A Gas (Review)

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


  • 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 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