Study guides › C/P › General Chemistry
Gases
This chapter covers gas pressure, the simple gas laws, the ideal gas law, partial pressures, kinetic molecular theory, effusion, and real-gas deviations. You will solve gas problems with clean numbers and read the standard graphs.
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What this chapter covers
- Pressure & the Simple Gas Laws. Boyle, Charles, and Gay-Lussac problems are quick points if you always use Kelvin and know which variable is held constant.
- The Ideal Gas Law, STP & Gas Stoichiometry. PV = nRT ties every gas variable together, so it solves density, molar mass, and yield problems.
- Gas Mixtures & Dalton's Law. Partial pressures follow mole fractions, and gases collected over water need a vapor-pressure correction.
- Kinetic Molecular Theory, Effusion & Graham's Law. KMT explains why temperature measures kinetic energy, and Graham's law is a favorite quick square-root calculation.
- Real Gases & Deviations from Ideality. The MCAT asks when PV = nRT breaks down and which gas is least ideal, and both answers come from intermolecular forces and molecular size.
Key points to know
- 1 atm = 760 torr = 760 mmHg = 101.3 kPa
- Boyle: PV constant; Charles: V/T constant; Gay-Lussac: P/T constant
- PV = nRT with R = 0.0821 L·atm/(mol·K)
- STP = 273 K, 1 atm; molar volume = 22.4 L
- Total pressure = sum of partial pressures
- Partial pressure = mole fraction × total pressure
- Average KE depends only on temperature: KE = (3/2)k_BT
- Lighter gas molecules are faster at the same T
Try a practice question
Which statement correctly expresses Boyle's law?
- At fixed n and T, the product P × V is constant
- At fixed n and P, V/T is constant
- At fixed n and V, P/T is constant
- At fixed T and P, V/n is constant
Show the answer
A. Boyle's law relates pressure and volume at constant temperature and amount, so PV is constant. The other statements are Charles's, Gay-Lussac's, and Avogadro's laws.
Common questions
What does this chapter cover?
Gases covers Pressure & the Simple Gas Laws, The Ideal Gas Law, STP & Gas Stoichiometry, Gas Mixtures & Dalton's Law, Kinetic Molecular Theory, Effusion & Graham's Law, Real Gases & Deviations from Ideality.
What should I know first?
1 atm = 760 torr = 760 mmHg = 101.3 kPa Boyle: PV constant; Charles: V/T constant; Gay-Lussac: P/T constant PV = nRT with R = 0.0821 L·atm/(mol·K)
24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.