First-order reaction

Definition

A first-order reaction is a type of chemical reaction where the rate of the reaction is directly proportional to the concentration of one reactant. This means that if the concentration of that reactant changes, the rate of reaction will change in a predictable manner. Understanding first-order reactions is crucial for modeling chemical processes and predicting how quickly reactions will occur.

5 Must Know Facts For Your Next Test

1. For a first-order reaction, the units of the rate constant (k) are typically s⁻¹, indicating that it depends solely on time.
2. The concentration versus time graph for a first-order reaction is nonlinear and shows an exponential decay.
3. In first-order reactions, increasing the concentration of the reactant will result in a proportional increase in the rate of reaction.
4. The half-life of a first-order reaction is independent of the initial concentration; it remains constant throughout the reaction.
5. First-order reactions can often be identified by plotting the natural logarithm of concentration against time, resulting in a straight line.

Review Questions

• How does changing the concentration of a reactant affect the rate of a first-order reaction?
  • In a first-order reaction, the rate is directly proportional to the concentration of one reactant. This means that if you increase the concentration, the rate will increase in a predictable way, leading to faster formation of products. Conversely, if you decrease the concentration, the rate slows down accordingly. Understanding this relationship helps in controlling reaction conditions in practical applications.
• Describe how the concept of half-life applies to first-order reactions and why it is significant.
  • The half-life of a first-order reaction is significant because it remains constant regardless of initial reactant concentration. This means that no matter how much reactant you start with, it will take the same amount of time for half of it to be consumed. This property is useful for predicting how long it will take for reactions to proceed, especially in fields like pharmacology where drug metabolism often follows first-order kinetics.
• Evaluate how understanding first-order reactions can impact real-world applications in chemical engineering and pharmaceuticals.
  • Understanding first-order reactions is crucial in fields like chemical engineering and pharmaceuticals because it allows professionals to predict how substances will behave under different conditions. By applying knowledge about reaction rates and half-lives, engineers can design reactors that optimize product yield and minimize waste. In pharmaceuticals, knowing how quickly drugs metabolize can inform dosing schedules and improve patient outcomes, making it essential for developing effective therapies.

Related terms

Rate Law: An equation that relates the rate of a reaction to the concentrations of reactants, allowing for the determination of the order of a reaction.

Half-Life: The time required for the concentration of a reactant to decrease to half of its initial value, which is constant for first-order reactions.

Integrated Rate Equation: An equation that expresses the concentration of a reactant as a function of time, specifically for first-order reactions, in the form of ln[A] = -kt + ln[A]₀.