Half-life calculations
Chemical Kinetics · Chemistry
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A first-order reaction has t₁/₂ = 30 min. How much remains after 90 min? Step 1: 90 min = 3 half-lives. Step 2: After n half-lives: (1/2)ⁿ remains. Step 3: (1/2)³ = 1/8 remains. Step 4: k = 0.693/30 = 0.0231 min⁻¹ (if needed). First order: the fraction remaining depends only on number of half-lives.