Name _____________________
Period _____
Advanced Chemistry Practice Problems – Kinetics!!!
1. The gas-phase reaction of nitric oxide and bromine yields nitrosyl bromide:
2NO(g) + Br2(g) -> 2NOBr(g)
The rate law is rate=k[NO][Br2].
a. What is the order with respect to NO
b. What is the order with respect to Br2?
c. What is the overall reaction order?
2. The reaction of hydrogen and iodine monochloride is first order in H2 and second order
in ICl.
H2(g) + 2ICl(g) -> 2HCl(g) + I2(g)
a. What is the rate law?
b. What are the units of the rate constant?
3. Use the following data to answer the following questions about the decomposition of
N2O5.
Time (s)
0
100
200
300
400
500
600
700
[N2O5] (M)
0.02
0.0169
0.0142
0.012
0.0101
0.0086
0.0072
0.0061
Log [N2O5]
-1.699
-1.772
-1.848
-1.921
-1.996
-2.066
-2.143
-2.215
Question 4 Graph 2
Question 4 Graph 1
200
200
400
-1.9
-2.1
600
800
1/[N2O5]
Log [N2O5]
-1.5
-1.7 0
1/[N2O5]
50
59.1716
70.42254
83.33333
99.0099
116.2791
138.8889
163.9344
150
100
50
Series1
0
0
-2.3
Time (s)
200
400
600
800
Time (s)
a. What is the order of the reaction? Please explain how you arrived at your
answer!
b. What is the rate law for this reaction?
c. What is the value of the rate constant?
d. What is the molarity of N2O5 after 265 s?
e. How long does it take for the concentration of N2O5 to drop to 0.0226 M?
4. Nitrogen dioxide decomposes to nitric oxide and molecular oxygen:
2NO2(g) -> 2NO(g) + O2(g)
Use the following data to answer the following questions.
Time (s)
0
50
100
150
200
300
400
500
[NO2] (M)
0.008
0.00658
0.00559
0.00485
0.00429
0.00348
0.00293
0.00253
Log [NO2]
-2.097
-2.182
-2.253
-2.313
-2.367
-2.458
-2.533
-2.597
Question 3 Graph 1
400
300
200
100
0
Log [NO2]
1/[NO2] (1/M)
Question 3 Graph 2
0
100
200
300
1/[NO2]
125
152
179
206
233
287
341
395
400
500
-2.1
0
200
400
600
-2.3
-2.5
-2.7
Time (s)
Time (s)
a. Is the reaction first order or second order? Explain your answer.
b. Calculate the value of the rate constant.
c. What is the concentration of NO2 at t=25 minutes?
d. What is the half-life of the reaction when the initial concentration of NO2 is
0.003 M?
f. What is t1/2 when [NO2]o is 0.005 M?
5. What step in a reaction mechanism is the rate-determining step (fastest or slowest)?
6. What is the Arrhenius equation and what can you find out about a reaction from the
equation?
7. Draw two potential energy profiles, one for a catalyzed reaction and one for an
uncatalyzed reaction. Label activation energy, change in energy, and the x and y axis.
Practice Problems - Chemical Equilibrium!!!
1. What are the units for K?
2. Write the equilibrium constant for the following reactions:
a. 2NO(g) + Br2(g) -> 2NOBr(g) K = 2.2 x 104
b. H2(g) + 2ICl(g) -> 2HCl(g) + I2(g) K = 8.6 x 10-2
3. Using the reactions in Question 2, when the reactions come to equilibrium does the
equilibrium mixture contain mostly reactants or mostly products?
a.
b.
4. Once again, use the reactions in Question 2 to write the expression for Kp for each
reaction.
a.
b.
5. Write the expression for Kc for each reaction in Question 2.
a.
b.
6. The equilibrium constant K = 7.9 x 105 for the reaction:
2NO(g) + O2(g) <=> 2NO2(g)
a. Given the concentrations of NO, O2 and NO2 are 0.25 M. Find the reaction
quotient (Qc).
b. Is the reaction at equilibrium? If not, in which direction does the reaction
proceed?
7. The equilibrium constant K = 1.2 x 10-42 for the reaction:
H2(g) <=> 2H(g)
a. Using the K are the reactants or the products favored?
b. What is the molar concentration of H atoms if [H2] = 0.12 M at equilibrium?
8. Given K = 2.06 for the reaction:
CO(g) + H2O(g) <=> CO2(g) + H2(g)
a. What are the equilibrium concentrations of CO2 and H2O if the initial
concentrations of reactants are 0.25 M?
9. The equilibrium constant K = 1.7 x 10-3 for the reaction:
N2(g) + O2(g) <=> 2NO(g)
a. If the initial concentrations of the reactants are 0.20 M for N2 and 0.50 M for
O2, what are the concentrations of NO, N2 and O2 when the reaction mixture
reaches equilibrium?
10. For the following reaction;
N2(g) + 3H2(g) <=> 2NH3(g)
a. Using Le Chatelier’s principle predict the direction of the reaction if you
increase [N2] or [H2]
Thermochemistry/Chemical Energy – Practice Problems
1. Calculate (in Joules) the work done by a chemical reaction if the volume increases
from 3.2 L to 3.4 L against a constant external pressure of 3.6 atm. What is the sign of
the energy change?
2. What is the sign of
H for an exothermic reaction? For an endothermic reaction?
3. Under what circumstances are
H and
E nearly equal?
4. Used in welding metals, the reaction of acetylene with oxygen has H = -1255.5 kJ.
How much P-V work is done in kJ and what is the value of E in kJ for the reaction of
5.25 g of acetylene at 2 atm if the volume change is -2.8 L?
C2H2(g) + 5/2O2(g) -> H2O(g) + 2CO2(g) H = -1255.5 kJ
5. Titanium metal is used as a structural material in many high-tech application such as
in jet engines and bicycles. What is the specific heat of titanium in J/(g· C) if it takes
89.8 J to raise the temperature of 33.0 g block by 5.21 C?
6. Describe Hess's law, why does it work, and what is a compound's standard heat of
formation?
7. Calculate
H f for benzene, C6H6, in kJ/mol from the following data:
2C6H6(l) + 15 O2(g) -> 12CO2(g) + 6H2O(l) H = -6534 kJ
H f(CO2) = -393.5 kJ/mol
H f(H2O) = -285.8 kJ/mol
8. If it takes 1200 J of energy to inflate a balloon from 1L to 2L against an external
pressure of 0.9 atm, is more energy required to inflate it or to do the PV work against the
atmosphere? Show how much more through calculations.
9. Vinyl chloride (H2C=CHCl), the starting material used in the preparation of polyvinyl
chloride, is prepared by a two step process that begins with the reaction of Cl2 with
ethylene to yield ethylene dichloride:
Cl2(g) + H2C=CHCl(g) -> ClCH2CH2Cl(l)
H = -217.5 kJ/mol
Is the reaction endothermic or exothermic?
10. When 1.50 g of magnesium metal is allowed to react with 200 mL of 6 M HCl, the
temperature rises from 25 C to 42.9 C. Calculate H in kJ for the reaction, assuming
that the heat capacity of the calorimeter is 776 J/ C, that the specific heat of the final
solution is the same as that of water [4.18J/( g· C)], and that the density of the solution is
1.00 g/mL.
Gas – Practice Problems
1. Carry out the following conversions!
a. 4.81 atm to pascals
b. 30.01 inches to atm
2. Why is atmospheric pressure less at the top of mountain than at sea level (~1
atm)?
3. Briefly describe the following gas laws - use equations as much as possible!
a. Boyle’s Law:
b. Charles’ Law:
c. Avogadro’s Law:
4. What conditions are defined as standard temperature and pressure?
5. What are two characteristics/assumptions about real gases that cause the
predictions of the ideal-gas law to vary from actual values?
6. If 2.5 g of the vapor of a volatile liquid is able to fill 264.2-mL flask at 91 C and
745 mm Hg:
a. What is the molar mass of the liquid
b. What is the density of the vapor under these conditions?
7. The liquids used in the Vapor Pressure Lab were insoluble in water. What effect
would be seen if the liquids tested by this method were soluble in water? For
example, ethanol is fairly volatile but is also completely miscible with water in all
proportions.
8. What is the difference between effusion and diffusion?
9. Briefly describe Dalton’s law of partial pressure!
10. A typical high-pressure tire on a road bicycle has a volume of 375 mL and a
pressure of 130 psi (lb/in2) at 25 C. Suppose the rider filled the tire with helium
to minimize weight. What would be the mass of helium in the tire?
11. If 15.0 g of CO2 gas has a volume of 0.30 L at 300 K, what is its pressure in mm
Hg?
12. How many moles of air are there in the lungs of an average adult with a total lung
capacity of 4.0 L? Assume that the person is at 1.0 atm pressure (On a nice
Hawaiian beach) and has a normal body temperature of 98.6 C. Use your own
pulse if necessary!
Liquids and Solids – Practice Problems
1. Label each of the following forces as either intermolecular or intra molecular!
a. Hydrogen bond
b. Covalent bond
c. Ionic bond
d. London dispersion
e. Dipole-dipole
2. What type of force explains the unique properties of water; such as surface
tension and capillary action?
3. A topaz crystal has a lattice spacing (d) of 1.5 A (1A = 1.x10-10m). Calculate the
wavelength of X-ray that should be used if = 16 (assume n=2).
4. Based on their properties, classify each of the following as to the type of solid it
forms (molecular, network, or ionic):
a. diamond
b. NaCl
c. Cl2
d. C2H4
e. Graphite
5. Steel is formed by mixing iron and carbon. Carbon fills the gaps between the iron
atoms making steel stronger by preventing the iron atoms from moving. What
type of alloy is steel?
Interstitial
or
Substitutional
6. How does the vapor pressure of a pure liquid vary with temperature?
7. Metals are ductile, malleable, and good conductors of heat and electricity.
Describe or give an example of the following characteristics.
a. Ductile =
b. Malleable =
c. Conductors of heat/electricity =
8. Calculate the vapor pressure of propanol at 53 C if the heat of vaporization is 50
kJ/mol and the vapor pressure is 15 C at 10 torr.
9. On a phase diagram…be able to identify the following!
a. Identify the triple point.
b. Identify the normal boiling point.
c. Identify the normal freezing point.
d. Identify the critical point.
e. Which phase is denser, solid or liquid?