1. Ch.14: Gas Laws
Part 1

2. Pressure of the Atmosphere
Called “atmospheric pressure,” or the force exerted upon us by the atmosphere above.
A measure of the weight of the atmosphere pressing down upon us.
Measured using a barometer - A device that can weigh the atmosphere above us.

3. A Mercury Barometer

4. Common Units of Pressure
Unit Atmospheric Pressure Scientific Field
pascal (Pa); x 105 Pa SI unit; physics,
kilopascal(kPa) kPa Chemistry
atmosphere (atm) atm* Chemistry
millimeters of mercury mmHg* Chemistry, medicine,
( mm Hg ) biology
torr torr* Chemistry
pounds per square inch lb/in Engineering
( psi or lb/in2 )
bar bar Meteorology, chemistry,
physics

5. Problem 1: Converting Units of Pressure
Problem: A chemist collects a sample of Carbon dioxide from the
decomposition of limestone (CaCO3), the height of the mercury is
341.6 mm Hg. Calculate the CO2 pressure in
torr, atmospheres, and kilopascals.
Plan: The pressure is in mmHg, so we use the conversion factors from
The preceding table to find the pressure in the other units.
Solution:
converting from mm Hg to torr:
(a) PCO2 (torr) =
converting from torr to atm:
(b) PCO2( atm) =
converting from atm to kPa:
(c) PCO2(kPa) =

6. Boyle’s Law : P - V Relationship
Pressure is inversely proportional to volume at fixed temperature and fixed amount:
P1V1 = P2V2
Where:
P is the pressure exerted by the sample on the surroundings.
V is the volume occupied by the sample in Liters

7. Problem 2: Applying Boyles Law
Problem: A gas sample at a pressure of 1.23 atm has a volume of
15.8 cm3, what will be the volume if the pressure is increased to
3.16 atm?
Plan: We begin by converting the volume that is in cm3 to mL and then
to liters, then we do the pressure change to obtain the final volume.
Solution:
P1 = 1.23 atm P2 = 3.16 atm
V1 = 15.8 cm V2 = unknown
T and n remain constant
V1 =
V2 =

8. Charles’s Law : V - T Relationship
Volume is directly proportional to temperature at fixed pressure and fixed amount:
V1 = V2
T T2
Where:
V is the volume occupied by the sample in Liters.
T is the temperature in degrees Kelvin.
Kelvin is the SI unit for temperature. To convert celsius to Kelvin, simply add 273.
K = Co + 273

9. Problem 3: Charles Law
A sample of carbon monoxide, a poisonous gas, occupies 3.20 L at 125 oC. Calculate the temperature (oC) at which the gas will occupy 1.54 L if the pressure remains constant.
V1 = T1 =
V2 = T2 =
T2 =
T2 = oC =

10. Gay-Lussac’s Law How are temperature and pressure of a gas related?
Pressure of a gas varies directly with the temperature.
P1 = P2
T T2
Where P = pressure, T = temperature in Kelvin

11. Problem 4: Gay-Lussac’s Law
Problem: A copper tank is compressed to a pressure of 4.28 atm at a
temperature of 350 K. What will be the pressure if the temperature is
raised to 95.6 oC?
Solution:
T1 =
T2 =
P1 =

12. Combined Gas Law
Boyle’s Law, Charles’s Law, and Gay-Lussac’s Law can all be combined together to show the relationship of pressure, volume, and temperature of a specific amount of a gas.
P1V1 = P2V2
T T2

14. Avogadro’s Law : V - n Relationship
Equal volumes of gases at the same temperature and pressure contain the same number of particles.
Standard Temperature and Pressure (STP)
A set of Standard conditions have been chosen to make it easier to
understand the gas laws, and gas behavior.
Standard Temperature = 00 C = K
Standard Pressure = 1 atmosphere = 760 mm Mercury
At these “standard” conditions 1.0 mole of a gas will
occupy a “standard molar volume”.
Standard Molar Volume = Liters = 22.4 L