AP Chemistry
Semester 1
Exam Review
Topics Covered will be:
Stoichiometry, Equations & Chemical Reactions, Thermodynamics, Kinetics, Equilibrium,
Measurement including units & error
AP Chemistry Semester Exam review
1.
Calculate the molar solubility of barium sulfate, BaSO4, in 0.020 M sodium sulfate, Na2SO4. Ksp for BaSO4 is
1.08 x 10-10
A. 1.04 x 10-5
B. 5.4 x 10-5
C. 7.87 x 10-8
D. 5.4 x 10-9
2.
Determine the standard enthalpy of reaction for the combustion of hydrogen sulfide gas, which proceeds according to the
reaction shown:
2H2S(g) + 3O2(g) → 2H2O(l) + 2SO2(g)
The standard enthalpies for the constituents are as follows:
Formula
ΔH°f (kJ mol-1)
A.
3.
H2S(g)
-20
H2O(l)
-285.8
SO2(g)
-296.8
-575 kJ
For the reaction
Experiment
A.
B.
C.
D.
B. -726 kJ
2A
+
C. -963 kJ
B
→
D. -1125 kJ
C , experimental data was collected for 3 trials:
[A] M
[B] M
Initial rate M s-1
1
0.40
0.20
5.5 x 10-3
2
0.80
0.20
5.5 x 10-3
3
0.40
0.40
2.2 x 10-2
Rate = k[A][B]
Rate = k[A]0[B]2
Rate = k[A]2[B]2
Rate = k[A]2[B]0
4.
4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)
In the above reaction, 3.10 g of NH3 reacts with 2.50 g of O2. What is the theoretical yield of NO?
A. 1.88 g
B. 5.46 g
C. 8.20 g
D. 24.0 g
5.
H2O(g) + Cl2O(g) ↔ 2HOCl(g)
The reaction above is allowed to come to equilibrium at room temperature. At equilibrium, the partial pressure of H 2O is
296 mm Hg, Cl2O is 15 mm Hg, and HOCl is 20 mm Hg. What is the value of K p at this temperature?
A. 222
B. 11
C. 0.017
D. 0.090
6.
Which of the following reactions involves the largest increase in entropy?
A. AgNO3(aq) + HCl(aq) → AgCl(s) + HNO3(aq)
B. N2(g) + O2(g)
→
C. 2NO(g) + O2(g)
D. 2KClO3(s)
→
2NO(g)
→
2NO2(g)
2KCl(s) + 3O2(g)
7.
You are supposed to prepare 250 ml of a 0.1 M solution of Pb(NO3)2 solution (molar mass = 331.2 g). You would need
to mix ____ of Pb(NO3)2 with enough water to make 250 ml of solution.
A. 331.2 g
B. 33.12 g
C. 8.28 g
D. 3.312 g
8.
Step 1:
NO(g) + Cl2(g) ↔
NOCl2(g)
fast
Step 2:
NO(g) + NOCl2(g) → 2NOCl(g)
slow
Which of the following rate laws is consistent with the reaction mechanism shown above?
A. Rate = k[NO][Cl2]
B. Rate = k[NO]2
C. Rate = k[NO][NOCl2]
D. Rate = k[NO]2[Cl2]
9.
__C6H5OH + __O2 → __CO2 + __H2O
When the equation above is balanced, how many water molecules will be produced?
A. 1
B. 2
C. 3
D. 4
10.
What is the percentage composition of Mg in the compound Mg3(PO4)2?
A. 21.92%
B. 23.57%
C. 27.74%
D. 32.32%
11.
For the reaction A + B → C + D , ΔH° = +40 kJ and ΔS° = +50 JK -1. Therefore, the
reaction under standard conditions is
A. Spontaneous at temperatures less than 10 K
B. Spontaneous at temperatures greater than 800 K
C. Spontaneous only at temperatures between 10 K and 800 K
D. Spontaneous at all temperatures
12.
In which of the following systems would the number of moles of the substances present at equilibrium NOT be shifted
by a change in the volume of the system at constant temperature?
A. SO2(g) + O2(g) ↔ 2SO3(g)
↔
B. N2(g) + 3H2(g)
C. NO2(g) + SO2(g)
D. N2O4(g)
↔
2NH3(g)
↔
SO3(g) + NO(g)
2NO2(g)
13.
A 0.4647 g sample of a compound containing only carbon, hydrogen and oxygen was burned in an excess of pure
oxygen to yield 0.8635 g of CO2 and 0.1767 g of H2O. What is the empirical formula of the compound?
A. CHO
B. C2H2O
C. C3H3O2
D. C6H3O2
14.
When 0.200 L of 0.015 M Pb(NO3)2 is mixed with 0.300 L of 0.050 M KI, the value of Q will be ________ and the
bright yellow precipitate, PbI2, _________ . (Ksp for PbI2 is 9.8 x 10-9).
A. Less than Ksp; will form
B. Greater than Ksp; will form
C. Less than Ksp; will not form
D. Greater than Ksp; will not form
15.
What effect will an increase in temperature have on the reaction below?
2SO3(g) ↔ 2SO2(g) + O2(g) ΔH° = +98.3 kJ per mole SO3
A. Shift the equilibrium to the right
B. Shift the equilibrium to the left
C. Will have no effect on the equilibrium
16.
In the rate law, Rate = k[NO]2[O2], the reaction is ___ order for NO, and ____ order for O 2, and _____ overall order.
A.
B.
C.
D.
Second; first; third
Second; zero; third
First; second; third
First; third; first
17.
How many grams of silver nitrate (AgNO3) are required to produce 44.0 g of aluminium nitrate (Al(NO 3)3)?
6AgNO3 + Al2(SO4)3 → 3Ag2SO4 + 2Al(NO3)3
A. 105.3 g
B. 132.0 g
C. 169.9 g
D. 213.0 g
18.
A 2.50 kg piece of copper metal is heated from 25°C to 225°C. How much heat, in kJ, is absorbed by the copper? The
specific heat capacity of copper is 0.384 J/g°C.
A. 124 kJ
B. 156 kJ
C. 192 kJ
D. 212 kJ
19.
2HF(g) ↔ H2(g) + F2(g)
Keq = 1.00 x 10-2
1.00 mol HF, 0.500 mol H2, and 0.750 mol F2 are mixed in an evacuated 5.00 L flask. In which direction will the
equilibrium shift to establish equilibrium?
A. the equilibrium shifts to the right
B. The equilibrium shifts to the left
C. The system is at equilibrium
20.
The Ksp of PbSO4(s) is 1.3 x 10-8. Calculate the solubility (in mol/L) of PbSO4(s) in a 0.10 M solution of Na2SO4.
A. 1.3 x 10-10
B. 4.5 x 10-6
C. 1.3 x 10-5
D. 1.3 x 10-7
21.
The graph shown is consistent with what type of reaction?
A. Zero order
B. First order
C. Second order
Third order
D.
22. The rate expression for a particular reaction is
Rate = k[P][Q]
Which of the units below is a possible unit for k?
A. mol–2 dm6 min–1
B. mol–1 dm3 min–1
C. mol dm3 min–1
D. mol–2 dm–6 min–1
23. The average bond enthalpies for O—O and O==O are 146 and 496 kJ mol–1 respectively.
What is the enthalpy change, in kJ, for the reaction below?
H—O—O—H(g) → H—O—H(g) + ½O==O(g)
A. – 102
B. + 102
C. + 350
D. + 394
24. What will happen to the volume of a fixed mass of gas when its pressure and temperature (in Kelvin) are
both doubled?
A. It will not change.
B. It will increase.
C. It will decrease.
D. The change cannot be predicted.
25. Lithium hydroxide reacts with carbon dioxide as follows.
2LiOH + CO2 → Li2 CO3 + H2O
What mass (in grams) of lithium hydroxide is needed to react with 11 g of carbon dioxide?
A. 6
B. 12
C. 24
D. 48
26. Excess magnesium was added to a beaker of aqueous hydrochloric acid on a balance. A graph of the mass
of the beaker and contents was plotted against time (line 1).
What change in the experiment could give line 2?
I.
The same mass of magnesium but in smaller pieces
II. The same volume of a more concentrated solution of hydrochloric acid
III. A lower temperature
A. I only
B. II only
C. III only
D. None of the above
27. When 40 joules of heat are added to a sample of solid H2O at –16.0°C the temperature increases to –8.0°C.
What is the mass of the solid H2O sample?
[Specific heat capacity of H2O(s) = 2.0 J g–1K–1]
A. 2.5 g
B. 5.0 g
C. 10 g
D. 160 g
28. The percentage by mass of the elements in a compound is
C = 72%, H = 12%, O = 16%.
What is the mole ratio of C:H in the empirical formula of this compound?
A. 1 : 1
B. 1 : 2
C. 1 : 6
D. 6 : 1
48.
According to the enthalpy level diagram below, what is the sign for ΔH and what term is used to refer to the
reaction?
ΔH
reaction
A.
B.
C.
D.
positive
negative
positive
negative
endothermic
exothermic
exothermic
endothermic
Free-response
1.
Write balanced symbol equations for the laboratory situations described below. In all cases, a reaction occurs. Assume
that solutions are aqueous unless otherwise indicated.
Example: A strip of magnesium is added to a solution of silver nitrate Mg + 2Ag+ → Mg2+ + 2Ag
a. Butanol is burned in air
b. Excess hydrochloric acid solution is added to a solution of potassium hydrogen carbonate
c. Calcium oxide powder is added to distilled water
d. Solid ammonium nitrate is heated to temperatures above 300°C
e. Solid lead (II) carbonate is added to 0.5 M sulfuric acid solution
f. A mixture of powdered iron (III) oxide and powdered aluminum is heated strongly
g. A 0.2 M barium nitrate solution is added to an alkaline 0.2 M potassium chromate solution
2. Consider the equations represented below.
a.
O3(g) + NO(g) → O2(g) + NO2(g)
Referring to the data in the table below, show that the standard enthalpy change, ΔH°, for the reaction at 25°C is 200 kJ.
O3(g)
NO(g)
NO2(g)
Standard enthalpy of
formation, ΔH°f, at 25°C
(kJ mol-1)
b.
c.
d.
90
33
Make a qualitative prediction about the magnitude of the standard entropy change, ΔS°, for the reaction at 25°C.
Justify your answer.
On the basis of your answers to parts a. and b., predict the sign of the standard free-energy change, ΔG°, for the
reaction at 25°C. Explain your reasoning.
Use the information in the table below to write the rate-law expression for the reaction, and explain how you
obtained your answer.
Experiment number
e.
143
Initial [O3] (mol L-1)
Initial [NO] (mol L-1)
Initial rate of formation
of NO2 (mol L-1 s-1)
1
0.0010
0.0010
x
2
0.0010
0.0020
2x
3
0.0020
0.0010
2x
4
0.0020
0.0020
4x
The following tree-step mechanism is proposed for the reaction. Identify the step that must be the slowest in order
for this mechanism to be consistent with the rate-law expression derived in part d. Explain
Step I:
O3 + NO → O + NO3
Step II:
O + O3
Step III:
NO3
+
→
NO
2O2
→
2NO2
3.
An equation for the decomposition of substance A is
2A → 2B + C
A graph showing the change in concentration of A against time as the reaction proceeds at a particular
temperature is shown below.
a.
b.
Define the term half-life of reaction.
Use the graph to measure values of half-life of reaction, starting from
time = zero
time = 1000 s
c.
Deduce the order of the reaction with respect to A, giving a reason for your choice, and write the rate
expression for the reaction.
d.
For a different reaction, between compounds D and E, the rate expression is
rate = k[D]2[E]
Calculate the value of k, including units, for the reaction when the concentrations of both D and E are
1.35×10–2 mol dm–3 and the reaction rate is 3.75×10–5 mol dm–3 min–1.
4.
A
B
C
a.
(
The diagram shows the distribution of energy for the molecules in a sample of gas at a given temperature, T1.
a. In the diagram Ea represents the activation energy for a reaction. Define this term.
b. On the diagram above draw another curve to show the energy distribution for the same gas at a
higher temperature. Label the curve T2.
c. With reference to your diagram, state and explain what happens to the rate of a reaction when the
temperature is increased.
6.
A certain line in the spectrum of atomic hydrogen is associated with the electron transition in the H atom from the sixth
energA rate study of the reaction represented below was conducted at 25°C. The data that were obtained are shown in the
table underneath.
2NO(g) + Br2(g) → 2NOBr(g)
a.
b.
c.
d.
Experiment
Initial [NO] (mol L-1)
Initial [Br2] (mol L-1)
Initial rate of formation
of NO2 (mol L-1 s-1)
1
0.0160
0.0120
3.24 x 10-4
2
0.0160
0.0240
6.38 x 10-4
3
0.0320
0.0060
6.42 x 10-4
Calculate the initial rate of disappearance of Br2(g) in experiment 1
Determine the order of the reaction with respect to each reactant, Br 2(g) and NO(g). In each case, explain your
reasoning.
For the reaction,
i.
Write the rate law that is consistent with the data, and
ii.
Calculate the value of the specific rate constant, k, and specify units
The following mechanism was proposed for the reaction:
Br2(g) + NO(g) → NOBr2(g)
slow
NOBr2(g) + NO(g) → 2NOBr(g)
fast
Explain whether this mechanism is supported by the rate expression. If not, suggest an alternative.
7.
Answer the following questions in terms of thermodynamics principles and concepts of kinetic molecular theory.
a. Consider the reaction represented below, which is spontaneous at 298 K.
CO2(g) + 2NH3(g) → CO(NH2)2(s) + H2O(l)
ΔH°298 = -134 kJ
i.
For the reaction, indicate whether the standard entropy change, ΔS° 298, is positive, or negative, or zero.
Justify your answer.
ii.
Which factor, the change in enthalpy, ΔH°298, or the change in entropy, ΔS°298, provides the principal
driving force for the reaction at 298 K? Explain.
iii.
For the reaction, how is the value of the standard free energy change, ΔG°, affected by an increase in
temperature? Explain.
b. Some reactions that are predicted by their sign of ΔG° to be spontaneous at room temperature do not proceed at a
measurable rate at room temperature.
i.
Account for this apparent contradiction.
ii.
A suitable catalyst increases the rate of such a reaction. What effect does the catalyst have on ΔG° for the
reaction? Explain.
11.
The graph below shows the volume of carbon dioxide gas produced against time when excess calcium
carbonate is added to x cm3 of 2.0 mol dm–3 hydrochloric acid.
a.
b.
Write a balanced equation for the reaction.
State and explain the change in the rate of reaction with time. Outline how you would determine the
rate of the reaction at a particular time.
c.
Sketch the above graph on an answer sheet. On the same graph, draw the curves you would expect if:
I.
the same volume (x cm3) of 1.0 mol dm–3 HCl is used.
II.
double the volume (2x cm3) of 1.0 mol dm–3 HCl is used.
Label the curves and explain your answer in each case.
12. a.
Draw a graph to show the distribution of energies in a sample of gas molecules. Label the
axes and label your curve T1. Using the same axes, draw a second curve to represent the
distribution of energies at a higher temperature. Label this curve T2.
b. State and explain, with reference to your graph, what happens to the rate of a reaction when the
temperature is increased.