Ch. 12-13: Kinetics and Equilibrium
AP Review Questions
**Know rate constant units: - (Order – 1) = power on M, power on time is always -1.
Rate = k [A]2[B]1 units of k = M-(3-1)min-1 = M-2 min-1
1) Which of the following must be true for a
reaction that proceeds spontaneously from
initial standard state conditions?
a) ∆Go > 0 and Keq > 1
b) ∆Go > 0 and Keq < 1
c) ∆Go < 0 and Keq > 1
d) ∆Go < 0 and Keq < 1
e) ∆Go = 0 and Keq = 1
2) If ∆Go > 0 for a reaction, which of the
following statements about the equilibrium
constant, K, is true?
a) K = 0 b) K > 1 c) K < 1 d) K = 1 e) K = Go
Questions 3-6
a) VSEPR theory
b) Kinetic molecular theory
c) Transition state theory
d) Quantum theory
e) Atomic Theory
3) Theory used to determine, predict, or explain
molecular geometry.
4) Theory that explains paramagnetism the best.
5) Theory that incorporates the activation energy.
6) Theory used to explain the effect of
temperature on reaction kinetics.
Questions 7-9
a) ideal gas law
b) law of conservation of matter
c) equilibrium law
d) rate law
e) Hess’ law
7) This law describes the order of a reaction.
8) This law can be used to determine molar
masses.
9) This law is fundamental to all stoichiometry
calculations.
12) The kinetic molecular theory is used to explain
a) reaction rates b) bond vibrations
c) gas behavior d) catalysts
e) activated complexes
13) A certain chemical reaction is described by a
first-order rate law. What is the rate constant,
in units of s-1, for the reaction if the half-life is
determined to be 228 min?
a) ln (228 X 60) b) ln2 / [228 X 60]
c) ln 2 d) ln ([At]/[Ao]) e) 228 s-1
10) Which of the following is an integral part of
collision theory?
1. collision frequency 2. collision energy
3. collision orientation
a) only 1 and 2 b) only 1 and 3 c) only 1
d) 1, 2, and 3
e) only 2 and 3
11) A reaction has the following rate law: Rate =
k [A][B]2. The units for the rate constant are
-1
a) s b) mol L-1 s-1 c) L2 mol-2 s-1
d) L mol-1 s-1 e) mol s-1
14) The rate law for a reaction is found to be rate =
k [A]2 [B]. Which of the following is true
about this system?
a) A plot of log rate versus time is a
straight line.
b) The units for the rate constant are mol2
L-2 s-1.
c) This reaction is unlikely since it
implies the simultaneous collision of
two atoms of A and one of B.
d) It is unlikely that the first step of the
mechanism is the rate-limiting step.
e) All third order reactions are
endothermic.
16) All of the following affect reaction rates when
all reactants are in solution EXCEPT
a) nature of reaction substances
b) pressure
c) temperature of reactants
d) concentration of reactants
e) presence of catalyst
15) The addition of a catalyst to a chemical
reaction will bring about a change in which of
the following characteristics of the reaction?
I. the activation energy
II. the enthalpy change
III. the value of the equilibrium constant
a) I only b) II only c) I and II only
d) I and III only e) II and III only
17) The rate constants for the decomposition of
acetaldehyde were measured at five different
temperatures. A plot of ln k versus 1/T was
found to give a straight line. The slope of this
plot is equal to
a) –k b) k c) –Ea / R d) Ea e) A
Questions 18-19
F2(g) + 2 ClO2(g) → 2 FClO2(g)
Experiment [F2] [ClO2] initial rate of
(M) (M)
disappearance
of F2 (M/sec)
1
0.10 0.010 1.2 X 10-3
2
0.20 0.010 2.4 X 10-3
3
0.40 0.020 9.6 X 10-3
18) Based on the data given in the above table,
which of the following expressions is equal to
the rate law for the reaction given above.
a) Rate = k [F2]
b) Rate = k [ClO2]
c) Rate = k [F2] [ClO2]
d) Rate = k [F2]2 [ClO2]
e) Rate = k [F2] [ClO2]2
19) What is the initial rate of disappearance of
ClO2 in experiment 2?
a) 1.2 X 10-3 M/sec
b) 2.4 X 10-3 M/sec
c) 4.8 X 10-3 M/sec
d) 7.0 X 10-3 M/sec
e) 9.6 X 10-3 M/sec
20) Dinitrogen pentoxide decomposes according to
the following balanced equation:
N2O5(g) → 2 NO2(g) + ½ O2(g)
The rate of decomposition was found to be 0.80
mole liter-1 sec-1 at a given concentration and
temperature. What would the rate be for the
formation of oxygen gas under the same
conditions?
a) 0.20 mole liter-1 sec-1
b) 0.40 mole liter-1 sec-1
c) 0.80 mole liter-1 sec-1
d) 1.60 mole liter-1 sec-1
e) 3.20 mole liter-1 sec-1
21) Time(min) [A] M [B] M
0
0.50
6.00
10
0.36
6.00
20
0.25
6.00
30
0.18
6.00
40
0.13
6.00
A reaction occurred in which A reacted with a large
excess of B to form C. The concentrations of the
reactants were measured periodically and recorded in
the chart above. Based on the data in the chart, which
of the following statements is NOT true?
a) The reaction is first order in [A].
b) The reaction is first order overall.
c) The rate of reaction is constant over time.
d) The half-life of reactant A is 20 minutes.
e) The graph of ln [A] will be a straight line.
22) For the reaction:
2 NO(g) + O2(g) → 2 NO2(g)
which two of the following possible intermediate
mechanisms would support this reaction?
1. 2 NO(g) → N2O2(g)
2. NO(g) + O2(g) → NO3(g)
3. 2 NO2(g) → N2O2(g) + O2(g)
4. NO3(g) + NO(g) → 2 NO2(g)
5. NO(g) → NO(g) + O2(g)
a) 1 and 2 b) 2 and 3 c) 3 and 4
d) 2 and 4 e) 1 and 4
Questions 23-26
a) activation energy
c) ionization energy
e) lattice energy
b) free energy
d) kinetic energy
23) The energy required to convert a ground state
atom in the gas phase to a gaseous positive ion.
24) The energy change that occurs in the
conversion of an ionic solid to widely separated
gaseous ions.
25) The energy in a chemical or physical change
that is available to do useful work.
26) The energy required to form the transition state
in a chemical reaction.
27) Which of the following best describes the role
of the spark from the spark plug in an automobile
engine?
a) The spark decreases the energy of
activation for the slow step.
b) The spark increases the concentration
of the volatile reactant.
c) The spark supplies some of the energy
of activation for the combustion
reaction.
d) The spark provides a more favorable
activated complex for the combustion
reaction.
e) The spark provides the heat of
vaporization for the volatile
hydrocarbon.
Questions 28-32
a) activation energy, Eact
b) standard entropy of formation, Sfo
c) enthalpy of reaction, ∆Hrxno
d) total entropy of change for the universe,
∆Souniverse
e) free energy of formation, ∆Gfo
28) Equals the energy difference between reactants
and the transition state
29) Is always greater than or equal to zero
30) Is defined as zero for pure elements in their
standard state
31) Indicates the amount of disorder in a pure
substance at the standard state
32) Is always negative for an exothermic reaction
33) Activation energy and enthalpy of reaction
data are listed, and one of these is wrong. Which
of these combinations is impossible?
f) Activation energy 100 kJ and an
enthalpy of reaction of +200 kJ
g) Activation energy 250 kJ and an
enthalpy of reaction of +200 kJ
h) Activation energy 200 kJ and an
enthalpy of reaction of -200 kJ
i) Activation energy 50 kJ and an
enthalpy of reaction of -200 kJ
j) Activation energy 250 kJ and an
enthalpy of reaction of +100 kJ
34) Refer to the diagram:
Which will be affected by the addition of a
catalyst?
I. A II. B III. C
a) I only b) II only c) III only
d) I and II e) II and III
36) In the Arrhenius equation, -Ea/RT, the
exponential factor represents
a) collision frequency b) activation energy
c) activated complex
d) fraction of molecules having energy of
activation
e) energy of activated complex
37) Based on the data below for a reaction in
which A and B react to form C, what is the rate
law for the reaction?
Initial Rate of
Formation of
[A] (mol L-1) [B] (mol L-1)
C (mol L-1 s-1)
0.2
0.2
0.50
0.4
0.2
2.00
0.8
0.2
8.00
0.2
0.4
1.00
0.2
0.8
2.00
a) rate = k [A] [B]
b) rate = k [A]2 [B]
c) rate = k [A] [B]2
d) rate = k [A]2 [B]2
e) rate = k [A]3
35) The activation energy for the reverse of the
reaction in the following diagram is
a) A—B b) B—C c) C—B d) C—A e) A—C
38) Rate = k [NO]2 [Cl2]
What is the order of the reaction with respect to
nitric oxide, NO?
a) 0 b) 1 c) 2 d) 3 e) 4
39) CO(g) + NO2(g) → CO2(g) + NO(g)
For the above reaction, the experimental rate law is
given as follows:
Rate = k [NO2]2
If additional CO gas is added to the reaction vessel,
while temperature remains constant, which of the
following is true?
a) Both the reaction rate and k increase.
b) Both the reaction rate and k decrease.
c) Both the reaction rate and k remain the same.
d) The reaction rate increases, but k remains the
same.
e) The reaction rate decreases, but k remains the
same.
**40) 2 NO ↔ N2O2 (fast equilibrium)
k1 for forward rate constant
k-1 for reverse rate constant
N2O2 + H2 → N2O + H2O (slow)
k2 for forward rate constant
N2O + H2 → N2 + H2O (fast)
k3 for forward rate constant
Nitric oxide, NO, can be reduced by hydrogen gas
to yield nitrogen gas and water vapor. The
decomposition is believed to occur according to
the reaction mechanism shown above. The rate
law for the reaction that is consistent with this
mechanism is given by which of the following?
a) Rate = k [NO]2
b) Rate = k [NO]2 [N2O2]
c) Rate = k [N2O2] [H2]
d) Rate = k [NO]2 [H2]
e) Rate = k [N2O] [H2]
41) 2 NO(g) + O2(g) → 2 NO2(g)
The reaction above occurs by the following two
step process:
Step I: NO(g) + O2(g) → NO3(g)
Step II. NO3(g) + NO(g) → 2 NO2(g)
Which of the following is true of Step II if it is the
rate-limiting step?
a) Step II has a lower activation energy and
occurs more slowly than Step I.
b) Step II has a higher activation energy and
occurs more slowly than Step I.
c) Step II has a lower activation energy and
occurs more quickly than Step I.
d) Step II has a higher activation energy and
occurs more quickly than Step I.
e) Step II has the same activation energy and the
same speed as Step I.
42) A plot of logarithm of reactant concentration
versus time is linear for
a) a zero-order reaction
b) a first-order reaction
c) a second-order reaction
d) a third-order reaction
e) none of the above
43) For the reaction A + 3 B → 4 C, the rate of
disappearance of B can be expressed as
a) 1/3 ∆[B]/∆t
b) –1/3 ∆[B]/∆t
c) –3/4 ∆[B]/∆t d) –4/3 ∆[B]/∆t
e) –1/4 ∆[B]/∆t
45) Which of the following is true for a zero-order
reaction?
a) The rate constant equals zero.
b) The activation energy equals zero.
c) The half-life time equals 0.693/k.
d) The rate is independent of
concentration.
e) The rate is independent of
temperature.
46) For the reaction 2 NO2 + O3 → N2O5 + O2, the
proposed mechanism is
Step 1 NO2 + O3 → NO3 + O2 (slow)
Step 2 NO3 + NO2 → N2O5 (fast)
The rate law for the reaction is
a) k [NO2] [O3]
b) k [NO3] [NO2]
c) k [NO3] [O2]
d) k [NO2]2 [O3]
e) more information is needed to determine the
rate law
44) Acetaldehyde decomposes when heated to
yield methane, CH4, and carbon monoxide, CO,
according to the following equation:
CH3CHO(g) → CH4(g) + CO(g)
Experimental data show that the rate increases by a
factor of four when the concentration of
acetaldehyde is doubled. The rate law for the
reaction
a) cannot be determined from the given
information
b) is rate = k [CH3CHO]
c) is rate = k [CH3CHO]2
d) is rate = k [CH3CHO]4
e) is rate = k4
47) The following graph represents the disappearance
of a reactant in a kinetics experiment. What is the
initial rate of disappearance of this reactant?
49) If a reactant concentration is doubled, and the
reaction rate increases by a factor of 8, the exponent
for that reactant in the rate law should be
a) ¼ b) ½ c) 2 d) 3 e) 4
a) 4 X10-3 mol L-1 s-1
c) 45 mol L-1 s-1
d) 0.022 mol L-1 s-1
b) 2.00 mol
e) 90
50) Which of the following is not commonly used as a
catatlyst?
a) NaCl b) Pt c) Au d) enzymes e) MnO2
51) The reaction 2 HgCl2 + C2O42- → 2Cl- + 2 CO2 +
Hg2Cl2(s) has a rate law of
Rate = k [HgCl2] [C2O42-]2
Overall this is a ________ -order reaction.
a) first b) second c) zero d) third e) fourth
48) A concentration-versus-time plot is curved for all
of the following except
f) a zero-order reaction
g) a first-order reaction
h) a second-order reaction
i) a third-order reaction
j) none of the above
52) Solid calcium carbonate decomposes to produce
solid calcium oxide and carbon dioxide gas. The value
of ∆Go for this reaction is 130.24 kJ/mole. Calculate
∆G at 100 oC for this reaction if the pressure of the
carbon dioxide gas is 1.00 atm.
a) –998.56 kJ/mole b) –604.2 kJ/mole
c) 56.31 kJ/mole
d) 130.24 kJ/mole
e) 256.24 kJ/mole
53) 2 NO(g) + 2 H2(g) → N2(g) + 2 H2O(g)
Which of the following is true regarding the relative
molar rates of disappearance of the reactants and
appearance of the products?
I. N2 appears at the same rate that H2 disappears
II. H2O appears at the same rate that NO disappears
III. NO disappears at the same rate that H2 disappears.
a) I only b) I and II only c) I and III only
d) II and III only
e) I, II, and III
54) If the temperature at which a reaction takes place is
increased, the rate of the reaction will
a) increase if the reaction is endothermic and
decrease if the reaction is exothermic
b) decrease if the reaction is endothermic and
increase if the reaction is exothermic
c) increase if the reaction is endothermic and
increase if the reaction is exothermic
d) decrease if the reaction is endothermic and
decrease if the reaction is exothermic
e) remain the same for both an endothermic and
an exothermic reaction
55) The reaction of elemental chlorine with ozone in
the atmosphere occurs by the two-step process shown
below.
I.
Cl + O3 → ClO + O2
II.
ClO + O → Cl + O2
Which of the statements below is true regarding this
process?
a) Cl is a catalyst b) O3 is a catalyst
c) ClO is a catalyst d) O2 is an intermediate
e) O is an intermediate
56) A set of reactants can follow two reaction paths.
One path produces “A” and the other produces “I”. At
30 oC, both “A” and “I” are produced at the same rate.
At 50 oC, “A” is produced faster than “I”. Which of
the following statements is true?
a) The two reaction paths have different values
for Ea.
b) Both reactions have the same Ea.
c) Ea for the reaction path for formation of I is
smaller than Ea for formation of A.
d) Differences in activation energy have no role
in the rate changes.
e) Both reaction rates should go up by a factor of
4 because T rose by 20 degrees.
Questions 57-60
A(g) + 2 B(g) + 3 C(g) → 4 D(g) + 5 E(g)
Rate of formation of E = d[E]/dt = k [A]2 [B]
57) If one were to double the concentration of B, the
rate of the reaction shown above would increase by a
factor of
a) ½ b) 1 c) 2 d) 4 e) 8
58) –d[B]/dt is equal to
a) –d[A]/dt b) –d[C]/dt c) +d ½ [D]/dt
d) +d 1/5 [E]/dt e) none of these
59) To decrease the rate constant k, one could
a) increase [E] b) decrease [B]
c) decrease the temperature
d) increase the volume
e) increase the pressure
60) If one were to reduce the volume of a container by
1/3, the rate of the reaction would increase by a factor
of
a) 3 b) 9 c) 16 d) 27
e) Reducing the volume of the container has no effect
on the rate.
61) Sulfur trioxide gas dissociates into sulfur dioxide
gas and oxygen gas at 1250 oC. In an experiment, 3.60
moles of sulfur trioxide were placed into an evacuated
3.0 liter flask. The concentration of sulfur dioxide gas
measured at equilibrium was found to be 0.20 M.
What is the equilibrium constant, Kc, for the reaction?
a) 1.6 X10-4 b) 1.0 X10-3 c) 2.0 X10-3
d) 4.0 X10-3 e) 8.0 X10-3
a)
b)
c)
d)
e)
It is zero order in [X].
It is first order in [X].
It is second order in [X].
It is first order in [Y].
The overall order of the reaction is 2.
63) N2(g) + O2(g) ↔ 2 NO
In the formation of NO (shown above), what effect will
the addition of a catalyst have on the equilibrium
constant, Keq, for the reaction. Assume temperature
and pressure remain constant.
a) A catalyst will increase Keq.
b) A catalyst will decrease Keq.
c) A catalyst will have no effect on Keq.
d) A catalyst will first increase Keq, until the
reaction slows, then Keq will decrease.
e) A catalyst will cause a dramatic increase in
Keq.
62) The graph above shows the results of a study of the
reaction of X with a large excess of Y to yield Z. The
concentrations of X and Y were measured over a
period of time. According to the results, which of the
following can be concluded about the rate law for the
reaction under the conditions studied?
64) All of the following are true about a boiling liquid
except
a) ∆Go must be zero b) ∆So must be positive
c) ∆Ho must be positive
d) Keq must be 1.00 e) ∆So must equal ∆Ho
65) The equilibrium law for the following reaction is
Na2CO3(s) + 2 HCl(g) ↔ H2O(l) + CO2(g)
a) [HCl]2 / [CO2]
b) [Na2CO3] [HCl]2 / {[H2O][CO2]}
c) [CO2] / [H2O]
d) [H2O][CO2] / {[Na2CO3][HCl]2}
e) [CO2] / [HCl]2
66) A reaction vessel contains N2(g), H2(g) and NH3(g) at
a certain temperature. If the equation is represented in
the following two ways,
N2(g) + 3 H2(g) ↔ 2 NH3(g)
½ N2(g) + 3/2 H2(g) ↔ NH3(g), then the
value of Kc
a) will be the same using either equation
b) will be larger when equation (ii) is used
c) will be larger when equation (i) is used
d) for (i) is equal to square of Kc value for (ii)
e) Both (b) and (d)
67) At 500 Kelvin, the Kp = 3.33 X10-17 for the
equilibrium reaction
N2(g) + 2 O2(g) → N2O4(g).
What is the value for Kp for the reaction
½ N2O4(g) → ½ N2(g) + O2(g)?
a) √3.33 X10-17 b) 3.19 X1019
c) (1/2) (3.33 X 10-17)
d) √(1/3.33 X10-17)
e) √3.33 X 10-17
70) N2(g) + 3 H2(g) ↔ 2 NH3(g) ∆Ho = -92 kJ
Which of the following changes would cause a
decrease in the equilibrium constant, Keq, for the
reaction shown above?
a) decrease the temperature
b) increase the temperature
c) increase the pressure of the reaction vessel by
decreasing the volume
d) the addition of nitrogen gas to the reaction
vessel
e) the addition of argon gas to the reaction vessel
68) PCl5(g) ↔ PCl3(g) + Cl2(g)
When PCl5 is placed in an evacuated container at 250
o
C, the above reaction takes place. The pressure in the
container before the reaction takes place is 6 atm and is
entirely due to the PCl5 gas. After the reaction comes
to equilibrium, the partial pressure due to Cl2 is found
to be 2 atm. What is the value of the equilibrium
constant, Kp, for this reaction?
a) 0.5 b) 1 c) 2 d) 5 e) 10
69) For which of the following reactions will the
equilibrium constants Kc and Kp have the same value?
a) 2 N2O5(g) ↔ 2 NO2(g) + O2(g)
b) 2 CO2(g) ↔ 2 CO(g) + O2(g)
c) H2O(g) + CO(g) ↔ H2(g) + CO2(g)
d) 3 O2(g) ↔ 2 O3(g)
e) CO(g) + Cl2(g) ↔ COCl2(g)
71) N2(g) + 3 H2(g) ↔ 2 NH3(g)
If 2.00 mol H2, 1.00 mol N2 and 2.00 mol NH3 are
placed into a 1.00 L evacuated flask. How will the
reaction above proceed if Kc = 0.105 at this
temperature?
a) The reaction must proceed from right to left.
b) The reaction must proceed from left to right.
c) The reaction is already at equilibrium, so no
net movement will occur.
d) The reaction cannot establish equilibrium at
this temperature.
e) The reaction will proceed from left to right
until 2.23 mol NH3 have been produced.
72) C(s) + CO2(g) ↔ 2 CO(g)
In the reaction shown above, the value of Kp is 167.5 at
a temperature of 1273 K. If the PCO2 at this
temperature is 0.10 atm (at equilibrium), what will the
PCO be?
a) 0.1 atm b) 4.1 atm c) 12.9 atm
d) 16.7 atm e) 53.0 atm
73) A reaction has an equilibrium constant of
3.8 X103. This constant will change if
a) a catalyst is added to the reaction mixture
b) additional reactant is added
c) the temperature is changed
d) the pressure is decreased
e) a precipitate is formed
74) Given the following reactions with their
equilibrium constants, calculate the equilibrium
constant for the overall reaction.
Cd2+ + 4 CN- ↔ Cd(CN)42- Kf = 7.7 X10+16
CdCO3 ↔ Cd2+ + CO32- Ksp = 1.8 X10-14
CdCO3 + 4 CN- ↔ Cd(CN)42- + CO32- Koverall=?
a) 1.4 X103 b) 4.3 X1030 c) 2.2 X106
d) 9.5 X102 e) 2.3 X10-31
75) 2 CO2(g) ↔ 2 CO(g) + O2(g) ∆Ho = -514 kJ
The equilibrium constant will be the highest when
the reaction above is carried out at
a) low temperature and low pressure
b) low temperature and high pressure
c) high temperature and high pressure
d) high temperature and low pressure
e) any temperature or pressure; neither affect the
reaction
76) H2(g) + I2(g) ↔ 2 HI(g)
At 450 oC the equilibrium constant, Kc, for the reaction
shown above has a value of 50. Which of the
following sets of initial conditions at 450 oC will cause
the reaction above to produce more H2?
I. [HI]= 5-molar, [H2]= 1-molar, [I2]= 1-molar
II. [HI]= 10-molar, [H2]= 1-molar, [I2]= 1-molar
III. [HI]= 10-molar, [H2]= 2-molar, [I2]= 2-molar
a) I only b) II only c) I and II only
d) II and III only e) I, II, and III
77) 4 FeS(s) + 7 O2(g) → 2 Fe2O3(s) + 4 SO2(g)
∆Ho = -2432 kJ mol-1
When the above reaction is at equilibrium for any
given pressure, P, and temperature, T, which of the
following will shift the position of equilibrium so that
more product is formed?
a) increase the temperature of the system without
changing the pressure
b) add an inert gas to increase the pressure of the
system
c) add a catalyst specific for the forward reaction
d) remove the Fe2O3 as it is formed
e) remove the SO2 as it is formed
78) 2 CO(g) + O2(g) ↔ 2 CO2(g) ∆Ho = -514.2 kJ
In the above reaction, which factors will cause the
equilibrium to shift to the right?
I. An increase in volume
II. An increase in temperature
III. Removal of CO2
a) I only b) II only c) III only
d) I and II only e) II and III only
79) Consider the reaction
2SO2(g) + O2(g) ↔ 2 SO3(g) ∆H = -198.2 kJ
Which of the following statements is NOT true?
a) Equilibrium will shift to the right if pressure is
increased.
b) Equilibrium will shift to the right if
temperature is decreased.
c) More SO3(g) can be produced by carrying the
reaction at high pressure and low temperature.
d) Equilibrium will shift to the left if temperature
is increased.
e) More SO3(g) can be produced if the reaction is
carried out at low pressure and high
temperature.
80) Which of the following does not necessarily
produce more product in a chemical reaction?
a) increasing the temperature
b) increasing the amount of reactants
c) removing product as it is formed
d) decreasing the volume of a reaction where ∆n
is negative
e) increasing the volume of a reaction where ∆n
is positive
Questions 81-82
2 SO2(g) + O2(g) ↔ 2 SO3(g) ∆H = -197 kJ
81) Starting with a system at equilibrium, which of the
following operations will not increase the amount of
SO3(g)?
a) decreasing the temperature of the reaction
vessel
b) decreasing the volume of the reaction vessel
c) adding N2(g) to increase the pressure in the
reaction vessel
d) adding O2(g) to the reaction vessel
e) adding SO2(g) to the reaction vessel
82) SO2 and O2 are mixed in an insulated vessel and
sealed so that there is no heat exchange with the
surroundings. When the reaction comes to equilibrium,
what best describes what has happened to the system?
Use the information from the previous question if
needed.
a) Total energy remains constant and the entropy
increases.
b) Total energy increases and the entropy remains
constant.
c) Total energy remains constant and the
temperature of the system increases.
d) Total energy decreases and the temperature
increases.
e) Total energy remains constant and the
temperature decreases.
83) 2 NO(g) + O2(g) ↔ 2 NO2(g) ∆H < 0
Which of the following changes alone would cause a
decrease in the value of Keq for the reaction represented
above?
a) decreasing the temperature
b) increasing the temperature
c) decreasing the volume of the reaction vessel
d) increasing the volume of the reaction vessel
e) adding a catalyst
84) 2 SO3(g) ↔ 2 SO2(g) + O2(g)
After the equilibrium represented above is established,
some pure O2(g) is injected into the reaction vessel at
constant temperature. After equilibrium is
reestablished, which of the following has a lower value
compared to its value at the original equilibrium?
a) Keq for the reaction
b) The total pressure in the reaction vessel
c) The amount of SO3(g) in the reaction vessel
d) The amount of O2(g) in the reaction vessel
e) The amount of SO2(g) in the reaction vessel
Written Questions:
1) 2 NO(g) + Cl2(g) → 2 NOCl(g)
The following data were collected for the reaction above. All of the measurements were taken
at a temperature of 263 K.
Experiment Initial [NO]
Initial [Cl2]
Initial rate of disappearance
(M)
(M)
of Cl2 (M/min)
1
0.15
0.15
0.60
2
0.15
0.30
1.2
3
0.30
0.15
2.4
4
0.25
0.25
?
a) Write the expression for the rate law for the reaction above.
b) Calculate the value of the rate constant for the above reaction and specify the units.
c) What is the initial rate of appearance of NOCl in experiment 2?
d) What is the initial rate of disappearance of Cl2 in experiment 4?
2) The reaction between NO and H2 is believed to occur in the following three-step process.
NO + NO ↔ N2O2 (fast)
N2O2 + H2 → N2O + H2O (slow)
N2O + H2 → N2 + H2O (fast)
a) Write a balanced equation for the overall reaction.
b) Identify the intermediates in the reaction. Explain your reasoning.
c) From the mechanism represented above, a student correctly deduces that the rate law for the
reaction is rate = k [NO]2[H2]. The student then concludes that (1) the reaction is third
order and (2) the mechanism involves the simultaneous collision of two NO molecules and
an H2 molecule. Are conclusions (1) and (2) correct? Explain.
d) Explain why an increase in temperature increases the rate constant, k, given the rate law in
(c).
3) 2 A + B → C + D
The following results were obtained when the reaction represented above was studied at 25 oC.
Experiment Initial
Initial
Initial rate of formation
[A]
[B]
of C (mol L-1 min-1)
1
0.25
0.75
4.3 X10-4
2
0.75
0.75
1.3 X10-3
3
1.50
1.50
5.3 X10-3
4
1.75
?
8.0 X10-3
a) Determine the order of the reaction with respect to A and to B. Justify your answer.
b) Write the rate law for the reaction. Calculate the value of the rate constant, specifying units.
c) Determine the initial rate of change of [A] in Experiment 3.
d) Determine the initial value of [B] in Experiment 4.
e) Identify which of the reaction mechanisms represented below is consistent with the rate law
developed in part (b). Justify your choice
Choices:
1. A + B → C + M fast
M+A→D
slow
2. B ↔ M
fast equilibrium
M + A → C + X slow
A+X→D
fast
3. A + B ↔ M
M+A→C+X
X→D
fast equilibrium
slow
fast
4) Answer the following questions regarding the kinetics of chemical reactions.
a) The diagram below shows the energy pathway for the reaction
O3 + NO → NO2 + O2.
Clearly label the following directly on the diagram.
(i) The activation energy (Ea) for the forward reaction.
(ii) The enthalpy change (∆H) for the reaction.
b) The reaction 2 N2O5 → 4 NO2 + O2 is first order with
respect to N2O5.
(i) Using the axes below, complete the graph that represents the change in [N2O5] over time as
the reaction proceeds.
(ii) Describe how the graph in (i) could be used to find the reaction rate at a given time, t.
(iii) Considering the rate law and the graph in (i), describe how the value of the rate constant, k,
could be determined.
(iv) If more N2O5 were added to the reaction mixture at constant temperature, what would be the
effect on the rate constant, k? Explain.
c) Data for the chemical reaction 2 A → B + C were collected by measuring the
concentrations of A at 10-minute intervals for 80 minutes. The following graphs were
generated from the analysis of the data.
Use the information in the graphs above to answer the following.
(i) Write the rate-law expression for the reaction. Justify your answer.
(ii) Describe how to determine the value of the rate constant for the reaction.
5) (I) A2 + B2 → 2 AB
(II) X2 + Y2 → 2 XY
Two reactions are represented above. The potential-energy diagram for reaction I is shown
below. The potential energy of the reactants in reaction II is also indicated on the diagram.
Reaction II is endothermic, and the activation energy of reaction I is greater than that of
reaction II.
a) Complete the potential-energy diagram for reaction II on the graph above.
b) For reaction I, predict how each of the following is affected as the temperature is increased
by 20 oC. Explain the basis for each prediction.
(i)
Rate of Reaction
(ii)
Heat of Reaction
c) For reaction II, the form of the rate law is rate = k [X2]m[Y2]n. Briefly describe an
experiment that can be conducted in order to determine the values of m and n in the rate law
for the reaction.
d) From the information given, determine which reaction initially proceeds at the faster rate
under the same conditions of concentration and temperature. Justify your answer.
6) Hydrogen peroxide decomposes according to the following reaction:
H2O2(aq) → 2 H2O(l) + O2(g)
A graph of concentration versus time for a 1.00 M solution of H2O2 is shown below:
a) How can you determine the instantaneous rate
at 4,000 sec?
b) What is the approximate value of half-life as it
is read from the graph?
c) Assuming that decomposition of H2O2 is a
first-order reaction, how can you determine the
rate constant (k) from the half-life?
7) C(s) + H2O(g) ↔ CO(g) + H2(g) ∆Ho = +131 kJ
A rigid container holds a mixture of graphite pellets (C(s)), H2O(g), CO(g) and H2(g) at equilibrium. State
whether the number of moles of CO(g) in the container will increase, decrease, or remain the same after each
of the following disturbances is applied to the original mixture. For each case, assume that all other
variables remain constant except for the given disturbance. Explain each answer with a short statement.
a) Additional H2(g) is added to the equilibrium mixture at constant volume.
b) The temperature of the equilibrium mixture is increased at constant volume.
c) The volume of the container is decreased at constant temperature.
d) The graphite pellets are pulverized.
8) Le Chatlier’s principle is central to many qualitative and quantitative aspects of chemical equilibrium.
Use the following equation to answer the questions.
N2(g) + 3 H2(g) ↔ 2 NH3(g) (∆Ho = -46.0 kJ mol-1)
a) Briefly but completely summarize Le Chatlier’s principle.
b) Which changes in concentration will increase the amount of NH3 produced?
c) What changes in pressure will not increase the amount of NH3 produced?
d) How should the temperature be changed to increase the amount of NH3 produced?
e) Will a catalyst increase the amount of NH3 produced?
f) What will happen if liquid water is present in the reaction system?
9) Hydrogen bromide decomposes according to the equation 2 HBr(g) ↔ H2(g) + Br2(g)
a) Write the equilibrium law in terms of concentrations, Kc, and partial pressures, Kp.
b) A 55.5 g sample of HBr (molar mass = 80.9) is transferred to an evacuated 22.0 L flask at 142 oC.
(1) What is the initial concentration in moles per liter of HBr? (2) What is the initial pressure of
HBr in mm Hg?
c) When the system comes to equilibrium, 22.4 g of Br2 is found to be in the flask. Calculate the value
of Kc and Kp. Be sure to indicate whether you are calculating Kc or Kp.
d) At another temperature, Kc = 17.7. 1.37 mol HBr(g), 2.31 mol H2(g), and 0.551 mol Br2(g) are
introduced into an evacuated 15.0 L flask. Determine whether the reaction proceeds in the forward
or in the reverse direction.
10) H2(g) + CO2(g) ↔ H2O(g) + CO(g)
When H2(g) is mixed with CO2(g) at 2000 K, equilibrium is achieved according to the equation above. In one
experiment, the following equilibrium concentrations were measured.
[H2] = 0.20 mol/L [CO2] = 0.30 mol/L [H2O] = [CO] = 0.55 mol/L
a) What is the mole fraction of CO(g) in the equilibrium mixture?
b) Using the equilibrium concentrations given above, calculate the value of Kc, the equilibrium
constant for the reaction.
c) Determine Kp in terms of Kc for this system.
d) When the system is cooled from 2000K to a lower temperature, 30.0 percent of the CO(g) is
converted back to CO2(g). Calculate the value of Kc at this lower temperature.
e) In a different experiment, 0.50 mole of H2(g) is mixed with 0.50 mole of CO2(g) in a 3.0 liter reaction
vessel at 2000 K. Calculate the equilibrium concentration, in moles per liter, of CO(g) at this
temperature.
11) The rate of decomposition of di-tert-butyl peroxide (DTBP) to acetone and ethane:
(CH3)3COOC(CH3)3(g) → 2 (CH3)2CO(g) + CH3CH3(g)
DTBP
acetone
ethane
The progress of the reaction can be followed by measuring the total pressure in a closed system at constant
temperature. The following data were collected in one experiment.
Time, s
Ptotal, mm Hg
0
700
0.50 X104
1420
1.00 X104
1770
1.50 X104
1940
2.00 X104
2020
2.50 X104
2062
a) What is the partial pressure PDTBP at the beginning, t = 0, of the experiment before any
decomposition?
b) What is PDTBP at t = ∞? (Assume the reaction goes to completion.)
c) What is Ptotal at t = ∞?
d) What is PDTBP at t = 0.50 X104?
e) What is the half-life for the decomposition reaction?
f) What is the order for the reaction?
12) Consider the dimerization reaction of NO2: 2 NO2(g) ↔ N2O4(g)
a) Using Lewis structures, suggest why NO2 dimerizes and CO2 does not.
b) What is the sign of the entropy change, ∆So, for this reaction in the forward direction?
c) At 100 oC the value of Kc is approximately 3.3. What is the sign for ∆Ho?
d) Can the reverse reaction be made spontaneous? If so how?
13) For the gaseous equilibrium represented below, it is observed that greater amounts of PCl3 and Cl2 are
produced as the temperature is increased.
PCl5(g) ↔ PCl3(g) + Cl2(g)
a) What is the sign of ∆So for the reaction? Explain.
b) What change, if any, will occur in ∆Go for the reaction as the temperature is increased? Explain
your reasoning in terms of thermodynamic principles.
c) If He gas is added to the original reaction mixture at constant volume and temperature to half the
original volume, what will happen to the partial pressure of Cl2? Explain.
d) If the volume of the reaction mixture is decreased at constant temperature to half the original
volume, what will happen to the number of moles of Cl2 in the reaction vessel? Explain.
14) C2H2(g) + 2 H2(g) → C2H6(g)
Information about the substances involved in the reaction represented above is summarized in the following
tables.
Substance
So (J/mol•K) ∆Hfo (kJ/mol)
Bond
Bond Energy (kJ/mol)
C2H2(g)
200.9
226.7
C—C
347
H2(g)
130.7
0
C==C
611
C2H6(g)
-----84.7
C—H
414
H—H
436
a) If the value of the standard entropy change, ∆So, for the reaction is –232.7 joules per mole• Kelvin,
calculate the standard molar entropy, So, of C2H6 gas.
b) Calculate the value of the standard free-energy change, ∆Go, for the reaction. What does the sign of
∆Go indicate about the reaction above?
c) Calculate the value of the equilibrium constant, K for the reaction at 298 K.
d) Calculate the value of the C==C (triple) bond energy in C2H2 in kilojoules per mole.