**Definition**: Dalton’s Law of Partial Pressures states that the total pressure of a gas mixture is equal to the sum of all individual or partial pressures of its component gases.

P_{total} = P_{1} + P_{2} + P_{3}

Partial pressures are proportional to each gas’ mole fraction (how much of the gas is present in the mixture).

To find Mole Fraction:

To find the Partial Pressure for each gas in mixture:

P_{1}= (P_{total}) (X_{1}) ….and so on for each gas in the mixture

To find Total Pressure: P_{total} = P_{1 }+ P_{2} + P_{3}

**Problem**: A sample of natural gas contains 8.24 moles of CH_{4}, 0.421 moles of C_{2}H_{6}, and 0.116 moles of C_{3}H_{8}. If the total pressure of the gases is 1.37 atm, what is the partial pressure of propane (C_{3}H_{8})?

GIVEN:

Moles CH_{4} = 8.24

Moles C_{2}H_{6} = 0.421

Moles C_{3}H_{8} = 0.116

P_{Total} = 1.37 atm

**Part I**: Find total number of moles

8.24 + 0.421 + 0.116 = 8.777 mols

**Part II**: Find the mole fraction for proprane (C_{3}H_{8})

**Part III**: Find the partial pressure of proprane (C_{3}H_{8})