How do you decide when to use this equation: pV=nRT?
Use this equation when you are given three of the four following properties of a gas: pressure, volume, number of moles, and temperature.
This equation is the ideal gas law, which describes the properties of an ideal gas. An ideal gas is a simplified model of real gases, allowing us to use simple formulae and calculations.
For example, to solve for volume, we would require the values of pressure, amount of gas, and temperature.
The ideal gas law will often be used in combination with other gas laws, which are used to calculate gas properties as gases undergo change. These laws are Boyle's Law, Charles's Law, Gay-Lussac's Law, Avogadro's Law, Dalton's Law, the Law of Combining Volumes, and the Combined Gas Law.