First-order

Definition

First-order refers to a type of reaction kinetics where the rate of reaction is directly proportional to the concentration of one reactant. In first-order reactions, as the concentration of that reactant decreases, the rate also decreases linearly, following a specific mathematical relationship. This concept is essential in understanding how different reactants influence the overall speed of chemical reactions and is often expressed in rate laws.

5 Must Know Facts For Your Next Test

1. For a first-order reaction, the unit of the rate constant (k) is s^{-1}, indicating that it has a time dimension.
2. The integrated rate law for a first-order reaction is given by the equation: ln([A]_0/[A]) = kt, where [A]_0 is the initial concentration and [A] is the concentration at time t.
3. Graphing ln([A]) versus time produces a straight line with a slope of -k for first-order reactions, making it easier to determine the rate constant.
4. In a first-order reaction, doubling the concentration of the reactant results in doubling the reaction rate, highlighting its direct proportionality.
5. First-order kinetics are commonly observed in radioactive decay processes and some enzyme-catalyzed reactions, showcasing their widespread relevance.

Review Questions

• How does the concentration of a reactant in a first-order reaction affect the rate of that reaction?
  • In a first-order reaction, the rate is directly proportional to the concentration of one specific reactant. This means that if the concentration of that reactant increases, the rate of the reaction will also increase at a consistent ratio. Conversely, as the concentration decreases, the rate diminishes accordingly. This linear relationship allows chemists to predict how changes in concentration will impact overall reaction rates.
• Explain how you can determine if a reaction follows first-order kinetics using experimental data.
  • To determine if a reaction follows first-order kinetics, you can analyze experimental data by plotting ln([A]) versus time. If this plot results in a straight line, it indicates that the reaction is indeed first-order, as per its integrated rate law. The slope of this line will provide you with the negative value of the rate constant (k), confirming both the order and kinetics of the reaction.
• Evaluate the importance of first-order kinetics in real-world applications such as pharmaceuticals or environmental science.
  • First-order kinetics plays a crucial role in various real-world applications, especially in pharmaceuticals where drug elimination from the body often follows first-order principles. Understanding this behavior allows for accurate dosing regimens based on half-life calculations. Similarly, in environmental science, first-order reactions help model pollutant degradation rates and predict how long contaminants may persist in ecosystems, impacting strategies for pollution management and remediation efforts.

Related terms

Rate Law: An equation that relates the rate of a reaction to the concentration of its reactants, providing insight into the order and nature of the reaction.

Half-life: The time required for half of the reactant to be consumed or converted in a reaction, which remains constant for first-order reactions regardless of initial concentration.

Integrated Rate Law: A mathematical expression that describes how the concentration of reactants changes over time for a specific order of reaction, allowing for predictions about reaction progress.