Chemistry Week 13

Pressure

• Represented by P

• Caused by collisions of molecules with wall of container

• Must be in atm when using the ideal gas law

Volume

• Represented by V

• Must be in liters when using the ideal gas law

Moles of gas

• Represented by n

• Must be in moles when using the ideal gas law

Temperature

• Represented by T

• Must be in K when using the ideal gas law

- Convert C to K by adding 273.15

The Ideal Gas Law

• Used to solve for the behavior of an ideal gas, relating pressure, volume, amount of gas, and temperature

• Combination of Avogadro’s Law, Charles’ Law, Amonton’s Law or Gat-Lussac’s Law, and Amonton’s Law or Gat-Lussac’s Law

• Formula: PV=nRT

Ideal gas constant

• Represented by R

• Value: 0.08206 (L*atm)/(mol*k)

• Derived from the four k constants

Initial Condision - Final Condition

• Step 1: Place initial conditions equal to final conditions

• Step 2: Remove any variables that remain constant

• Note: A variable being constant can be implied

- Ex: Gas inside a container is heated, the volume is constant because there is no mention of the container being changed

• Note: A variable being constant can be explicitly stated

- Ex: The temperature does not change

Standard temp. and pressure

• 0 °C or 273 K and 1 atm pressure

• One mole of grass takes up roughly 22.4L of space at this temperature

Molar Volume

• Volume occupied by 1 mole of a gas at STP

• Formula: V = nRT/P

• About 22.4 L per mole

Density

• How compact something is

• Formula: d = mass/V

Ideal Gas

• Gas that doesn’t interact with any molecules in any way, except physically colliding with them

Normal Atmospheric Pressure

• Pressure of the air at sea level

• Value: 760mmHg = 760torr = 1atm

Amonton’s Law or Gat-Lussac’s Law

• States that pressure (P) is directly proportional to its temperature (T)

- Assuming V and n are constant

Charles’ Law

• States that volume (V) is directly proportional to its temperature (T)

- Assuming P and n are constant

Avogadro’s Law

• States that volume (V) is directly proportional to the amount of moles of gas (n)

- Assuming T and P are constant

Relating Molar Mass to Density

Molar Mass from Ideal Gas Equation

• Step 1: Redefine molar mass equation (M = grams/mole) as M = m/n

• Step 2: Rearrange redefined equation (M = m/n) into n = m/M

• Step 3: Plug rearranged formula into Ideal Gas Law (PV = nRT)

- Resulting formula: PV = (m/M)RT

Molar Mass Equation

• Molar mass equation: M = grams/mole

Room mean square speed

• The average kinetic energy of a molecule

• Represented by variable Urms

Dalton’s Law

• The sum of the partial pressures of all ideal gases in a container equals the total pressure of the mixture

Diffusion

• The unrestricted dispersal of molecules through space, completely random

Effusion

• Diffusion through a very small opening in a physical barrier

• Larger molecules have trouble passing through opening