Avogadro's Principle

22.4 Liters in one mole

Avogadro's Law: volumes of gases at the same temperature and pressure contain the same number of moles

​There are 22.4 L : 1 mol

Avogadro's Law Calculation

• What Volume does 0.0685 mol of gas occupy at STP?

  • Step one: convert moles of gas to liters​

​0.685 mol

​1 mol

​22.4 L

Avogadro's Law Calculation

• What Quantity of gas, in moles, is contained in 2.21 L at STP?

  • Step one: convert liters of gas to moles

​2.21 L

22.4 L

1 mol

Mass to Mole Review

Calculating Molar Mass

1. Separate each element of the Chemical Formula.

2. Write out the subscripts and find the molar mass for each element

   1. C₆H₁₂O₆

      1. C 6 x 12.01 = 72.06

      1. H 12 x 1.01 = 12.12

      2. O 6 x 16.00 = 96.00

​C₆H₁₂O₆ molar mass = 180.18 g/mol

Review Stoichiometry

How many moles are in 12.5 grams of C₄H₁₀?
C: 4 x 12.01 = 48.04
H: 10 x 1.01 = 10.1
58.14 g/ mol = 58.14 grams : 1 mol

12.5 g C₄H₁₀

1 mol

58.14 g

Avogadro and Stoichiometry

How many Liters are in 12.5 grams of C₄H₁₀?
58.14 g/ mol = 58.14 grams : 1 mol

12.5 g C₄H₁₀

1 mol C₄H₁₀

58.14 g C₄H₁₀

1 mol C₄H₁₀

22.4 L C₄H₁₀

Avogadro and Stoichiometry

How many grams are in 35 L of C₄H₁₀?
58.14 g/ mol = 58.14 grams : 1 mol

35 L C₄H₁₀

1 mol C₄H₁₀

58.14 g C₄H₁₀

1 mol C₄H₁₀

22.4 L C₄H₁₀

Ideal Gas Law

An ideal gas is defined as one in which all collisions between atoms or molecules are perfectly elastic and in which there are no intermolecular attractive forces.

The ideal gas law can be viewed as arising from the kinetic (movement) and pressure of gas molecules colliding with the walls of a container.

A Picky Law

The Ideal Gas Law is considered picky because there are specific units depending on pressure unit.

If a variable is not in the correct unit, you must convert it!

Equation ​PV=nRT

Ideal Gas Law Units

Pressure (P) measured in Pa (pascal)
Volume (V) is L (Liters)
moles (n) mols
Temperature (K) Kelvin
Universal gas constant (R) is 8.314462 (constants never change)

​Equation: PV = nRT

Ideal Gas Law Units

Pressure (P) measured in atm
Volume (V) is L (Liters)
moles (n) mols
Temperature (K) Kelvin
Universal gas constant (R) is 0.0821 (constants never change)

​Equation: PV = nRT

Ideal Gas Law

PV = nRT

where...

Ideal Gas Law Example

If 0.867 moles of nitrogen trioxide is collected at 305.2 K and 0.949 atm, what volume of nitrogen trioxide is present?

Ideal Gas Law Example

P = 0.949 atm

V = ?

n = 0.867 moles

R = 0.0821 L*atm/mol*K 

T = 305.2 K

Ideal Gas Law Example

Let's try another one!

A sample of sulfur trioxide is collected when the atmospheric pressure was 1.21 atm and the room temperature was 22.7 ^oC. It occupies 0.2598L. Calculate the amount of grams of sulfur trioxide present.

Ideal Gas Law Example #2

After converting from Celsius to Kelvin,

P = 1.21 atm

V = 0.2598 L

n = ?

R = 0.0821 L*atm/mol*K

T = 295.85 K