Post on 26-Jan-2016
description
Gases…..
Have neither shape nor volume
Are highly compressible
Diffuse (move spontaneously throughout any
available space until equally distributed)
Temperature affects either the volume or pressure of a gas or both
Pressure
is defined as a force per unit areaSince force can be measured in NewtonsAnd area can be measured in m2
Then N/m2 is the unit which is the SI definition of a pascal
we measure pressure in kilopascal (kPa)
Pressure
Atmospheric pressure is the force per unit area exerted by air on ALL objects
Standard conditions
STP
0 oC101.325 kPa
SATP – more convenient25 0C100kPa
Other pressure units!!
Manometer
Effusion
Boyle’s Law
As pressure on a gas increases, the volume of the gas decreases proportionally, provided that that temperature and the chemical amount(moles) of gas remains constant
So
PV
1
Boyle’s Law
2211
2211
:
:
:
PVPV
Summarized
PVkPVthen
kPVSince
Boyles Law
Volume
Pre
ssu
re
Temperature
is defined as the average kinetic energy of particles
We usually measure it in oC but for gases we will use the absolute or
Kelvin temperature scaleTo convert from celsius simply add 273
Charles’ Law
As temperature of a gas increases, the volume of the gas increases proportionally, provided that that pressure and the chemical amount(moles) of gas remain constant TV
TV
Charles’ Law
2
2
1
1
2
2
1
1
:T
V
T
VCombined
T
Vk
T
Vthen
kT
VSince
Charle's Law
Temperature
Vo
lum
e
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Combined Gas Law
2
2 2
1
1 1
T
Vx P
T
Vx P
• Combination of Boyles and Charles’ Law and (Gay Lussac)
• Unchanging conditions drop out of the equation• Remember temp MUST be in Kelvin
Molar Volume
Molar volume is the volume that one mole of a gas occupies at a specified temperature and pressure…..At STP 22.4 litres in one mole of a gasAt SATP 24.8 litres in one mole of a gas
How do you convert between moles and volume??
How do you convert between mass and volume….one extra step!
Example problem 1
What is the volume of 0.24moles of CO2 (g) at STP??
Example Problem 2
What is the volume of 6.8g of Hydrogen gas at SATP??
Perform the following conversions (all at SATP).
1. 4.00 mol CH4(g) to L
2. 2.25 mol NO(g) to L
3. 4.275 g CO2(g) to L
4. 1.27 g H2(g) to L
5. 5.00 L O2(g) to mol O2(g)
6. 3.50 L H2(g) to mol H2(g)
7. 4.35 L CH4(g) to g CH4(g)
8. 5.45 L N2(g) to g N2(g)
Practice
Section questions #5-10 p. 171
How can you get an egg in and out of a flask?????
Ideal Gas Law
What makes an “ideal gas” hypothetically???
They obey ALL gas laws perfectly under ALL conditions
SO….they do not condense
….graphs of v/T and p/T are straight lines
….particle size is negligible with NO intermolecular attractions between them
REAL gases are most ideal when
Pressure is ? LOW Because…..at high pressure molecules are forced
together and their size becomes significant relative to the empty space in container
Temperature is ? HIGH Because…..at low temperature molecules are
closer together, moving slower and thus experience intermolecular attraction (they condense)
Simulation for Gas Laws
TV
PV
1
nV
pTnV
1
Therefore
24
Ideal Gas Law
PV = nRT
R is called the gas constant (combined gas law constants)
R = 8.314 kPa.L mol.K
Pressure MUST be in kPa and Volume in L and temp in Kelvin
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So many gas laws eh?
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Sample problem 4.4Predict the volume of 0.78g of Hydrogen gas at 22°C and 125kPa
Practice #3-5 p.175 and SQ #8,9,11, p. 176
Explaining Gas Properties
What is kinetic molecular theory??
Kinetic molecular theory
solid(vibrational
)
liquid(vibrational, rotational,
and translational)
gas(translational)
29
Kinetic Molecular Theory
30
Gas PressurePressure = total force applied to a certain area larger force = larger
pressuresmaller area = larger
pressure
• Gas pressure is caused by gas molecules colliding with the container or surface
• More forceful collisions or more frequent collisions mean higher gas pressure
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Compressing a gas!
Law of combining volumes
1809….Joseph Gay-Lussac
Law of combining volumes
1811…Amedeo Avogadro
e.g.
Practice Questions #4-7, p.166 and p168 #1-5