Jump to a New ChapterIntroduction to the SAT IIIntroduction to the SAT II Chemistry TestStrategies for Taking the SAT II Chemistry TestThe Structure of MatterThe States of MatterReaction TypesStoichiometryEquilibrium and Reaction RatesThermodynamicsDescriptive ChemistryLaboratoryBasic Measurement and Calculation ReviewChemical Formulas Review: Nomenclature and Formula WritingPractice Tests Are Your Best Friends
 5.1 Intra- and Intermolecular Forces 5.2 Solids 5.3 Liquids 5.4 Gases 5.5 Phase Changes 5.6 The Gas Laws 5.7 Boyle’s Law 5.8 Charles’s Law

 5.9 Avogadro’s Law 5.10 The Ideal Gas Law 5.11 Density of Gases 5.12 Dalton’s Law of Partial Pressures 5.13 Graham’s Law of Diffusion and Effusion 5.14 Solutions 5.15 Practice Questions 5.16 Explanations
Density of Gases
Since gases are mostly empty space, the densities of gases are reported in g/L, not g/mL as found for solids and liquids. As you’re probably aware, density is equal to mass per unit of volume. To calculate the density of a gas at standard temperature and pressure, you take the molecular formula weight of the gas (grams per mole—from the periodic table) and divide that by the standard molar volume for a gas, which is 22.4 L per mole:
where the formula weight (FW) is in g/mol, and the standard molar volume is 22.4 L/mol. Now try using this in a problem.
Example
What is the density of helium gas at STP?
Explanation
If the density of the gas is equal to , then d = 4.00 g/mol ∏ 22.4 L/mol, so the density = 0.179 g/L.
If conditions are not standard, we can use this expanded version of the ideal gas equation:
Another really handy rearrangement of the ideal gas equation can be used to find the molecular weight of an unknown gas . You’ll get a chance to practice using these in the problems at the end of the chapter. However, there is no need to memorize these last equations since they are all rearrangements of the ideal gas law. Okay, two more important laws and then we’re finished with our discussion of gases, and we move on to solutions.
 Jump to a New ChapterIntroduction to the SAT IIIntroduction to the SAT II Chemistry TestStrategies for Taking the SAT II Chemistry TestThe Structure of MatterThe States of MatterReaction TypesStoichiometryEquilibrium and Reaction RatesThermodynamicsDescriptive ChemistryLaboratoryBasic Measurement and Calculation ReviewChemical Formulas Review: Nomenclature and Formula WritingPractice Tests Are Your Best Friends
Test Prep Centers
SparkCollege
 College Admissions Financial Aid College Life