After 40.0 min, 22.0% of a compound has decomposed. What is the half-life of this reaction assuming first-order kinetics? min

Chemistry
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Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
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Chapter1: Chemical Foundations
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**Problem Statement:**
After 40.0 minutes, 22.0% of a compound has decomposed. What is the half-life of this reaction assuming first-order kinetics?

**Calculation Area:**
\[ t_{1/2} = \boxed{\phantom{}} \; \text{min} \]

**Explanation:**

To solve this problem, we apply the concepts of first-order kinetics. In first-order reactions, the rate depends linearly on the concentration of one reactant. The half-life \( t_{1/2} \) is calculated by using the formula:

\[ t_{1/2} = \frac{0.693}{k} \]

where \( k \) is the rate constant. To find \( k \), we use the first-order rate equation:

\[ \ln \left( \frac{[A]_0}{[A]} \right) = kt \]

Given:
- \( [A]_0 = \) initial concentration
- \( [A] = \) concentration after time \( t \)
  
After 40 minutes, 22.0% has decomposed, so 78.0% remains (100% - 22%).

\[ \ln \left( \frac{100}{78} \right) = k \times 40 \]

Calculate \( k \), and then plug the value into the half-life equation to find \( t_{1/2} \).
Transcribed Image Text:**Problem Statement:** After 40.0 minutes, 22.0% of a compound has decomposed. What is the half-life of this reaction assuming first-order kinetics? **Calculation Area:** \[ t_{1/2} = \boxed{\phantom{}} \; \text{min} \] **Explanation:** To solve this problem, we apply the concepts of first-order kinetics. In first-order reactions, the rate depends linearly on the concentration of one reactant. The half-life \( t_{1/2} \) is calculated by using the formula: \[ t_{1/2} = \frac{0.693}{k} \] where \( k \) is the rate constant. To find \( k \), we use the first-order rate equation: \[ \ln \left( \frac{[A]_0}{[A]} \right) = kt \] Given: - \( [A]_0 = \) initial concentration - \( [A] = \) concentration after time \( t \) After 40 minutes, 22.0% has decomposed, so 78.0% remains (100% - 22%). \[ \ln \left( \frac{100}{78} \right) = k \times 40 \] Calculate \( k \), and then plug the value into the half-life equation to find \( t_{1/2} \).
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