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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
1
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.
2
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
3
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?
4
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)
5
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
6
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