Collision theory
Chemical Kinetics · Chemistry
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Study notes
Why does H₂ + I₂ → 2HI proceed but with far fewer successes than collisions? Step 1: At 700 K, Z ≈ 10²⁸ collisions/L·s — enormous. Step 2: Fraction with E ≥ E_a (165 kJ/mol): e^(−165000/(8.314×700)) ≈ 10⁻¹². Step 3: Effective collisions ≈ 10²⁸ × 10⁻¹² = 10¹⁶ — still plenty. Step 4: Orientation factor p trims further — H–H must meet I–I end-on-ish. Three filters: collide, energetic, aligned.