Kinetics 2                                      07.02.07

HQ Answers

1.      5.0 g   x  [  60s   ]   =  2.0 g/min

               150s        1 min

2.  45.0 g x   1 min/2.35g  =  19.1  min

3.  7.50 min x  3.5 mL / min  = 244 mL

4.  Acceptable :   a, c, e, f

5.  1.34 mol H₂O/min   x  1mol O/ 1mol H₂O =  1.34 mol/min O

Note.   1.34 mol/min O   (   1 mol O₂  )  =  0.670  mol/min O₂

                                          2 mol O

MEASURING REACTION RATE

The following data was obtained for  the reaction:

NaHCO₃ (s)  +   H+ (aq) à  CO₂(g)  +  H₂O (l)  +  Na+ (aq)

_{Sodium Bicarbonate         (Acid)}                                              

The mass of the reactants and products was measured.

The gas was allowed to escape.

Tests:   CO₂ does not support combustion

            Or test for CO₂ with limewater (Ca(OH)₂)

       CO₂ + (Ca(OH)₂)  à   CaCO_{3 (s)}  +  H₂O

         Gas       Clear           white Precipitate (milky)

Calcium hydroxide               Calcium carbonate

Time (s)	Mass (g)
0	150.00
10	149.94
20	149.88
30	149.82

Graph mass vs time

Questions

1. Why is the mass decreasing

2. What is the slope of the line on the graph?

3. What are the units of the…

a. Rise (Y axis)

b. Run (X axis)

c. Slope

4. What units are used for the rate of this reaction?

5. What relationship exists between the slope of the graph and the rate?

Answers:

1. It is an open system…. The CO₂ is lost

6. – (slope) = reaction rate

What factors in a reaction could be measured as the reaction rate?

a.

b. Colour change (intensity of one of the colours of either a reactant getting less or a product getting more)

Change in light intensity/ time

  b.  Temperature change     C/time

  c.  Pressure Change if one gas was produced   kPa/time

  d.  Mass Change     g/time

  H.Q. 7-9

2.1 Factors Affecting the Rate of Reaction

Factor	Examples
1.  Temperature -  generally hot reactions go faster than cold
2.  Concentration – Higher concentrated chemical reactants go faster
3.  Pressure – gases under pressure are more concentrated
4.  Nature of Reactants – the atomic structure of chemicals and their geometry affect the way they react
5.  Catalyst or Inhibitor- a chemical that does not take part in the reaction but speeds it up
6.  Surface Area – increased number of reactant collisions can occur if there is more surface exposed

Note - 

Homogeneous Reactions are those whose reactants are in the same phase except solid + solid (because solids come in different forms of the same phase… powder, chunk, crystal…)

Heterogeneous Reactions…. Reactants in different phases

  Eg.  Solid + liquid,  Solid + aqueous, Liq + gas, two liquids that are not mixing  (immiscible)  like oil and water

Aqueous   à    Gases and Liquids  à   Solids

Fastest     …........ middle  ……….        Slowest

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