Chemistry 12 (HL)
Unit 2 / IB Topic 6.1
Kinetics 1 – Practice Problems
Measuring Rates of Chemical Reactions
1.
Nitrosyl chloride (NOCl) decomposes according to the equation:
2 NOCl(g) à 2 NO(g) + Cl2(g)
The initial concentration of nitrosyl chloride was 0.580 M. After 8.00 min, this concentration
decreased to 0.238 M.
2.
a)
Calculate the rate of decomposition of nitrosyl chloride during this interval. Express
your answer in mol/L•s.
b)
Calculate the rate of production of Cl2.
Write the equation for the complete combustion of ethane (C2H6).
If ethane burns at a rate of 0.20 mol/L•s, what is the rate of production of carbon dioxide? What
is the rate of consumption of oxygen?
3.
The rate of a reaction is found by measuring any distinct property of a reactant or product OVER
TIME.
Examples:
reactions producing gases
change in volume of gas / time
change in total pressure / time
change in total mass / time (only for CO2)
reactions involving a reactant
or product with a colour
change in absorbance / time
- the substance will absorb light of a
complementary colour
reactions involving weak
acids or bases
change in pH / time
reactions involving changes
change in conductivity / time
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Chemistry 12 (HL)
Unit 2 / IB Topic 6.1
ion amounts
chemiluminescent reactions
change in light intensity / time
How might you measure the rates of these reactions experimentally? List as many techniques
as you can.
4.
a)
Cu(s) + 2 AgNO3(aq) à 2 Ag(s) + Cu(NO3)2(aq)
b)
H2O2(g) à H2O(l) + 1/2 O2(g)
c)
CH3Br(aq) + H2O(l) à CH3OH(aq) + H (aq) + Br (aq)
d)
2 MnO4 (aq) + 10 Cl (aq) + 16 H (aq) à 2 Mn (aq) + 5 Cl2(aq) + 8 H2O(l)
e)
NH4NO3(s) à NH4 (aq) + NO3 (aq)
f)
CaCO3(s) + 2 CH3COOH(aq) à Ca(CH3COO)2(aq) + H2O(l) + CO2(g)
g)
Zn(s) + H2SO4(aq) à ZnSO4(aq) + H2(g)
+
–
–
+
+
–
2+
–
Hydrogen peroxide, H2O2(aq), releases oxygen gas, O2(g), as it decomposes according to the
equation:
2H2O2(aq) à 2H2O(l) + O2(g)
3
50.0 cm of hydrogen peroxide solution was placed in a boiling tube, and a drop of liquid detergent
was added to create a layer of bubbles on the top of the hydrogen peroxide solution as oxygen gas
was released. The tube was placed in a water bath at 75 °C and the height of the bubble layer was
measured every thirty seconds. A graph was plotted of the height of the bubble layer against time.
a)
Explain why the curve reaches a maximum.
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Chemistry 12 (HL)
Unit 2 / IB Topic 6.1
b)
Use the graph to calculate the rate of decomposition at 120 s.
c)
Use the graph to calculate the average rate of reaction.
5.
Given the reaction: A + B à 2C + D
The following data were collected over a period of time:
Time (s)
0.00
3.00
6.00
9.00
12.00
15.00
18.00
[A] (mol/L)
3.20
2.42
1.95
1.63
1.40
1.23
1.10
[C] (mol/L)
0.00
1.528
2.50
3.14
3.62
3.94
4.18
a)
Plot a graph of concentration vs. time for both A and C on the same set of axes.
b)
Calculate the average rate of production of C over the 18.00 s of the reaction.
c)
Calculate the average rate of consumption of A in the first 4 seconds.
d)
Calculate the average rate of consumption of A in the last 4 seconds.
e)
What does the difference in the values for c and d suggest?
f)
Calculate the instantaneous rate of production of C at t = 9.00 s.
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Chemistry 12 (HL)
Unit 2 / IB Topic 6.1
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