Unit 9 Notes Guide Name # Gases Block Chemistry

I. Kinetic Molecular Theory Kinetic theory accounts for the behavior of atoms and molecules

o Based on the idea that particles of matter are always in motion

KMT can help to understand the behavior and properties of gases by providing a model for ideal gases

Ideal gas - __________________ gas that perfectly obeys all aspects of the KMT

The 5 Tenets of the Kinetic Molecular Theory

1. Gases consist of molecules in ________________ motion.

2. The molecules of a gas are infinitely __________ points

a. Gases occupy ____ volume

3. Molecules travel in ________________ lines until they ______________.

a. Collisions are ______________, meaning no energy is gained or lost.

4. There are ____ attractive or repulsive ____________ between the molecules.

5. The average ______________ energy of the gas particles is ________________ proportional to

the Kelvin ______________________ of the gas.

a. As temperature _____, KE _____

Characteristics of an Ideal Gas Characteristics of a Real Gas

Assumed to have ________ volume

In constant, ________________ - ________

motion

Experiences ______________ collisions

No ____________________ or

__________________ forces toward each other

Average kinetic energy is proportional to

______________________

Does ______ truly exist

Particles take up space and have ____________

In ________________ motion

Collisions are ______ elastic

Particles have ____________________________

forces

Average kinetic energy is proportional to

temperature

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Why use ideal gases?

o Ideal gases ________________ the model we use to describe gas behavior

o Although ideal gases do not exist, real gases can approach ideal gas behavior under certain

conditions

o Gas behavior is most ideal at ________ volume / ______ pressure and ________ temperature.

II. Physical Properties of Gases Standard Pressure

______ atm = ______________ kPa = ____________ mmHg =____________ torr Density

o The density of a gas is about _____________ the density of the same substance as a liquid or a solid

o Because particles ____________ to fill the container, gases are mostly __________ space, creating a

______ density

Compressibility

o Compressibility – how easily something can be ______________ together

o Because particles are so spread apart, they ____ ______ repel one another very much if volume were

to decrease, so they are ____________ compressible

o Notice how ____________________ volume __________________ pressure

Graham’s Law of Effusion

o Effusion – movement through a small ________ in a container (similar to diffusion)

o Graham’s Law of Effusion – a gas will effuse at a ________ that is __________________

proportional to the square root of its __________ ________

o Small particles with ______________ molar masses move ____________

Example: An unknown gas effuses 1.66 times more rapidly than CO2. What is the molar mass of the unknown gas.

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TimeA=TimeB(RateB

Rate A)

III. Partial Pressure All gases exert ________________ on their container

Dalton’s Law – the __________ pressure of a gas mixture is the ______ of the ______________

pressure exert by __________________ gases in the mixture

PTotal=P1+P2+ P3…

The partial pressure of each gas is equal to the ________ ________________ (X) of each gas times the total pressure

Example 1: What is the total pressure of a gas containing He exerting 0.2 atm of pressure, O2 exerting 988 torr of pressure, and N2 exerting 4.9 atm of pressure?

Example 2: What is the partial pressure exerted by oxygen if a mixture of 5 moles of O2 and 1 mole of H2 exerts a total pressure of 12 atm?

IV. Gas Laws Temperature must be in units of ____________ for all gas laws

Boyle’s Law

o At constant temperature with the same amount of gas, as

________________ of a gas __________________, the

volume __________________.

o Pressure and volume are __________________ related.

o Mathematically, Boyle’s Law is expressed as: P1V 1=P2V 2

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Mole fraction( X)=moles of gastotalmoles

Example: A sample of neon occupies a volume of 461 mL at STP. What will be the volume of the neon when the pressure is reduced to 93.3 kPa?

Charles’ Law

o At constant pressure with the same amount of gas, as

______________________ of a gas __________________, the

volume __________________.

o Temperature and volume are ___________________ related.

o Mathematically, Boyle’s Law is expressed as:V 1

T 1=

V 2

T2

Example: A 600 mL sample of nitrogen is heated from 27C to 77C at constant pressure. What is the final volume?

The Combined Gas Law

o Combines Boyle’s and Charles’ Laws into one equation, holding only the ____________ (moles) of gas constant

P1V 1

T 1=

P2V 2

T 2

Example: A gas takes up a volume of 17 liters, has a pressure of 2.3 atm, and a temperature of 299K. If I raise the temperature to 350 K and lower the pressure to 1.5 atm, what is the new volume of the gas?

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Gas Laws Graphic OrganizerBoyle’s Law Charles’ Law Combined Gas Law

Description

For a given amount of gas at constant temperature, the

volume of a gas varies inversely with pressure

The volume of a gas is directly proportional to its Kelvin temperature if the pressure is kept constant

Combines Boyle’s and Charles’ Law into one

equation

Law

Graph N/A

Relationship N/A

What is held constant?

Units

Pressure –

Volume –

Temperature –

Volume –

Pressure –

Volume –

Temperature –

Temperature Pressure Volume Standard Conditions (STP)

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K (¿℃)=¿ 1 atm=¿ ¿ ¿

1cm3=¿

1dm3=¿

V. Gas Stoichiometry Avogadro’s Principle – Equal ______________ of gases at the same temperature and pressure contain

an __________number of __________________.

Molar Volume – volume that one ________ of ________ gas occupies at ________

1 mol of gas = 22.4 Lo The size of gas particles is so __________ relative to the amount of __________ __________

that the difference between large and small particles does ______ change volume

Example 1: What is the volume of 3.5 moles of gas at STP?

Example 2: What is the volume of 44 g of O2 at STP?

The Ideal Gas Lawo Assuming conditions of STP and one mole of gas, the combined gas law simplifies to a constant R

known as the __________________ ______ ________________.

o The value and units of the ideal gas constant depend on the units of ________________.

o Since we will not always have one mole of gas, the ideal gas constant must be multiplied by the

number of __________. ( PVT

=nR)

o Rearranged: PV =nRT

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P = pressure (in atm or kPa)V = volume (in L)n = number of molesR = Ideal gas constant

0.0821 L∙ atmmol ∙ K or 8.314 L ∙kPa

mol ∙ K

Example 1: If I have 4 moles of as at a pressure of 5.6 atm and a volume of 12 liters, what is the temperature?

Example 2: If I have an unknown quantity of gas at a pressure of 121.6 kPa, a volume of 31 liters and a temperature of 87C, how many moles of gas do I have?

VI. Equilibrium

Volume and pressure _________ effect the equilibrium of ____________

A ________________ in volume (______________ in pressure) will shift equilibrium towards the side

with the ____________ moles of gas.

o The ______________ and ________ of gas molecules does ______ matter

If volume were increased (________________ in pressure) shifts equilibrium towards

the side with the ________ moles of gas

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P = pressure (in atm or kPa)V = volume (in L)n = number of molesR = Ideal gas constant

0.0821 L∙ atmmol ∙ K or 8.314 L ∙kPa

mol ∙ K