T1/2 = 0.693/k

Definition

The equation t1/2 = 0.693/k defines the half-life of a reaction, which is the time required for the concentration of a reactant to decrease to half of its initial value. This relationship connects the half-life directly to the rate constant (k) of a first-order reaction, illustrating how the speed of a reaction influences how quickly it proceeds.

5 Must Know Facts For Your Next Test

1. The half-life equation applies specifically to first-order reactions, where the concentration decreases exponentially over time.
2. For first-order reactions, the half-life is independent of the initial concentration, meaning it remains constant regardless of how much reactant you start with.
3. In the equation, 0.693 represents the natural logarithm of 2, which is essential for calculating half-life from the rate constant.
4. As the rate constant (k) increases, the half-life (t1/2) decreases, meaning reactions with higher rates will reach half their initial concentration more quickly.
5. The concept of half-life is crucial in various fields such as pharmacology and nuclear chemistry, where understanding decay rates impacts drug dosage and radioactive decay.

Review Questions

• How does the relationship between half-life and rate constant affect the behavior of first-order reactions?
  • The relationship defined by t1/2 = 0.693/k shows that for first-order reactions, as the rate constant (k) increases, the half-life (t1/2) decreases. This means that reactions with higher rates will take less time to reduce their concentration by half. Understanding this relationship helps predict how quickly a substance will react or decay over time.
• What role does the value 0.693 play in the half-life equation and why is it significant?
  • The value 0.693 in the equation t1/2 = 0.693/k represents the natural logarithm of 2, which is crucial for converting between the rate constant and the time it takes for a substance to reach half its initial concentration. This significance lies in its ability to simplify calculations related to exponential decay processes, making it easier to understand how quickly first-order reactions occur.
• Evaluate how understanding the concept of half-life can influence practical applications in fields like pharmacology or environmental science.
  • Understanding half-life allows professionals in pharmacology to determine appropriate dosing schedules for medications based on how quickly drugs are metabolized in the body. In environmental science, knowledge of half-lives helps assess how long pollutants will remain active in ecosystems, guiding cleanup efforts and regulatory measures. This comprehension not only aids in making informed decisions but also fosters effective strategies for managing substances over time.

Related terms

First-Order Reaction: A type of chemical reaction where the rate is directly proportional to the concentration of one reactant.

Rate Constant (k): A proportionality constant that relates the rate of a reaction to the concentrations of reactants, specific to each reaction at a given temperature.

Exponential Decay: A process where a quantity decreases at a rate proportional to its current value, often characterized by a constant half-life.