SCH 4UI
UNIT 3: ENERGY CHANGES AND RATES OF REACTION
GROUP STUDY REVIEW
1. Calculate the energy released when 10.0 g of steam at 120.0 °C are converted into ice at
minus 20.0 °C.
2. Consider the following reaction mechanisms (i and ii) that could BOTH explain the
reaction:
NO(g) + O3(g)  NO2(g) + O2(g)
i)
NO
 N + O (slow)
ii)
O3
 O2 + O (slow)
N + O3  NO2 + O (fast)
O + NO  NO2
(fast)
O + O  O2
(fast)
(a) Find the overall reaction for both mechanisms.
(b) Give the rate law expression for both mechanisms.
(c) If the actual rate law expression is r = k[NO][O3], is there a mechanism involved?
Explain.
SCH 4UI
UNIT 3: ENERGY CHANGES AND RATES OF REACTION
GROUP STUDY REVIEW
3. Explain, in terms of Collision Theory, why a decrease in temperature should decrease
the rate of a reaction (2 points).
4. The graph below shows a pure substance which is heated by a constant source of heat
supplying 2000.0 joules per minute. Identify the area described in the questions below
and complete the necessary calculations.
UV = 0.36 min, VW = 3.6 min, WX = 3.6 min, XY = 19.4 min, YZ = 0.6 min
a. being warmed as a solid ___________
b. being warmed as a liquid __________
c. being warmed as a gas ____________
d. changing from a solid to a liquid _____
e. changing from a liquid to a gas ______
f. What is its boiling temperature? _________________
g. What is its melting temperature? _________________
h. How many joules were needed to change the liquid to a gas? ____________
i. Where on the curve do the molecules have the highest kinetic energy? ______
j. If the sample weighs 10.0 g, what is its heat of vaporization in J/g? ______
SCH 4UI
UNIT 3: ENERGY CHANGES AND RATES OF REACTION
GROUP STUDY REVIEW
5. Reaction A requires the simultaneous collision of three molecules while Reaction B
requires a collision of two molecules. From a statistical point of view, which reaction
should be faster? Explain.
6. If it takes 41.72 joules to heat a piece of gold weighing 18.69 g from 10.0 °C to 27.0 °C,
what is the specific heat of the gold?
SCH 4UI
UNIT 3: ENERGY CHANGES AND RATES OF REACTION
GROUP STUDY REVIEW
7. The rate of hardening of epoxy glue increases with an increase in the amount of
hardener that is mixed with the glue. What factor affecting reaction rates does this
illustrate? Explain, in terms of Collision Theory, why this factor should increase the rate
of the reaction.
8. A sample of cobalt, A, with a mass of 5.00 g, is initially at 25.0 °C. When this sample
gains 6.70 J of heat, the temperature rises to 27.9 °C. Another sample of cobalt, B, with
a mass of 7.00 g, is initially at 25.0 °C. If sample B gains 5.00 J of heat, what is the final
temperature of sample B. (Hint: think about the specific heat of both samples.)
SCH 4UI
UNIT 3: ENERGY CHANGES AND RATES OF REACTION
GROUP STUDY REVIEW
9. Calculate the enthalpy for the following reaction:
N2(g) + 2O2(g) ---> 2NO2(g) ΔH° = ??? kJ
Using the following two equations:
N2(g) + O2(g) ---> 2NO(g)
ΔH° = +180 kJ
2NO2(g) ---> 2NO(g) + O2(g) ΔH° = +112 kJ
10. If 720.0 g of steam at 400.0 °C absorbs 800.0 kJ of heat energy, what will be its increase
in temperature?
SCH 4UI
UNIT 3: ENERGY CHANGES AND RATES OF REACTION
GROUP STUDY REVIEW
11. The following mechanism has been proposed for the destruction of ozone, O3, by
Chlorofluorocarbons:
CFCl3  CFCl2 + Cl
Cl + O3  ClO + O2
ClO + O  Cl + O2
(a) Write the overall reaction.
(b) Write the rate law expression if the first step is the slow step.
(c) Write the rate law expression if the second step is the slow step (note that
intermediate species are not included in the rate low expression.)
(d) Explain why chlorine atoms are said to catalyze the destruction of ozone.
12. A certain mass of water was heated with 41,840 Joules, raising its temperature from
22.0 °C to 28.5 °C. Find the mass of water.
SCH 4UI
UNIT 3: ENERGY CHANGES AND RATES OF REACTION
GROUP STUDY REVIEW
13. The following data were collected for the reaction: H2 + Br2  2 HBr
[H2]
[Br2]
Rate (molL-1s-1)
2.0 x 10-3
1.0 x 10-3
1.1 x 10-3
–3
-3
4.0 x 10
1.0 x 10
4.4 x 10-3
6.0 x 10–3
1.0 x 10-3
9.9 x 10-3
6.0 x 10-3
2.0 x 10-3
1.98 x10-3
(a) Find and write the rate law expression from the data provided. (Show your work)
(b) Find “k” for the last set of data.
14. When 15.0 g of steam drops in temperature from 275.0 °C to 250.0 °C, how much heat
energy is released?
SCH 4UI
UNIT 3: ENERGY CHANGES AND RATES OF REACTION
GROUP STUDY REVIEW
15. Consider the following reaction: Na2S2O3(aq) + 2 HCl(aq)  2 NaCl(aq) + S(s) + SO2(g)
A precipitate of sulphur, S(s), forms and becomes visible when its concentration exceeds
2.6 x 10-6 molL-1. You would use the formation of this precipitate to “follow” the
reaction.
(a) Find the time required for a precipitate to form if the reaction rate is
1.82 x 10-4 molL-1s-1.
(b) If the experimentally determined rate law expression is:
r = k[Na2S2O3][HCl], find k (including units) when [Na2S2O3] = 3.4 x 10-6 molL-1 and
[HCl] = 2.8 x 10-4 molL-1. Use “r” from part (a).
16. Why does moisture condense on the outside of a glass of cold water?
SCH 4UI
UNIT 3: ENERGY CHANGES AND RATES OF REACTION
GROUP STUDY REVIEW
17. Is it possible for a cup of water to completely evaporate in a room with a constant
temperature?
18. Consider the reaction: KMnO4 + Cl-  MnO4-1 + KCl. The rate of this reaction is
measured by the rate of appearance of coloured MnO4- ion which becomes visible at a
concentration of 1.0 x 10-8 molL-1. The following data were collected:
[KMnO4]
[Cl-]
Time (s)
0.020
0.0010
0.317
0.010
0.0010
1.27
0.020
0.0040
0.790
(a) Find the rate of the reaction for each set of data given above. (Show your work)
(b) Use your rate data to derive the rate law expression for this reaction.
(c) Find the rate of the reaction when [KMno4] is 0.0050 molL-1 and [Cl-] is 1.0 x 10-4
molL-1.
SCH 4UI
UNIT 3: ENERGY CHANGES AND RATES OF REACTION
GROUP STUDY REVIEW
19. How much energy must be absorbed by 20.0 g of water to increase its temperature
from 283.0 °C to 303.0 °C?
20. For a particular reaction, Hrxn = +250 kJ and Eaforward = +375 kJ.
(a) Draw the potential energy curve for this reaction using an appropriate scale for the
axes.
(b) Label: the axes, Ea forward and reverse, Hrxn and the activated complex.
(c) The addition of a catalyst lowers Ea by 100 kJ. Indicate this on your diagram.