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11.3 The Ideal Gas Law
POINT > Review the Gas Laws
POINT > Use KMT to explain how different gases
occupy the same volume
POINT > Show that equation coefficients can indicate
gas volumes
POINT > Define the Ideal Gas Law
POINT > Review the Gas Laws
Boyle’s Law:
P1V1  P2V2
Charles’ Law:
V1 V2

T1 T2
Combined Gas Law:
(Units MUST match and
temperature in Kelvin!)
P1V1 P2V2

T1
T2
POINT > Review the Gas Laws
A gas with a volume of 350. ml is collected at 15.0o C
and 120. kPa. If the temperature changes to 30.0o C,
what pressure would be required to put this gas in a
300. ml container?
120kPa  350ml P2  300ml

288K
303K
P2  147.3kPa
WB CHECK:
A balloon has a volume of 500. ml at a temperature of
22.0oC and a pressure of 755 mmHg. If the balloon is
cooled to 0.00o C and a pressure of 145 mmHg, what
is its new volume?
755mmHg  500ml 145mmHg  V2

295K
273K

2410
ml
V2
POINT > Use KMT to explain how different gases
occupy the same volume
KMT tells us that gas particles, regardless of size,
do not interact with each other
Gay-Lussac noticed a volume relationship:
2 liters of H2 gas combined with 1 liter of O2 gas to
form 2 liters of H2O vapor...
POINT > Use KMT to explain how different gases
occupy the same volume
Here is the balanced equation:
2 H2 + O2  2 H2O
The volume ratios of reactant and product gases
were always small whole numbers (Gay-Lussac)
Avogadro: At the same temperature and pressure, a
defined volume of any gas has the same number of
particles
(At STP 1 mole of gas = 22.4L)
POINT > Show that equation coefficients can
indicate gas volumes
If the reactants and products are gases, then the
equation coefficients can indicate moles or volumes
(Why?)
One mole of any gas has the same number of
particles (Avagadro’s number)
The same number of particles of any gas occupy the
same volume
Stoichiometry can extend to gas volumes, as well as
moles
WB CHECK:
2 C4H10 + 13 O2  8CO2 + 10 H2O
If 4.00 L of butane are combusted, how many L of
water vapor could be produced?
If 36.0 L of CO2 is produced during the above
reaction, how much O2 was used?
58.5 L
POINT > Define the Ideal Gas Law
KMT tells us that pressure, temperature, and
volume will all be affected by the number of
gas particles
This leads to the Ideal Gas Law:
PV = nRT
POINT > Define the Ideal Gas Law
PV = nRT
n = number of moles
R = .0821 the gas constant if using atm, liters, and
Kelvin as units
If not using these units, convert to them or use a
different R (Figure 3.4 p. 364)
WB CHECK:
PV = nRT
Given 3 of the values, calculate the unknown
quantity:
How many moles of gas are contained in 890.0 mL at
21.0 °C and 750.0 mm Hg pressure?
~ 0.036 moles
Hint: If the problem involves # of moles or mass, you
must use the Ideal Gas Law to solve!
WB CHECK:
A 50.0L container of methane at STP contains
how many moles of methane?
50.0L x 1 mole = 2.23 mol methane
22.4 L
WB CHECK:
At STP, what volume would 5.50 moles of water
vapor occupy?
5.50mol x 22.4L
1 mol
= 123L water vapor
Homework:
Read pages 358-365
7 Practice problems 358-365
FA #1-6 Page 365