Unit 1 Gases
The Nature of Gases
Objectives:
1. Describe the assumption of the kinetic theory as it
applies to gases.
2. Interpret gas pressure in terms of kinetic theory
3. Define the relationship between Kelvin temperature
and average kinetic energy.
4. Explain why gases are easier to compress than solids
or liquids.
5. Describe the 3 factors that affect gas pressure.
 Properties of Gases
 take the shape of their container
 low density
 Compressible
 Mixtures are
homogeneous
 Fluids (flow)
 Gas pressure
 Results from collisions of gas particles with an object.
 In empty space where there are no particles, there is no
pressure and is called a vacuum.
 Atmospheric pressure (air pressure): due to atoms and
molecules in air.
 Barometer: used to
measure atmospheric
pressure.
 Units for measuring pressure:



Pascal (Pa)
Standard atmosphere (atm)
Millimeters of mercury (mmHg)
1 atm = 760 mmHg = 101.3 kPa
 1kpa = 1000 pa
 Standard pressure: 1 atm

 Factors affecting gas pressure
 Amount of gas
 Volume
 Temperature

Standard temperature : 0C (273K)
 Converting between units of pressure
A pressure gauge records a pressure of 450 kPa.
What is the measurement expressed in atmospheres
and millimeters of mercury?
For converting to atm:
450 kpa x 1 atm = 4.4 atm
1013.kPa
For converting to mmHg:
1.
450kPa x 760 mmHg = 3.4 x 103 mmHg
101.3 kPa
2. What pressure in kilopascals and in atmospheres,
does a gas exert at 385 mmHg?
51.3 kPa, 0.507 atm
3. The pressure on the top of Mount Everest is 33.7 kPa.
Is that pressure greater or less than 0.25atm?
33.7 kPa is greater than 0.25 atm
 Reaction_to_Air_Pressure_Below_Sea_Level.asf
 Classwork:
Read pages 103-105
Do problems 1,4,5,6
Gas Laws
 Objectives
Describe the relationships among the temperature,
pressure, and volume of a gas
2. Use the gas laws to solve problems
1.
Boyle’s Law : Pressure and Volume
 States that for a given mass of gas at constant
temperature, the volume of a gas varies inversely with
pressure.
 If pressure increases, volume decreases; if pressure
decreases, volume increases.
 Volume could be in liters (L),
mL, cm3, dm3 ,m3) 1L=1000 mL
1 cm3= 1 mL
 P1 x V1 = P2 x V2
P: pressure
V: volume
1: initial condition
2: final condition
YouTube - Self Inflating a Balloon
Marshmallow Man In A Vacuum (Family & Education:
Cool Experiments)
 Using Boyle’s Law
1.
A balloon with 30.0L of helium at 103kPa rises to an
altitude where the pressure is only 25.0kPa. What is
the volume of the helium (at constant temperature)?
P1 x V1 = P 2 x V2
2. A gas with a volume of 4.00L at a pressure of 205 kPa is
allowed to expand to a volume of 12.0L. What is the
pressure of the container now (at constant
temperature)?
P1 x V1 = P 2 x V2
 Classwork: pg 121 #1 (a-c), 2, 3, 4
Charles’s Law: Temperature and Volume
 States that the temperature of an enclosed gas varies
directly with the volume at constant pressure.
 As temperature increases, volume increases.
V1 = V2
T1 T2
V1: initial volume
V2: final volume
T1: initial temperature
T2: final temperature
Temperature has to be in Kelvin scale.
K =C + 273
Volume and Temperature
As a gas is heated, it expands.
This causes the density of the
gas to decrease.
YouTube - Balloon in liquid
nitrogen
 Using Charles’s Law
1.
A balloon inflated in a room at 24C has a volume of
4.00L . The balloon is then heated to a temperature
of 58C. What is the new volume ?
Since temperature increases, you expect the volume to
increase.
Classwork: p124 # 11, 12 (a-c), 13
Combined Gas Law
 Describes the relationship among the pressure,
temperature and volume, when the amount of gas is
constant.
 P1V1 = P2V2
T1
T2
 Standard temperature and pressure (STP): 0C, 1 atm
 Useful conversions:
1L =1000 mL ; 1mL =1cm3 ; 1dm3 = 1 L
Using the combined gas law:
1. The volume of a gas filled balloon is 30.0L at 313K
and 153 kPa. What would the volume be at standard
temperature and pressure (STP)?
Classwork: p 126 #14(a), 15 (a) , 16, 17,