Chemistry IIUnit 1 Gases

The Nature of GasesObjectives:1. Describe the assumption of the kinetic

theory as it applies to gases.2. Interpret gas pressure in terms of kinetic

theory3. 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 densityCompressibleMixtures are homogeneousFluids (flow)

Gas pressureResults 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 kPa1kpa = 1000 paStandard pressure: 1 atm

Factors affecting gas pressureAmount of gas Volume Temperature

Standard temperature : 0C (273K)

Converting between units of pressure1. 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.kPaFor converting to mmHg:

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 103-105Do problems 1,4,5,6

Gas LawsObjectives1. Describe the relationships among the

temperature, pressure, and volume of a gas2. Use the gas laws to solve problems

Boyle’s Law : Pressure and VolumeStates 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 1: initial condition V: volume 2: final condition

YouTube - Self Inflating a BalloonMarshmallow Man In A Vacuum (Family & Education: Cool Experiments)

Using Boyle’s Law1. 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 = P2 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 = P2 x V2

Classwork: pg 121 #1 (a-c), 2, 3, 4

Charles’s Law: Temperature and VolumeStates that the temperature of an enclosed

gas varies directly with the volume at constant pressure.

As temperature increases, volume increases.

V1 = V2T1 T2V1: initial volume V2: final volumeT1: initial temperature T2: final

temperatureTemperature has to be in Kelvin scale.K =C + 273

Volume and Temperature

As a gas is heated, it expands.This causes the density of thegas to decrease.

YouTube - Balloon in liquid nitrogen

Using Charles’s Law1. A balloon inflated in a room at 24C has a

volume of 4.00L . The balloon is then heated to a temperature of 58C. What is the new volume ?

Since temperature increases, you expect the volume to increase. Classwork: p124 # 11, 12 (a-c), 13

Combined Gas LawDescribes the relationship among the

pressure, temperature and volume, when the amount of gas is constant.

P1V1 = P2V2 T1 T2Standard temperature and pressure (STP):

0C, 1 atmUseful 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,