The Gas Laws
Boyle’s Law: Pressure and Volume
• If the temperature is constant, as the pressure
of a gas increases, the volume decreases.
• In turn, as the pressure decreases, the volume
increases.
Boyle’s Law: Pressure and Volume
• Boyle’s law states that for a given mass of gas
at constant temperature, the volume of the
gas varies inversely with pressure.
• P1 x V1 = P2 x V2
• P = pressure
• V = volume
Using Boyle’s Law
• A balloon contains 30L of helium gas at 103
kPa. What is the volume of the helium when
the balloon rises to an altitude where the
pressure is only 25 kPa?
• Step 1: use Boyle’s law: P1 x V1 = P2 x V2
Using Boyle’s Law
• Step 2: set up equation to solve for V2
o V2 = (V1 x P1) / P2
• Step 3: plug and chug
o V2 = (30L x 103 kPa) / 25 kPa
o V2 = 124 L
Using Boyle’s Law Practice
• 1. Nitrous oxide (N2O) is used as an anesthetic.
The pressure on 2.5 L of N2O changes from
105 kPa to 40.5 kPa. If the temperature does
not change, what will the new volume be?
Using Boyle’s Law Practice
• 2. A gas with a volume of 4 L at a pressure of
205 kPa is allowed to expand to a volume of
12 L. What is the pressure in the container if
the temperature remains constant?
Charles’s Law: Temperature and
Volume
• As the temperature of an enclosed gas
increases, the volume increases, if the
pressure is constant.
Charles’s Law: Temperature and
Volume
• Charles’s law states that the volume of a fixed
mass of gas is directly proportional to its
Kelvin temperature if the pressure is kept
constant.
• V1/T1 = V2/T2
Using Charles’s Law
• A balloon inflated in a room at 24 °C has a
volume of 4 L. The balloon is then heated to a
temperature of 58 °C. What is the new volume
if the pressure remains constant?
• Step 1: Turn Celsius into Kelvin K = C + 273
o 24 + 273 = 297 K for T1
o 58 + 273 = 331 K for T2
Using Charles’s Law
• Step 2: rearrange Charles’s law to isolate V2
o V2 = (V1 x T2) / T1
o Step 3: plug and chug
o V2 = (4L x 331K) / 297K = 4.46 L
Using Charles’s Law Practice
• 3. If a sample of gas occupies 6.8 L at 325°C,
what will its volume be at 25°C if the pressure
does not change?
Using Charles’s Law Practice
• 4. Exactly 5L of air at -50 °C is warmed to 100
°C. What is the new volume if the pressure
remains constant?
Gay-Lussac’s Law: Pressure and
Temperature
• As the temperature of an enclosed gas
increases, the pressure increases, if the
volume is constant.
Gay-Lussac’s Law: Pressure and
Temperature
• Gay-Lussac’s law states that the pressure of a
gas is directly proportional to the Kelvin
temperature if the volume remains constant.
• P1/T1 = P2/T2
Using Gay-Lussac’s Law
• The gas in a used aerosol can is at a pressure
of 103kPac at 25°C. If the can is thrown onto a
fire, what will the pressure be when the
temperature reaches 928°C?
• Step 1: turn celsius into kelvin
o 25 + 273 = 298 K
o 928 + 273 = 1201 K
Using Gay-Lussac’s Law
• Step 2: Use Gay-Lussac’s law and isolate P2
o P2 = (P1 x T2) / T1
o Step 3: Plug and chug
o P2 = (103 kPa x 1201 K) / 298 K = 415 kPa
Using Gay-Lussac’s Law Practice
• 5. The pressure in a car tire is 198 kPa at 27°C.
After a long drive, the pressure is 225 kPa.
What is the temperature of the air in the tire?
Using Gay-Lussac’s Law Practice
• 6. a sample of nitrogen gas has a pressure of
6.58 kPa at 539 K. If the volume does not
change, what will the pressure be at 211 K?
The Combined Gas Law
• The combined gas law describes the
relationship among the pressure,
temperature, and volume of an enclosed gas.
The Combined Gas Law
• The combined gas law allows you to do
calculations for situations in which only the
amount of gas is constant.
• P1 x (V1/T1) = P2 x (V2/T2)
Using The Combined Gas Law
• The volume of a gas filled balloon is 30L at 313
K and 153 kPa pressure. What would the
volume be at standard temperature and
pressure (STP)?
• Step 1: Realize that T2 = 273K and P2 = 101.3
kPa because they are at STP.
Using The Combined Gas Law
• Step 2: Rearrange the combined gas law to
isolate V2:
o V2 = (V1 x P1 x T2) / (P2 x T1)
• Step 3: Plug and Chug
o V2 = (30L x 153kPa x 273K) / (101.3kPa x 313K)
o V2 = 39.5 L
Combined Gas Law Practice
• 7. A gas at 155 kPa and 25°C has an initial
volume of 1L. The pressure of the gas
increases to 605 kPa as the temperature is
raised to 125°C. What is the new volume?
Combined Gas Law Practice
• 8. A 5L air sample has a pressure of 107kPa at
a temperature of 250°C. If the temperature is
raised to 102°C and the volume expands to 7L,
what will the new pressure be?