## How to Solve a Partial Pressure Problem

Introduction

In a mixture of gases, the pressure of each individual gas is known as the partial pressure. The partial pressure of each gas is related to the number of moles of the gas.

*For an analogy see*

*Ideal Gas Law Explained By Analogy.*

**Equations to know:**

Px = P

P

P

n

n

_{Total}( n_{x}/ n_{Total})P

_{x}= partial pressure of gas xP

_{Total}= total pressure of all gasesn

_{x}= number of moles of gas xn

_{Total}= number of moles of all gases**Example Problem:**

A balloon contains 0.2 moles of nitrogen and 0.5 moles of oxygen. If the total pressure in the balloon is 2.0 atm, what is the partial pressure of oxygen?

### Instructions

#### Step 1

Identify all of the known and unknowns in the partial pressure equation.

### Example

#### Step 1

P

_{x}= This is the partial pressure of oxygen, our unknown

P

_{Total}= 2.0 atm

n

_{x}= 0.5 moles of oxygen

n

_{Total}= 0.5 moles + 0.2 moles = 0.7 moles

#### Step 2

Plug in the numbers and solve for the unknown (in this case it is P

_{x}).

#### Step 2

We use the following equation:

P

_{x}= P

_{Total}( n

_{x}/ n

_{Total})

P

_{x}= 2.0 atm (0.5 moles/0.7 moles) =

**1.4 atm**