Review Packet Unit VI
Chapter 13 & 14 Gas Laws
1.
2.
3.
4.
The physical behavior of a gas depends on its volume, temperature, ______Pressure_________.
A gas has random motion because it has ____Kinetic____ energy.
Atmospheric pressure ______decreases__________ with an increase in elevation.
If equal volumes of gases are at the same temperature and pressure, the volumes must contain the ___same__
number of particles [could be a mole (6.02 x 1023).
1.
A rigid container of O2 has a pressure of 3.5 atm at a temperature of 713 K.
What is the pressure at 1426 K.
Common sense: The temperature (Kelvin (K.E.) doubles the pressure will double. Ans: 7.0 atm.
P2 = P1 T2 .
P2 = 3.5 atm x 1426 K .
P2 = 7.0 atm
T1
713 K
2.
How many nitrogen molecules are in 5.62 L of nitrogen gas at STP?
5.62 L x
3.
1 mol N2
22.4 L N2
x
6.02 x 1023 molecules N2
1 mol N2
=
1.51 x 1023 molecules N2
Which has the greater pressure? Show all conversions to verify your answer.
Must all be in the same unit to compare and select.
1.79 atm
952 mmHg x
1.00 atm = 1.25 atm
760 mm Hg
195.5 kPa
x
1.00 atm
= 1.93 atm Greatest Pressure
101.3 kPa
4.
Charles' (Pressure is constant, so the graph will
show volume versus temperature, where
temperature is the independent variable.)
Boyle's (Temperature is constant, so the graph
will show pressure versus volume, where
volume is the independent variable.)
Gay-Lussac's (Volume is constant, so the graph
will show pressure versus temperature, where
temperature is the independent variable.)
5.
A sample of gas under a pressure of 855 kPa has a volume of 3.50 mL. The pressure is increased to 995 kPa. What
volume will the gas occupy at the new pressure, assuming that the temperature is constant?
V2 =
V1 P1
P2
V2 =
3.50 mL x 855 kPa
995 kPa
V2 = 3.01 mL = 0.00301 L
6.
A 212 L sample of a gas exerts a pressure of 316.6 mmHg when its temperature is 38oC. What volume would it
occupy at 33.3 kPa and 34oC?
First convert 316.6 mmHg to kPa (or you could convert 33.3 kPa to mmHg, you would get the same answer).
316.6mmHg x 101.3 kPa = 42.2 kPa
760 mmHg
V2 =
P1 V1 T2
P2 T1
7.
A gas with a volume of 345 mL at 47oC is heated until its volume is 894 mL. What is its new temperature?
T2 = V2
T1
V1
V2 = 42.2 kPa x 212 L x 307 K
33.3 kPa 311 K
T2 = 894 mL x 320 K =
345 mL
V2 = 265 L
T2 = 829 K (sig figs)
8.
A 5.00 L air sample has a pressure of 107 kPa at a temperature of –50oC. If the temperature is raised to 102oC
and the volume expands to 7.00 L, what will the new pressure be?
P2 =
P1 V1 T2
V2 T1
P2 = 107 kPa x 5.00 L x 375 K
7.00 L x 223 K
P2 = 128.52 = 129 kPa
9.
P =
If 0.0025 moles of Hydrogen gas is formed by bubbling it up through water. The gases occupy a volume of 45.55
mL at 20.0oC. What is the total pressure of all of the gases and the pressure of the dry hydrogen gas if the PH2O
is 2.33 kPa?
n R T
V
Ptotal = PH2
PH2 = Ptotal
10.
+
-
P = 0.0025 mol x 8.31 kPa L x 293 K
0.04555 L
K mol
PH2O
PH2O
134 kPa - 2.33 kPa =
Ptotal = 134 kPa
132 kPa (with sig figs)
What is the total pressure of a mixture of nitrogen, oxygen, and carbon monoxide gases? The N2 has a pressure of
125,0 kPa, the O2 has a pressure of 538.5 mmHg, and the CO has a pressure of 0.732 atmospheres.
All have to be the same unit, I choose to change them all to kPa
538.5 mmHg x 101.3 kPa
= 71.78 kPa
0.732 atm x 101.3 kPa
760 mmHg
1 atm
Add all the pressures: 125.0 kPa + 71.78 kPa + 74.2 kPa = 271 kPa
12.
= 74.2 kPa
What distinguishes effusion from diffusion? How are these processes similar?
Both are processes where particles move from an area of high concentration to all areas of lower
concentration. Diffusion is in all directions spreading out, whereas effusion is the movement of a
gas through a small opening and more directional. The lab/demo was more of an example of
effusion, although once given any space gases move out in all directions.
13.
Calculate the ratio of the velocity of He atoms to the velocity of fluorine molecules at the same temperature.
He mass of 4.0 g/mol and F2 has a mass of 38.0 g/mol so He will travel faster and further.
Rate He = √Mass F2 38.0 g/mol Rate He = 6.16 = 3.08 so while He goes3.08 the F2 only goes 1.0
Rate F2
√Mass He 4.0 g/mol
Rate F2
2.0
1.0
14.
A certain gas effuses four times as fast as oxygen (O2) gas. What is the molar mass of the gas?
While the Gas X goes 4 O2 only goes 1, this is the rate comparison,
so the Gas X must be lower in mass than the O2.
O2 has a mass of 32.0 g/mol, so what is the mass of Gas X?
Rate X (4) = √Mass O2 32.0 g/mol
Rate O2 (1) √Mass X ??? g/mol
Have to square
both sides
Rate 16 = 32.0g/mol
Rate 1
??
Mass X = 32.0g/mol (1) =
16.0
2.0 g/mol Hydrogen gas
H2
16.
Magnesium burns in air to produce magnesium oxide, MgO, and magnesium nitride, Mg 3N2. Magnesium nitride reacts
with water to give ammonia. Mg3N2
+ 6 H2O (l)

3 Mg(OH)2 (s) + 2 NH3 (g)
4.56 g
??? moles to get to Liters
What volume of ammonia gas at 24oC and 753 mmHg will be produced from 4.56 g of magnesium nitride?
Stoichiometry to get to moles of NH3, then use the moles (n) in the Ideal Gas Law Equation to get
to Liters at non STP conditions.
4.56 g Mg3N2 x
1 mol Mg3N2
x
2 mol NH3 =
0.0900 mol NH3 = n
100.9 g Mg3N2
1 mol Mg3N2
T = 24oC + 273 = 297 K
P = 753 mmHg x 101.3 kPa =100.37 kPa
760 mmHg
P V = n R T
V = n R T . = 0.0900 mol x 8.31 kPa L
P
100.37 kPa
K mol
x 297 K = 2.21 L
17.
How many grams of chlorine (Cl2) exist in a container that has a volume of 2.00 L, and pressure of 19.2 psi and is at
a temperature of 25.0oC?
First convert psi to kPa (or atm) 19.2 psi x 101.3 kPa = 132.0 kPa
14.7 psi
Solve for moles (n) and them use molar mass to change to grams.
n
18.
= P V
R T
132.0 kPa x 2.00 L =
8.31 kPa L x 298 K
K mol
0.11 mol Cl2 x 71.0 g Cl2 = 7.57 g Cl2
1 mol Cl2
At standard conditions, it was found that 1.00 L of a gas weighed 0.760 g. What is the compounds molecular
(molar) mass?
Need to be in the unit of g/mol and the problems mentions STP so
0.760 g x 22.4 L = 17.02 g/mol
1.00 L
1 mol gas
19.
Sodium hydrogen carbonate is also known as baking soda. When this compound is heated, it decomposes to sodium
carbonate, carbon dioxide, and water vapor. Write a balanced chemical equation for this reaction.
2 NaHCO3

35.4 g reacts
Na2CO3
+ CO2
+ H 2O
solve for moles of gas from the CO2 and H2O
35.4 g NaHCO3 x 1 mol NaHCO3 x 1 mol CO2
= 0.21 mol CO2 use this to solve 2nd part
84.0 g NaHCO3
2 mol NaHCO3
What volume (in liters) of carbon dioxide gas at 91oC and 756 mmHg will be produced from 35.4 g of sodium hydrogen
carbonate?
V = n R
T
V = 0.21 mol x 8.31 kPa L
100.77 kPa
K mol
x 364 K
=
6.30 L
Multiple Choice Practice
1.
A gas occupies a volume of 1.50 L at 700 mmHg and 200°C. Which mathematical expression gives the correct
volume at 400 mmHg and 100°C? V2 = P 1 V1 T2 Change temp to Kelvin
P2 T1
1.50 x
d.
2.
For a gas, which two variables are DIRECTLY proportional to each other (if all other conditions remain
constant)?
3.
700 373

400 473
1.
2.
3.
P and V
P and n
P and T
(INVERSE)
e.
2 and 3 only
Which of the following gases has the greatest density at 2.5 atm and 25°C? (Calculate Molar Mass)
a.
d.
N2O (44.0 g/mol)
C3H8 (44 g/mol)
b.
e.
F2 (38.0 g./mol)
NF3 (71.0 g/mol)
c.
HNF2 (53.0 g/mol)
4.
A given mass of gas in a rigid container is heated from 100 to 500°C. Which of the following responses best
describes what will happen to the pressure of the gas?
The pressure will go up but remember that you have to change the oC to Kelvin (K) so it goes from
373 K to 773 K by a factor of 2.07 so D.
a.
b.
c.
d.
e.
5.
The
The
The
The
The
pressure will remain the same.
pressure will decrease by a factor of five.
pressure will increase by a factor of five.
pressure will increase by a factor less than five.
pressure will increase by a factor greater than five.
Equal volumes (1.0 L) of ozone, O3,
(Mass 48.0 g/mol and has 3 atoms) and methanethiol, CH3SH, (Mass
48.0 g/mol and has 6 atoms) under the same conditions(can be STP) have equal
6.
YES
NO
3.
masses.
YES
e.
1 and 3 only
None of these is true.
For the following reactions consider the reactants, after the reaction has finished (only products exist) and the
substances return to the same initial temperature, which system will have an increase in pressure? More Moles?
a.
b.
c.
d.
e.
8.
numbers of molecules.
numbers of atoms.
Three 1.0-L flasks are filled with H2 (Mass 2.0 g/mol), O2 (32.0 g/mol), and Ne (20.2 g/mol), respectively, at
STP. Which of the following statements is TRUE?
a.
All the flasks have the same number of gas molecules.
YES
b.
The velocity of the gas molecules is the same in all the flasks.
NO depends on Mass
c.
The densities of all the gases are the same.
NO depends on Mass
d.
There are twice as many O2 and H2 molecules as Ne atoms.
NO just twice as many atoms
e.
7.
1.
2.

 2 ClF3(g)
4 NH3(g) + 5 O2(g) 
 4 NO(g) + 6 H2O(g)
 2 NO2(g)
2 NO(g) + O2(g) 
C2H6O(l) + 3 O2(g) 
 2 CO2(g) + 3 H2O(l)
 CO2(g)
C(s) + O2(g) 
Cl2(g) + 3 F2(g)
2 mole of Gas
10 moles of Gas
2 moles of Gas
2 moles of Gas, water a liquid
1 mole of Gas
Which of the following gases will have the slowest rate of diffusion (assume they are all at the same
temperature): The one with the largest mass
a.
d.
CF4. (88 g/mol)
Ne. (20.2 g/mol)
b.
e.
F2. (38.0 g/mol)
SO3 (80.0 g/mol)
c.
H2. (2.0 g/mol)