A Gas (Review)

• Uniformly fills any container (have variable volume)
• Mixes spontaneously and completely with any other gas
• Exerts pressure on its surroundings

Pressure

• Is equal to force/unit area
• Pressure equals the number of collisions with the particles and its container

○ Collision = force; container = area → more collisions = higher pressure

• Gasses have random motions and travel at high speeds → when they strike the side of the container they exert a force on that area = pressure
• SI units = newton/meter² = 1 Pascal (Pa)

The Gas Laws

Boyle’s Law

• Pressure and volume (and KE) are inversely related

○ Temperature must be constant

• Units do not matter as long as they are the same on both sides
• A gas that strictly obeys Boyle’s law is called an ideal gas

Charles Law

• The volume of a gas is directly proportional to temperature

○ Pressure must be constant

• In all gas laws, temperature must be in kelvin
• Gas is heated to a higher temperature → avg KE & speed of gas increase → they hit the walls more often/with more force.

○ In order to keep the pressure constant, need to increase the volume of the container

• The volume of a gas is directly proportional to the number of moles of gas

○ Temperature and pressure must be constant

Gay-Lussac’s Law

• Pressure and temperature are directly related

○ Volume must be constant

Combined Gas Laws

• Not that common on AP exam
• If the moles of gas remains constant, use this formula and cancel out the other things that don’t change

The Ideal Gas Laws

• PV=nRT

○ P = pressure in atm, torr, kPa

○ V = volume in liters

○ n = moles

○ T = temperature in Kelvin

○ R = ideal/universal gas constant (on reference sheet)

■ = 0.08206 L atm K^-1 mol ^-1

■ = 62.4 L torr K^-1 mol^-1

■ = 8.314 L kPa K^-1 mol^-1

• A gas that obeys this equation is said to behave ideally
• Assumes that particles have no attraction or volume

Gas Stoichiometry

• Standard Temperature and Pressure (STP): The conditions 0 ℃ and 1 atm

○ The molar volume of an ideal gas is 22.42 L at STP

Gas Density and Molar Mass

Dalton’s Law of Partial Pressure

• Dalton’s law of partial pressures: the final total pressure is the same as the sum of of the initial pressures of each gas

○

○ epresent each partial pressure: the pressure that a particular gas would exert if it were alone in the container.

• Under constant T and V, doubling the moles of a gas will double its partial pressure
• Partial Pressure Formula:

Mole fractionMoles of gas / total gas moles (unitless)

○

Valve Questions

• Have to use Boyle’s law to find Pand then add them up to calculate Ptotal