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📘 Lesson 5 of 10 · Thermodynamics

💨 Gas Laws

The gas laws describe precise relationships between a gas's pressure, volume, temperature, and amount — remarkably simple equations that explain everything from balloons to car engines.

Course progress: 50%

01 Key Concepts

Boyle's Law

At constant temperature, pressure and volume are inversely related: P1*V1 = P2*V2.

Charles's Law

At constant pressure, volume and temperature (in Kelvin) are directly proportional: V1/T1 = V2/T2.

Gay-Lussac's Law

At constant volume, pressure and temperature (in Kelvin) are directly proportional: P1/T1 = P2/T2.

The Combined Gas Law

Merges all three: (P1*V1)/T1 = (P2*V2)/T2, useful when pressure, volume, and temperature all change together.

The Ideal Gas Law

PV = nRT, where n is the number of moles of gas and R is the universal gas constant (8.314 J/(mol*K)) -- relates all four key gas variables at once.

02 Key Formulas

03 Solved Examples

Example 1 A gas has volume 4L at pressure 2 atm. Find its volume if pressure increases to 8 atm (constant temperature).
  1. Apply Boyle's Law: P1*V1 = P2*V2.
  2. 2*4 = 8*V2.
  3. 8 = 8*V2, so V2 = 1.
Answer: 1 L
Example 2 A gas has volume 2L at 300K. Find its volume at 600K (constant pressure).
  1. Apply Charles's Law: V1/T1 = V2/T2.
  2. 2/300 = V2/600.
  3. V2 = 2*600/300.
Answer: 4 L
Example 3 A gas has pressure 1 atm at volume 10L and temperature 250K. Find its pressure at volume 5L and temperature 500K.
  1. Apply the combined gas law: (P1*V1)/T1 = (P2*V2)/T2.
  2. (1*10)/250 = (P2*5)/500.
  3. 10/250 = 5*P2/500.
  4. 0.04 = P2/100, so P2 = 4.
Answer: 4 atm

04 Practice Questions

1A gas has volume 6L at pressure 3 atm. Find volume at 9 atm (Boyle's Law).
P1V1=P2V2: 18=9*V2, V2=2L
2A gas has volume 3L at 200K. Find volume at 400K (Charles's Law).
3/200=V2/400, V2=6L
3What variables does Boyle's Law relate at constant temperature?
Pressure and volume
4What variables does Charles's Law relate at constant pressure?
Volume and temperature
5What does the ideal gas law PV=nRT include that the other gas laws don't?
The number of moles (n) of gas

📄 Gas Laws — Downloadable Worksheet

10 questions with a full answer key. Grab the PDF to print, or try the interactive version in your browser.

🗒 Cheat Sheet ⬇ Download PDF 🖥 Interactive Worksheet