Gases & the kinetic molecular theory

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Gases & the kinetic molecular theory

Chemistry

Gases & the Kinetic Molecular Theory

Properties of Gases

Matter exists in three states: solids, liquids, and gases.
A vapor is a gas that has formed either by the evaporation of a liquid or the sublimation of a solid.
The density of gases is significantly less than liquids and solids – this indicates that the gas molecules are far apart relative to their size and their interactions are weak
Gases are easily compressed and fill their container
The interactions of gases would be minimal b/c of the molecules are so far apart if were not for their rapid motion.

Properties of Gases:

Gases can be compressed into smaller volumes; their densities can be increased by increasing pressure
Gases exert pressure on their surroundings; therefore, pressure must be exerted to be confined
Gases expand w/out limits; so gases can uniformly and completely occupy the volume of any container
Gases diffuse into one another; meaning that gases placed in the same container mix completely and cannot separate on standing
The amounts and properties of gases are describe in terms of temperature, pressure, volume occupied and number of molecules

Basics

Pressure = force/area
What is a barometer?
What is a manometer?
Know the units of pressure: torr, mm Hg, and atm
Be able to convert b/t all 3 units of pressure: 1 atm = 760 mm Hg at 0^oC = 760 torr
The SI unit of pressure is the pascal (Pa)
1 atm = 101.325 kPa

Boyle’s Law

Know Boyle’s Law: expresses the relationship between volume and pressure

P₁V₁ = P₂V₂ (constant n, T) Remember: n = moles

Charles’s Law

Know Charles’s Law: expresses the relationship between volume and temperature (in Kelvin)

(constant n, P)

STP

Standard Temperature and Pressure (STP) = 0^oC (273 K) and 1 atm

Combined Gas Law

Know the Combined Gas Law

(at constant n)

Avogadro’s Law

Know Avogadro’s Law

(at constant T,P)

Avogadro’s Law led to the Standard Molar Volume: 1 mole of a gas = 22.4 L at STP

Ideal Gas Law

Know the Ideal Gas Law

PV = nRT

R is the Universal Gas Constant
R = 0.0821 L atm/ mol K
R = 8.314J/mol K
You decide which R to use based on the units

Additional Information

Be able to do solve for molecular weights of gases using the Ideal Gas Law
By solving for n you can get moles; then using the provided mass solve for the molecular weight

Dalton’s Law

Know Dalton’s Law of Partial Pressure – the total pressure exerted by a mixture of gases is the sum of the partial pressures of the each gas.

P_total= P₁ + P₂ + P₃ + …

For gases collected over water you must take into consideration that the gas is saturated with water vapor. (P_atm is the atmospheric pressure)

P_atm = P_gas + P_water

So if you are trying to solve for the pressure of the gas:

P_gas= P_atm - P_water

Gas Stoiciometry

Be able to complete stoichiometric calculations for reactions with gases.

Remember that for gases 22.4 L = 1 mol at STP

If the conditions are not at STP you must use the Ideal Gas Law to solve for moles and then do your stoichiometry

KMT

Know the Kinetic Molecular Theory

#1. Gas is composed of particles- usually molecules or atoms
#2. Particles in a gas move rapidly in constant random motion
#3. Collisions are perfectly elastic, no energy is lost or gained
#4. Between collisions, the molecules exert no attractive or repulsive forces on each other

Diffusion/Effusion

Know what diffusion is.
Know what effusion is.
How does molecular size affect effusion/diffusion
From a group of substances be able to determine which would have greatest rate of effusion/diffusion
Know Graham’s Law

Real Gases

Know how real gases deviate from ideal gases
Non-ideal gas behavior is greatest when the gas is at high pressure and/or low temp. ( near liquefaction)

Source : http://teachers.greenville.k12.sc.us/sites/jhushen/AP%20Chemistry%20Resources/Chapter%205%20Gases/AP%20Chemistry%20Chapter5%20Study%20Guide.doc

Web site link: http://teachers.greenville.k12.sc.us

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