FORM III TOPIC 7. CHEMICAL KINETICS, EQUILIBRIUM AND ENERGETICS

CHEMISTRY FORM THREE QUESTIONS AND ANSWERS 

FORM III TOPIC 7. CHEMICAL KINETICS, EQUILIBRIUM AND ENERGETICS:

            QUESTIONS:

1. Identify the most correct answer at each item from the alternatives provided.

i) Describes rate and factors that cause chemical reaction and affect rate of chemical reaction.

   A: equilibrium reaction
   B: reversible reaction.
   C: chemical kinetics
   D: equilibrium position

 ii) Lowering of activation energy.

      A: decrease rate of chemical reaction
      B:  make reacting particles to start reaction easily.
      C: favours backward reaction
      D: stops the chemical reactions.

 iii)  According to the Collision theory, chemical reaction only takes place when particles

    A: collide  B: break up  C: bond. Warmed

 iv) Even if reacting particles contact, they will not react if

    A: they do not posses activation energy
    B: they are cold
    C: they are few in number
    D: temperature increases

 v) It favours forward reaction when temperature lowered

    A: reaction of hot chemicals
    B: acid base reaction
    C: endothermic reaction
    D: exothermic reaction

vi) It proceed in both forward and back ward directions.

    A: chemical reactions  B: chemical equilibrium
    C: irreversible reaction  D: reversible reaction

 vii) Change of either temperature, pressure or concentration to the chemical reaction that is at equilibrium may cause

     A: shift of equilibrium position
     B: increase of time for completing the reaction
     C: increase of rate of reaction
     D: high consumption of reactants

 viii) A simple reversible reaction

        A: forward reaction is fast than backward direction
        B: both forward and backward directions proceed at the
             Same rate
         C: change direction with change of conditions
         D: its backward direction is fast than forward direction

  ix) Increase of temperature to the chemical reaction
   
      A: makes reacting particles closer
      B: makes reacting particles disorganised
      C: increase kinetic energy to the reacting particles
      D: increase potential energy to the reacting particles

  x) At a very law temperature the reaction rate slows down even if the reaction is

      A: exothermic  B: endothermic  C: at high temperature  D: reversible

2. Match list A and list B

             List A
       i) The contact process
      ii) The Haber process
     iii) Dissolving concentrated sulphuric acid in water
     iv) Has effect to equilibrium reactions that involves gases
      v) Speed  up rate of chemical reaction
     vi) Irreversible reaction
    vii) Equilibrium point
    viii) increases of temperature
      ix) Rate of chemical reaction
       x) Reversible reaction and equilibrium reaction

                List B

     A: proceed in only one direction
     B: proceed in either direction
     C: take place in the closed systems
     D: water formation
     E: obtained when the rate of forward dire
          ction is equal to that of backward dire
          ction
    F:  favours forward direction in endothermic reaction.
    G: increase production of ammonia gas.
    H: 1/time
    I:  sulphur trioxide production
   J: a  catalyst
   K:  exothermic reaction
   L: pressure.
   M: ammonia gas production

3. Explain the meaning of the following words:-

       a) Chemical catalyst
       b) Reversible reaction
       c) Rate of chemical reaction
       d) Irreversible reaction
       e) Endothermic reaction
       f)  Exothermic reaction
    

4. State Le  Chatelier's principle.

5. a) Mention factors that affect rate of chemical reaction.

     b) Explain how factors mentioned in(5 a) above affect rate of chemical reaction.

6. Distinguish endothermic reaction from exothermic reaction.

7. List down the factors that affect equilibrium position.

8. What will happen to the equilibrium position?

       

Change of energy=-Ve.                                                    

 (a) if temperature is lowered to the system 

    (b) if some ammonia gas removed from the system

(c) if pressure increased

9. Draw energy level profiles for endothermic reaction and exothermic reactions.

10. Form III students performed an experiment to determine rate of reaction from volume of hydrogen gas produced against time when zinc granules reacted with dilute hydrochloric acid and the following results were obtained.

(a)  Draw graph of volume against rate       (b) Calculate the rate of the chemical reaction.

(c) At what time high volume of hydrogen gas collected?

d) At what time did the experiment produced the largest volume of oxygen?

11. State one example for endothermic reaction and one for exothermic reaction.

12. Observe the chemical equation the state the effect of increase of pressure to the equilibrium position since the system is at equilibrium.

13.

             Explain the effects of the conditions to the production of sulphur trioxide gas from reaction of sulphur dioxide and oxygen if the system is at equilibrium.

      (a) increase of temperature
      (b) increase of pressure
       (c) removing some sulphur dioxide.
       (d) adding a catalyst to the system.

14. State conditions that enable us to know if the chemical reaction is taking place.

        ANSWERS:
1.
   i) C       vi) D
  ii) B.     vii) A
 iii) A     viii) B
 iv) A       ix) C
 v)  D        x) A

2. i) I          vi)A
   ii) M      vii) E
  iii) K      viii) F
  iv) L        ix) H
   v) J         x) C

3. a) is a substance which alters the rate of the chemical reaction and remain unchanged at the end of the reaction.

    b) is a chemical reaction that proceed both forward and backward direction depending varying conditions such as temperature,pressure and concentration.

   c) refers to ratio of the amount of substance used or produced to the time taken.

   d) is a reaction that proceed in one direction.

   e) is a reaction that absorbs energy from the surrounding in form of heat.

  f) is reaction which releases energy to the surrounding in form of heat.

4. It states that "if the system is at equilibrium and one of the factors is changed, the equilibrium position shifts to minimise the effect of change and new equilibrium is established".

5. (a) factors which affect rate of chemical reaction are:-
          -temperature
          -concentration
          -surface area
          -catalyst

     (b) Temperature
                 It affects rate of chemical reaction by increasing kinetic enerqy to reacting particles when it is increased to the system.

            If the chemical reaction is endothermic, its rate increase with increase of temperature(vice versa is true)

            If  the chemical reaction is exothermic, its rate increase with decrease of temperature(vice versa is true)

           Concentration.

              It affects the rate of chemical reaction by increasing or lowering reacting particles.

            The rate of the chemical reaction increase with increase of concentration( number of reacting particles). Vice versa is true.

               Surface ares.
                 It affects rate of chemical reaction depending on the size of chemical substances.

          Small size of chemical substance(powdered) makes higher surface area than the relative large size(granules)

          The rate of chemical reaction increases with increase of surface area(vice versa is true)

              Catalyst.
                 It affects the rate of chemical reaction by speeding up the reaction rate.

      Presence of catalyst in the chemical reaction increase rate of chemical reaction.(vice versa is true)

6. -Endothermic reaction absorbs heat energy from  the surrounding WHILE  Exothermic reaction release heat energy to the surrounding.

    -In an endothermic reaction, the products are formed at relative hing temperature WHILE in an exothermic reaction, the products are formed at relative low temperature.

     -Endothermic reaction indicated by positive symbol of its energy change. (change of energy= +Ve)  WHILE Exothermic reaction indicated by negative symbol of its energy change( change of energy= -Ve)

7. Factors that affect equilibrium position are:-
       -Temperature
       -Concentration
       -pressure

     TEMPERATURE

   Effect of temperature if the reaction is endothermic.
                   When temperature increased to the system it favours forward reaction and if the           Was at equilibrium, increase of temperature shifts equilibrium position to the right
           In order to minimise the effect of change in the system.

   Effect of temperature if the reaction is endothermic.
            Lowering of temperature favours forward reaction hence equilibrium position shifts
            or moves to right to minimise the effect of change in the system.

  CONCENTRATION.
         Concentration affects equilibrium position by favouring the side which have high concentration.
         If there is high concentration to the reactant side forward reaction is favoured and equilibrium position shifts to the right. Vice versa is true.

   PRESSURE.
        Effects of pressure to the system depends on total volume or number of moles at each side of the reaction.
         If at the product side(right) consists fewer number of moles , forward reaction is favoured and equilibrium position shifts to the right. Vice versa is true.

8. (a) lowering of temperature increase rate of forward reaction since the chemical reaction is exothermic.
       Equilibrium position shifts forward.

   (b) if some of ammonia gas removed from the system, the rate of backward reaction because at the left side concentration is lowered.
       Equilibrium position shifts backward.

   (c) increase of pressure speed up rate of forward reaction.
         Equilibrium position shifts backward because it is a side that produce fewer molecules.
     NB. Pressure has no effect if both sides of the equilibrium position have equal number of molecules.

9

10. (a)

     (b) rate is calculated from the graph by obtaining the gradient as shown in 10 (a) above.

              Gradient=rate
              If the slope is steep it means the rate of reaction is high.

    (c) at 180 second, high volume of the gas collected.

    (d) in the first 20 seconds  the largest volume of the gas produced because its slope is steep .

  NB.
        The scales of the graph are easily obtained by taking the highest value of the data dividing by the number of the lines that you prefer to use.

          For example the highest value on vertical line is 66.

           But i prefer to use 18 lines of the graph
                       To get scale interval.
                                   66/18=4
          4cm3 is the interval between two lines(one square)

11. - examples of endothermic Reactions are
                 *photosynthesis process
                 *water vapour formation process

       - examples of exothermic reactions are
                  *explosion
                   * reaction of water an concentrated acid.
                   * combustion of fuel.

12. There is no effect to the equilibrium position because both sides of the equilibrium system have equal volume(number of moles).

13. (a) increase of temperature favours backward reaction since the reaction is exothermic. This makes low production of sulphur trioxide.

       (b) increase of pressure favours forward reaction because to the product side there is fewer moles and low volume. This makes high production of sulphur trioxide gas.

       (c) removal of some sulphur dioxide cause backward reaction due to decrease of concentration to the reactants side. This makes low production of sulphur trioxide gas.

       (d) addition if a catalyst to the system does not affect the production of the sulphur trioxide gas because catalyst will speed up both forward reaction and backward reaction.

14. The conditions that enable us to know if the chemical reaction is taking place are.

        -colour change of the mixture
        -smell
        -precipitation
        -temperature change