## Cracking the AP Chemistry Exam

**Part IV**

**Content Review for the AP Chemistry Exam**

**Chapter 4**

**Big Idea #2: Bonding and Phases**

**THE IDEAL GAS EQUATION**

You can use the ideal gas equation to calculate any of the four variables relating to the gas, provided that you already know the other three.

The Ideal Gas Equation

*PV = nRT*

*P* = the pressure of the gas (atm)

*V* = the volume of the gas (L)

*n* = the number of moles of gas

*R* = the gas constant, 0.0821 L·atm/mol·K

*T* = the absolute temperature of the gas (K)

You can also manipulate the ideal gas equation to figure out how changes in each of its variables affect the other variables.

*P* = the pressure of the gas (atm)

*V* = the volume of the gas (L)

*T* = the absolute temperature of the gas (K)

You should be comfortable with the following simple relationships:

· If the volume is constant: As pressure increases, temperature increases; as temperature increases, pressure increases.

· If the temperature is constant: As pressure increases, volume decreases; as volume increases, pressure decreases. That’s Boyle’s law.

· If the pressure is constant: As temperature increases, volume increases; as volume increases, temperature increases. That’s Charles’s law.