Half Life

Concept: Chemistry (Chemical Kinetics) - Half-life of First Order Reactions.

Step 1: Identify the given value. Rate constant ( ) = .

Step 2: State the formula for half-life. For a first-order reaction, the half-life ( ) is calculated using: $ $

Concept: Chemistry (Chemical Kinetics) - First Order Reaction Dynamics.

Step 1: Calculate the rate constant ( ). For a first-order reaction, the relationship between half-life ( ) and the rate constant is . Given hours: .

Step 2: Define the initial and final concentrations. Let the initial concentration be 100. The question states that 60% of the reactant "disappears". This means 60% has reacted. The remaining concentration .

Step 3: Set up the first-order integrated rate equation. The formula to find the time ( ) is: .

Step 4: Substitute the values into the equation. . Simplify the log term: . Using standard log tables, .

Step 5: Calculate the final time. hours. This value matches option A. $ $