AP Chemistry
Review, Chapters 5, and 6 12/07
1.
Consider three 1-L flasks at STP. Flask A contains NH3 gas, flask B contains NO2 gas, and flask C contains N2
gas.
In which flask do the molecules have the highest average velocity?
a. flask A
b. flask B
c. flask C
d. all are the same
e. none
In which flask are the molecules least polar and therefore most ideal in behavior?
a. flask A
b. flask B
c. flask C
d. all are the same
e. none
2.
A gas sample is held at constant pressure. The gas occupies 3.62 L of volume when the temperature is 21.6°C.
Determine the temperature at which the volume of the gas is 3.45 L.
T2 
3.
4.
5.
V2  T1 3.45L  294.6 K

 280.8 K
V1
3.62 L
An automobile tire is filled with air at a pressure of 30 lb/in2 at 25°C. A cold front moves through and the
temperature drops to 5°C. Assuming no change in volume, what is the new tire pressure?
a. 6.0 lb/in2
b.
28 lb/in2
c.
32 lb/in2
d.
20 lb/in2
e.
4.0 lb/in2
Which conditions of P, T, and n, respectively, are most ideal?
a. high P, high T, high n
b.
low P, low T, low n
c.
high P, low T, high n
d.
low P, high T, high n
e.
low P, high T, low n
A plastic bag is weighed and then filled successively with gas X. The following data are gathered:
Temperature: 0.0°C (273 K)
Pressure: 1.00 atmosphere
Mass of empty bag: 20.77 g
Mass of bag filled with gas X: 24.97 g
Volume of bag: 1.12 liter
Molar volume at STP: 22.4 liters
What is the molar mass of gas X?
6.
Molar Mass 
 4.20 g    0.0821 L  atm  mol 1  K 1    273 K 
 84 g/mol
1.00 atm   1.12 L 
When 0.72 g of a liquid is vaporized at 110°C and 0.967 atm, the gas occupies a volume of 0.559 L. The
empirical formula of the gas is CH2. What is the molecular formula of the gas?
 0.72 g    0.0821 L  atm  mol 1  K 1    383 K 
Molar Mass 
 42 g/mol
 0.967 atm    0.559 L 
= 3 ∙ CH2
7.
= C3H6
Gaseous C2H4 (acetylene) reacts with O2 according to the following equation:
C2 H4( g )  3O2( g )  2CO2( g )  2H2O( g )
0.70 mol
2.1 mol
What volume of oxygen at STP is needed to react with 40.0 grams of C2H4?
 2.1 mol 
8.
22.4 L

mol
47 mol O2
How many grams of F2 must react with an excess of NaCl in the following reaction to release 800 kJ of energy?
2NaCl + F2  2NaF + Cl2
9.
a.
47.5
b.
95.0
c.
40.0
d.
125
e.
190
In the following reaction, 2C3H8  C6H6 + 5H2,
H = −320 kJ
H = 698 kJ. How many moles of hydrogen gas are released
if 4188 kJ of heat are absorbed during a reaction?
a.
28
b.
1.1
c.
6
d.
5
e.
30
10. The Law of Dulong and Petit states: (atomic weight) x (specific heat) = 25.9 J/mol K. The specific heat of an
element is found to be 0.646 J/g °C. What element is it?
a. Li
b.
Sn
c.
Ca
d.
S
e.
U
11. How much energy in joules is required to raise the temperature of 1 mole of sulfur (S) from 100 to 500°C? The
specific heat for sulfur is 0.705 J/g °C.
a.
280
b.
1.28 x 104
c.
9.04 x 103
d.
22.6
e.
567
12. A 1000 g sample of lead shot, at 300°C, is dropped into 100 g of water at a temperature of 5.6°C. The specific
heats of lead and water are 0.129 and 4.184 J/g °C,respectively. What is the final temperature of the mixture, in
degrees Celsius? To solve this remember that the heat lost by the lead has to equal the heat gained by the water
 mPb  cPb  tPb  mH O  cH O  tH O  and they reach the same final temperature.
2
2
2
mH 2O  cH 2O
t Pb

 3.24
t H 2O
mPb  cPb
t H 2O  69.4
75oC
t Pb  t H 2O  294.4
t final  5.6  69.4 
13. A 2.00 g sample of methane, CH4, is combusted in a calorimeter. The calorimeter and water combined have a
heat capacity of 43.50 kJ/K. The observed temperature rise is 1.74°C. Calculate the heat of combustion of
methane in kJ/mol. The products of the reaction are water and carbon dioxide.
CH4( g )  2O2( g )  CO2( g )  2H2O( g )
q  43.50 kJ
14. The
K
1.74o C 
75.69 kJ
 605.5 kJ/mol
2.00 g
H° of formation values for water vapor and liquid water are −241.82 and −285.83 kJ/mol, respectively.
Calculate the
H° of vaporization for water in kJ/mol.
H 2  O2  H 2O g 
H  241 kJ
H 2O l   H 2  O2
H  285.83 kJ
Hvap = 44.83 kJ
15. The compound silane is highly combustible and creates a fire hazard. The combustion reaction is: SiH 4(g) +
2O2(g)  SiO2(s) + 2H2O(g). Calculate
H° in kJ for this reaction using the following information:
Si(s) + 2H2(g)  SiH4(g)
H° = 34 kJ/mol
Si(s) + O2(g)  SiO2(s)
H° = −911 kJ/mol
H2(g) + ½O2(g)  H2O(g)
H° = −242 kJ/mol
SiH 4  Si s   2 H 2 g 
Si s   O2  SiO2
H  34 kJ
2 H 2  O2  H 2O
H  484
H  911
H = 1429 kJ
16. Calcium oxide, displaying basic properties, and sulfur trioxide, displaying acidic properties, should react in a
neutralization reaction as follows: CaO(s) + SO3(g)  CaSO4(s). Calculate the heat of reaction in kJ for this
reaction.
H° of formation values for CaO, SO3, and CaSO4 are −152, −396, and −1434 kJ/mol, respectively.
Hreaction  1434kJ   152  396  886 kJ