Gas Laws — Chemistry Mnemonic
Target: mnemonic for gas laws chemistry Boyle Charles ideal gas
Why is this hard to memorize?
Gas laws describe the behaviour of gases under varying conditions of pressure, volume, and temperature. For NEET and JEE, you need: Boyle's Law (P∝1/V at constant T), Charles's Law (V∝T at constant P), Gay-Lussac's Law (P∝T at constant V), Avogadro's Law (V∝n at constant P,T), Combined Gas Law (PV/T = constant), and the Ideal Gas Equation (PV = nRT). You also need Dalton's Law of partial pressures and Graham's Law of diffusion. The challenge is remembering which variables are held constant for each law — a mnemonic that links law → relationship → constant variable is essential.
Classic mnemonics you should know
"Boyle=PV(constant T), Charles=VT(constant P), Gay-Lussac=PT(constant V)"
Each law relates two variables while keeping the third constant: Boyle(P↕V at T), Charles(V↕T at P), Gay-Lussac(P↕T at V). Remember which two change and which stays.
"PV = nRT — "Pavan Runs Towards" or "Please Visit Next Room Tomorrow""
PV = nRT combines everything. P=pressure, V=volume, n=moles, R=gas constant (8.314 J/mol·K or 0.0821 L·atm/mol·K), T=temperature in Kelvin. This single equation handles all gas problems.
"Boyle: P↑ V↓ (inverse). Charles: V↑ T↑ (direct). Gay-Lussac: P↑ T↑ (direct)"
Boyle's law is the only inverse relationship (squeeze more → smaller volume). Both Charles and Gay-Lussac are direct (heat more → more volume or more pressure). This is why balloons expand in heat and pop in the sun.
The complete list
- Boyle's Law (PV = constant at constant T)
- Charles's Law (V/T = constant at constant P)
- Gay-Lussac's Law (P/T = constant at constant V)
- Avogadro's Law (V/n = constant at constant P,T)
- Ideal Gas Law (PV = nRT)
- Dalton's Law (P_total = P₁ + P₂ + ...)
- Graham's Law (rate ∝ 1/√M)
Frequently asked questions
How do I remember which gas law has which variables?
Use the initials: Boyle(B) has P and V (PV). Charles(C) has V and T (VT). Gay-Lussac(GL) has P and T (PT). The "missing" variable is held constant. Or just use PV=nRT for everything — it contains all individual laws.
What value of R should I use in NEET?
It depends on units: If P is in atm and V in litres → R = 0.0821 L·atm/(mol·K). If P is in Pa and V in m³ → R = 8.314 J/(mol·K). NEET usually gives the value, but JEE may expect you to remember 8.314.
Why must temperature be in Kelvin for gas laws?
Gas laws relate volume/pressure to ABSOLUTE temperature. At 0°C, gas molecules still have kinetic energy — they don't stop. Kelvin starts at absolute zero (−273.15°C) where molecular motion theoretically ceases. Using Celsius would give wrong proportionalities because 0°C ≠ zero energy.
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