Half-Life Concentration Hacks: Mnemonics for Reaction Orders!
“Half-Life vs. [A]₀” Mnemonics
1. Movement Mnemonic (Visualize Actions)
“Zero Lifts, First Flies, Second Sinks, Third Dives!”
- Zero order (↑): Lift hands ↑ (t½ increases with [A]₀)
- First order (→): Flat hand → (t½ independent of [A]₀)
- Second order (↓): Hand sinks ↓ (t½ decreases with [A]₀)
- Third order (↓↓): Both hands dive ↓↓ (t½ decreases sharply with [A]₀)
2. Arrow Pattern (Write This)
↑ → ↓ ↓
(Order 0: ↑ | Order 1: → | Order 2: ↓ | Order 3: ↓↓)
3. Quick Phrase (Verbal)
“Up, Flat, Down, Downer!”
- “Up”: Zero order (↑)
- “Flat”: First order (→)
- “Down”: Second order (↓)
- “Downer”: Third order (↓↓)
Why It Works
| Order | t½ Formula | Effect of ↑[A]₀ on t½ | Mnemonic Key |
|---|---|---|---|
| 0 | t½ = [A]₀/(2k) | Increases (↑) | “Lifts” / “Up” |
| 1 | t½ = ln(2)/k | Unaffected (→) | “Flies” / “Flat” |
| 2 | t½ = 1/(k[A]₀) | Decreases (↓) | “Sinks” / “Down” |
| 3 | t½ = 3/(2k[A]₀²) | Decreases sharply (↓↓) | “Dives” / “Downer” |
Formula Pattern (Bonus)
Notice the exponent of [A]₀ in t½ formulas:
- Order 0: [A]₀¹ ➜ ↑
- Order 1: [A]₀⁰ ➜ →
- Order 2: [A]₀⁻¹ ➜ ↓
- Order 3: [A]₀⁻² ➜ ↓↓
Remember: “Positive exponent? Half-life climbs!”
