© 2004 PECK page1
EXAM 1
1.
CHEMISTRY 102
(previous exam)
Spring 2004
Which of the following statements is incorrect about the reaction having this rate law
expression: Rate = k[A]2[B]?
(a)
(b)
(c)
(d)
(e)
Doubling the concentration of A doubles the rate.
The reaction is first order in B.
The reaction is overall third order.
The reaction is second order in A.
A and B must both be reactants.
2.
Which one of the following statements about collision and transition state theory is false?
(a) Reactants must collide to form products.
(b) All reactant collisions result in product formation.
(c) Activation energy is always positive.
(d) Reacting molecules must absorb energy to form the transition state.
(e) Reactant collisions must be properly orientated to form products.
3.
Given the following at 25°C, calculate ∆H f0 for HPO3(s) at 25°C.
0
P4O10(s) + 4HNO3(l) → 4HPO3(s) + 2N2O5(s) ∆Hrxn = –180.6 kJ
∆Hf0 (kJ / mol)
Substance
P4O10(s)
–2984
HNO3(l)
–174.1
N2O5(s)
–43.1
(a) –528.0 kJ/mol
(b) –1474 kJ/mol
(c) –948.5 kJ/mol
(d) +1474 kJ/mol
(e) –943.7 kJ/mol
4.
How much heat is evolved in the formation of 35.0 grams of Fe2O3(s) at 25°C and
1.00 atm pressure by the following reaction?
4Fe(s) + 3O2(g) → 2Fe2O3(s)
0
∆Hf (kJ/mol)
0
(a) 90.4 kJ
(b) 180.7 kJ
5.
Given that
2H2(g) +
0
(c) 151 kJ
–824.2
(d) 360.1 kJ
0
(e) 243. 9 kJ
O2(g) → 2H2O(l)
∆Hrxn
= –571.7 kJ/rxn
C3H4(g) + 4O2(g) → 3CO2(g) + 2H2O(l)
0
∆Hrxn
0
∆Hrxn
= –1941 kJ/rxn
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l)
= –2220 kJ/rxn
Determine the heat of the following hydrogenation reaction:
C3H4(g) + 2H2(g) → C3H8(g)
(a) – 293 kJ/mol (b) 1422 kJ/mol (c) –864 kJ/mol (d) – 1422 kJ/mol (e) 864 kJ/mol
© 2004 PECK page2
6.
Which statement is false?
(a) The thermodynamic quantity most easily measured in a "coffee cup" calorimeter
is ∆H.
(b) No work is done in a reaction occurring in a bomb calorimeter.
(c) ∆H is sometimes exactly equal to ∆E.
(d) ∆H is often nearly equal to ∆E.
(e) ∆H is equal to ∆E for the following process: 2H2(g) + O2(g) → 2H2O(g)
7.
Calculate the ∆G 0f at 298 K for PbCl2(s) from the following information. ∆G0 for
the reaction below is –58.4 kJ at 298 K.
PbS(s) + 2HCl(g) → PbCl2(s) + H2S(g)
0
–98.7
–95.30
?
–33.6
∆Gf (kJ/mol)
(a) –16.0 kJ/mol (b) –47.6 kJ/mol (c) –52.3 kJ/mol (d) –314.1 kJ/mol (e) –36.2 kJ/mol
8.
Given the following data for the NH4+ + NO2– → N2 + 2H2O reaction
[NO2–]
Rate
[NH4+]
0.010 M
0.020 M
0.020 M/s
0.015
0.020
0.030
0.010
0.010
0.005
The rate law for the reaction is
(b) R = k[NH4+]2[NO2–]
(c) R = k[NH4+]2[NO2–]2
(a) R = k[NH4+][NO2–]
(e) None of the above
(d) R = k[NH4+][NO2–]2
9.
When 4.168 kJ of heat was added to a calorimeter containing 75.40 g of water, the
temperature of the water increased from 24.58 °C to 35.82 °C. Based on these data,
calculate the heat capacity of the calorimeter (in J/°C). The specific heat of water is 4.184
J/g•°C.
(a) 622 J/°C (b) 55.34 J/°C (c) 315.5 J/°C (d) 25.31 J/°C (e) 17.36 J/°C
10.
Which one of the following statements is false?
(a)
(b)
(c)
(d)
(e)
11.
A coffee-cup calorimeter measures ∆H directly.
The change in internal energy, ∆E, for a process is equal to the amount of heat
transferred at constant volume, qv.
The change in enthalpy, ∆H, for a process is equal to the amount of heat transferred
at constant pressure, qp.
If qp for a process is negative, the process must be exothermic.
The work done in a process occurring at constant pressure is zero if ∆ngases is one.
Which one of the following statements is not correct?
(a)
When ∆G for a reaction is negative, the reaction is spontaneous.
(b)
When ∆G for a reaction is positive, the reaction is nonspontaneous.
(c)
When ∆G for a reaction is zero, the system is at equilibrium.
(d)
When ∆H for a reaction is negative, the reaction is never spontaneous.
(e)
When ∆H and ∆S for a reaction are both positive, the reaction can be
spontaneous at high temperatures.
© 2004 PECK page3
Given the following potential energy diagram for the one-step reaction
X + Y → Z + R
The arrow "c" represents the __________.
Potential energy
12.
b
a
c
x+y
z+R
Reaction coordinate
(a) net energy of reaction for the forward reaction
(b) activation energy for the forward reaction
(c) net energy of reaction for the reverse reaction
(d) activation energy for the reverse reaction
(e) energy content for the reaction
13.
Which of the following is a kinetic quantity?
(a) enthalpy
(b) internal energy
(d) rate of reaction
(e) entropy
(c) free energy
14.
The units of the rate constant for an overall first order reaction can be _________.
(a) M–1•s–1
(b) M
(c) M•s–1
(d) s–1
(e) M2•s–1
15.
The heat of reaction of one of the following reactions is the average bond energy for the
N-H bond in NH3. Which one
(a) 2NH3(g) → N2(g) + 3H2(g)
(b) NH3(g) → 1/2N2(g) + 3/2H2(g)
(c) 2/3NH3(g) → 1/3N2(g) + H2(g)
(d) 1/3NH3(g) → 1/3N(g) + H(g)
(e) 1/3N(g) + H(g) → 1/3NH3(g)
16. The gas phase reaction 2A2(g) + B2(g) → 2A2B(l) has a reaction rate which is
experimentally observed to follow a rate law expression of rate = k[A]2[B]. If the
concentration of A is tripled and the concentration of B is doubled, the reaction
rate would be increased by a factor of ____.
(a) 6
(b) 9
(c) 12
(d) 18
(e) 36
17. Which statement is incorrect?
(a)
Energy is the capacity to do work or to transfer heat.
(b) Kinetic energy is the energy of motion.
(c)
Potential energy is the energy that a system possesses by virtue of its position
or composition.
(d) The Law of Conservation of Energy is another statement of the First Law of
Thermodynamics.
(e)
A process that absorbs energy from its surroundings is called exothermic.
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18. Joseph Priestley prepared oxygen by heating mercury(II) oxide. The compound HgO is stable
at room temperature but decomposes into its elements (Hg and O2) at high temperatures.
What conclusions can be drawn concerning ∆H and ∆S for this decomposition reaction?
(a)∆H is negative and ∆S is positive.
(b) ∆H is positive and ∆S is positive.
(c)∆H is negative and ∆S is negative.
(d) ∆H is positive and ∆S is negative.
(e)∆H becomes negative at high temperatures.
19. Which response contains all the processes below for which ∆S is positive and none for
which ∆S is negative?
I.
CCl4(l) → CCl4(g)
II. N2(g) + 3H2(g) → 2NH3(g)
III. 2N2O(g) → 2N2(g) + O2(g)
IV. I2(g) → I2(s)
(a) I and II
(b) III and IV
(c) II and IV
(d) I and III
(e) I, II, and IV
20. Which of the following statements is incorrect?
(a) The reaction rate for a zero-order reaction is independent of concentrations.
(b) The specific rate constant for a second-order reaction is independent of temperature.
(c) The half-life for a first-order reaction is independent of initial concentrations.
(d) The rate-law expression relates rate and concentration.
(e) Nuclear decay follows first-order kinetics.
Answers: 1. (a), 2. (b), 3. (e), 4. (b), 5. (a), 6. (e), 7. (d), 8. (d), 9. (b), 10. (e), 11. (d),
12. (d), 13. (d), 14. (d), 15. (d), 16. (d), 17. (e), 18. (b), 19. (d), 20. (b)