The ideal gas law is the most important gas law for you to know: itcombines all of the laws you learned about in this chapter thus far,under a set of standard conditions. The four conditions used todescribe a gas—pressure, volume, temperature, and number of moles(quantity)—are all related, along with
R, the universal gas law constant, in the following formula:
PV = nRT
where
P = pressure (atm),
V = volume (L),
n = number of moles (mol),
R = 0.08206 L · atm/mol · K, and
T = temperature (K).
Now try an example using the ideal gas law equation.
Example
A 16.0 g sample of methane gas, CH4, the gas used in chemistry lab, has a volume of 5.0 L at 27ºC. Calculate the pressure.
Explanation
Looking at all the information given, youhave a mass, a volume, and a temperature, and you need to find thepressure of the system. As always, start by checking your units. Youmust first convert 16.0 g of CH4 into moles: 16.0 g CH4
1 mol CH4/16.0 g CH4= 1 mol of methane. The volume is in the correct units, but you mustconvert the temperature into Kelvins: 27 + 273 = 300K. Now you’re readyto plug these numbers into the ideal gas law equation:
PV = nRT
(P) (5.0 L) = (1.0 mol) (0.0821 L
atm/mol
K) (300K), so P = 4.9 atm
Don't let the math scare you. Remember thatyour test will be all multiple choice. You may be asked for propersetup, or at least you will have answers to choose from, and you won'thave to do these lengthy calculations without a calculator. Theseexamples are only meant to give you practice using the gas lawequations.
