Slide 1

Gas Laws
Robert Boyle

Jacques Charles

Amadeo Avogadro

Joseph Louis Gay-Lussac


Slide 2

Boyle’s Law
Pressure is inversely proportional to
volume when temperature is held
constant.

P1V1  P2V 2


Slide 3

1 A diver’s lungs hold about 20.0 L of
air underwater at a pressure of 875
mm Hg. Assuming he holds his breath
and his lungs don’t burst, what will be
the volume of air in his lungs at
standard pressure on the water’s
surface.

A. 20.0 L
B. 30.2L
C. 23.0 L
D. 87.5 L


Slide 4

Charles’s Law
The volume of a gas is directly proportional
to temperature, and extrapolates to zero at
zero Kelvin.
(P = constant)

V1
T1



V2
T2

Temperature MUST be in KELVINS!


Slide 5

2. A shampoo bottle contains 443 mL of
air at 65C. What is its volume when it
cools to 22C?

A. 386.6 ml
B. 4.3 L
C. 350.0 ml
D. 700.4 ml


Slide 6

Gay Lussac’s Law
The pressure and temperature of a gas are
directly related, provided that the volume
remains constant.

P1
T1



P2
T2

Temperature MUST be in KELVINS!


Slide 7

3. When a canning jar is sealed at 100C
the pressure inside is 101.3 kPa. What
is the pressure inside the jar when it
cools to room temperature, about 21C?
A. 100 atm
B. 200 Kps
C. 84.0 kpa
D. 79.8 Kpa


Slide 8

The Combined Gas Law
The combined gas law expresses the
relationship between pressure, volume and
temperature of a fixed amount of gas.

P1V1
T1



P2V 2
T2


Slide 9

4. A sample of propane has a volume of
250.0 L at 125 kPa and 38C. What
volume will this sample have at 100.0 kPa
and 95C?

A. 370 . 0 L
B. 100 . 0 L
C. 250.3 L


Slide 10

Ideal Gas Law

PV = nRT

 P = pressure in atm
 V = volume in liters
 n = moles
 R = proportionality constant
= 0.08206 L atm/ mol·K
 T = temperature in Kelvins

Holds closely at P < 1 atm


Slide 11

5. A balloon is filled with helium to a
volume of 12.5 liters at 25C and 1.01
atm. How many grams of helium are in
the balloon?

A. 2.07 . g
B. .52 g
C. 4.04 g


Slide 12

Gas Density

… so at STP…


Slide 13

Density and the Ideal Gas Law
Combining the formula for density with the
Ideal Gas law, substituting and rearranging
algebraically:
M = Molar Mass
P = Pressure
R = Gas Constant

T = Temperature in Kelvins


Slide 14

Gas Stoichiometry #1
If reactants and products are at the same
conditions of temperature and pressure,
then mole ratios of gases are also volume
ratios.
3 H2(g)

+

N2(g)



2NH3(g)

3 moles H2

+ 1 mole N2



2 moles NH3

3 liters H2

+ 1 liter N2



2 liters NH3


Slide 15

Gas Stoichiometry #2
How many liters of ammonia can be
produced when 12 liters of hydrogen react
with an excess of nitrogen?

3 H2(g) + N2(g)
12 L H2



2 L NH3
3 L H2

2NH3(g)
=

8.0

L NH3


Slide 16

Gas Stoichiometry #3
How many liters of oxygen gas, at STP, can
be collected from the complete decomposition
of 50.0 grams of potassium chlorate?
2 KClO3(s)  2 KCl(s) + 3 O2(g)

50.0 g KClO3

1 mol KClO3
122.55 g KClO3

3 mol O2

22.4 L O2

2 mol KClO3

1 mol O2

= 13.7 L O2


Slide 17

Gas Stoichiometry #4

How many liters of oxygen gas, at 37.0C
and 0.930 atmospheres, can be collected
from the complete decomposition of 50.0
grams of potassium chlorate?
2 KClO3(s)  2 KCl(s) + 3 O2(g)
50.0 g KClO3

1 mol KClO3

3 mol O2

122.55 g KClO3

V

nRT
P



(0.612 mol)(0.082

2 mol KClO3
1

L  atm

mol  K
0.930 atm

)(310 K)

=

0.612
mol O2

= 16.7 L


Slide 18

Dalton’s Law of Partial Pressures
For a mixture of gases in a
container,

PTotal = P1 + P2 + P3 + . . .
This is particularly useful in calculating
the pressure of gases collected over
water.


Slide 19

Partial Pressures
6) A vessel contained N2, Ar, He, and Ne.
The total pressure in the vessel was 987
torr. The partial pressures of nitrogen,
argon, and helium were 44.0, 486, and 218
torr, respectively. The partial pressure of
neon in the vessel was __________ torr.
A) 42.4
B) 521
C) 19.4
D) 239