions increases
    • how does a large piece of material effect the rate of reaction ?
      • smaller surface area
      • slower reaction
    • how does a large piece of material effect the rate of reaction ?
      • larger surface area
      • faster reaction
    • a catalyst provides an alternative reaction pathway that has a lower activation energy than the uncatalysed reaction
    • how does the addition of a catalyst increase the rate of reaction ?
      adding a catalyst increases the frequency of successful collisions because a greater proportion of collisions now exceeds this lower activation energy
    • the overall heat energy change for a reaction is exothermic if ...
      more heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants
    • the overall heat energy change for a reaction is exothermic if ...
      less heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants
    • whats a catalyst ?
      a substance that speeds up the rate of reaction without altering the products of the reaction being itself unchanged chemically and in mass at the end of the reaction
    • how does changes in temperature effect the rate of reaction ?
      the rate of reaction increases when the temperature increases as the particles gain energy
    • reactions increase when temp increases as...
      • the particles move faster
      • the frequency of collisions increases
      • the energy of collisions increases so a greater proportion of collisions are successful
    • how does concentration and pressure effect the rate of reaction ?
      the rate of reaction increases if the concentration of a dissolved reactant increases, or if the pressure of a reacting gas increases
    • reactions increase with an increased concentration as..
      • there are more particles in the same volume
      • the frequency of successful collisions increases
    • whats the heat energy change for a salt dissolving in water ?
      can be exo or endo depending o the salt used
      ( temp can change due to precipitate of salt)
    • whats the heat energy change of neutralisation reactions ?
      can be exo or endo but its usually exothermic
    • whats the heat energy change of displacement reactions ?
      exothermic
    • whats the heat energy change of precipitation reactions ?
      can be exo or endo depending on the substances involved
    • when these reactions take place in solution, temperature changes can be measured to reflect the heat changes
    • what units are the energies of bonds given in ?
      ( KJmol-1)
    • how to calculate the energy change in a reaction given the energies of bonds ?
      • add together the bond energies for all the bonds broken in the reactants ("energy in")
      • add together the bond energies for all the bonds formed in the products ("energy out")
      • energy change = in-out
      • the steeper the line the greater the rate of reactions
      • fast reactions finish sooner
    • whats an acid ?
      a compound that dissolves in water to form a solution with a PH of less than 7
    • whats an alkali ?
      a compound which dissolves in water to form a solution with a PH of more than 7
    • whats bond energy ?
      the energy needed to break one mole of a covalent bond is its bond energy, measured in kilojoules per mole
    • whats collision theory ?
      the reactant particles can only react with eachother when they bump into one another