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=
*n*RT

○ 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