Quantum yield
Photochemistry · Chemistry
Study notes
Photolysis of HI: 2HI + hν → H₂ + I₂. 10¹⁸ photons absorbed, 2×10¹⁸ HI molecules decomposed. Find Φ. Step 1: Φ = molecules reacted / photons absorbed. Step 2: Φ = 2×10¹⁸ / 10¹⁸ = 2. Step 3: Φ = 2 (not 1!) reveals a secondary reaction: H + HI → H₂ + I also occurs. Step 4: Quantum yield exposes hidden mechanism steps.