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
Avogadro’s Law
- 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 fraction
Moles of gas / total gas moles (unitless)
○ 
Valve Questions
- Have to use Boyle’s law to find P₂ and then add them up to calculate Ptotal