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Gases & Atmospheric ChemistryGases; a unique state of matter following their own laws and displaying interesting chemical behaviourhttp://www.youtube.com/watch?v=Zz95_VvTxZM

Gases Are Special State of Matter: Gases can be compressed, solids &

liquids cannot

Kinetic Molecular Theory: All particles of solids, liquids & gases display constant random motion

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Solids Liquids Gases

Types of Motion

Vibrational Vibrational, Rotational & Translational

Vibrational, Rotational & Translational

Strength of Attraction

Strongest Intermediate Weakest

Organization of Particles

Highly Organized Intermediate Very Low

TemperatureMeasures the average kinetic

energy of particles in a substance

Kinetic energy is the energy of movement

The temp. of a gas, greatly affects its behaviour

Measured in Kelvins (K)0o C = 273 K

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PressureThe force exerted on a surface,

per unit of areaThe standard unit (SI) of

pressure is the Pascal (Pa)1 Pa = 1 N/m2, (1 Newton of

force exerted over a 1 m2 surface)

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Atmospheric PressureThe pressure of the large mass of air pressing

down on the surface of the Earth is called Atmospheric pressure

Standard atmospheric pressure at sea level is 101,325 Pa, because this is such a large number, we usually express it as 101.325 kPa (kilopascals)

STP: standard temp & press; 0oC & 101.325kPa

SATP: standard ambient temp & press; 25oC & 100 kPa

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Units of PressureBecause 101.3 kPa is standard, we can say

101.3 kPa = 1 atm (atmosphere)Other units of pressure include:

Millimetres Mercury; 760 mmHg = 1 atm (used in biology)

Torr; 760 torr = 1 atm (used in physics)Pounds per Square Inch; 1 atm = 14.696

psi (used in industry)

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Boyle’s Law At any constant temperature, the

multiplication product of the pressure and the volume of any size sample of any gas is a constant.

To express it mathematically, we use the equation:

P1V1 = P2V2

The pressure and the volume are inversely proportional; as the pressure increases the volume of the sample of gas must decrease

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Boyle’s Law

P vs. V

P vs. 1/V

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Charles’ Law At constant pressure, the mathematical product of

the temperature and the inverse volume of any size sample of any gas is a constant

To express it mathematically, we use the equation:

V1T2= V2T1

The pressure and the volume are directly proportional; as the temperature increases the volume of the sample of gas must also increase

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Charles’ Law V vs. T

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Gay-Lussac’s Law At constant volume, the mathematical product of

the temperature and the inverse pressure of any size sample of any gas is a constant

To express it mathematically, we use the equation:

P1T2= P2T1

The pressure and temp are directly proportional; as the temp increases the pressure of the sample of gas must also increase

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Gay-Lussac’s Law P vs. T

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The Combined Gas Law Encompasses Charles + Boyle + Gay-Lussac

together for a constant amount of gas

To express it mathematically, we use the equation:

P1V1T2= P2V2T1

Keeping P, V or T constant is difficult to do in the lab. The Combined Law allows us to bypass this

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Avogadro’s Law The volume of gas is directly proportional to the

amount of gas present Example: 1 mole of O2 will occupy the SAME volume as 1 mole of CO2,

under the same conditons of pressure and temperature

To express it mathematically, we use the equation:V1n2= V2n1

Any 1 mol sample of gas occupies 22.4 L at 0oC and 1 atm pressure (STP)

Any 1 mol sample of gas at occupies 24.8 L at 25oC and 100 kPa pressure (SATP)

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Ideal Gas Law All gases, no matter the chemical, show remarkably similar properties Pressure, volume, temperature and molar amounts of gas yield the following:

PV/nT = R

R is the universal gas constant: when using kPa, R = 8.3143510  kPa L/mol K when using atm, R = 0.08206 L atm/mol K

This equation is the most important, because it allows us to use easily measureable values (P,V & T) to determine molar amounts (n)

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Dalton’s Law of Partial Pressure

When Dalton was conducting his atomic theory studies, he also included studies of the behavior of gases in 1803.

For a mixture of gases in a container, the total pressure exerted is the sum of the pressures that each gas would exert if it were alone.  This law can be expressed in equation form as:  

p = p1 + p2 + p3 + ...

where p is the total or measured pressure and p1, p2, ... are the partial pressures of the individual gases

For air, an appropriate form of Dalton's law would be:p(air) = p(N2) + p(O2) + p(CO2) + ...

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Composition of Dry Air at Sea Level

ComponentMole

PercentMolar Mass

N2 78.08  28.013

 O2 20.948 31.998

Ar 0.934 29.948

CO2  0.0314 44.010

Ne  0.001818 20.183

He  0.000524 4.003

CH4 0.002 16.043

Kr 0.000114 83.80

H2 0.00005 2.016

N2O 0.00005 44.013

Xe 0.0000087 131.30

Gas Reactions

Because of Avogadro’s Law, reactions with gases are easy to work with in terms of stoichiometry

2 CO(g) + 1 O2(g) 2 CO2(g)

Ex: If we start with 65.0L of CO; because of the 2 CO: 1 O2 ratio, we can easily predict that 32.5L of O2 will be required to fully react

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