80% of a first order reaction was completed in 70 min. What is the half life of the reaction?

Explanation

To find the half-life of a first-order reaction where 80% of the reaction is completed in 70 minutes, we can follow these steps:

### Step 1: Understand the reaction completion
In a first-order reaction, if 80% of the reactant is consumed, then 20% remains. If we assume the initial concentration (A0) is 1, then at the time when 80% is completed, the concentration (A) will be:
\[ A = A_0 - 0.8A_0 = 1 - 0.8 = 0.2 \]

### Step 2: Use the first-order rate equation
The rate constant \( k \) for a first-order reaction can be calculated using the equation:
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