Zero-order

Definition

Zero-order refers to a type of reaction kinetics where the rate of reaction is constant and independent of the concentration of the reactants. This means that the reaction proceeds at a steady rate, regardless of how much reactant is present, until the reactants are depleted. In zero-order reactions, the change in concentration over time is linear, which can be represented by the equation $$[A]_t = [A]_0 - kt$$ where $$[A]_t$$ is the concentration at time $$t$$, $$[A]_0$$ is the initial concentration, and $$k$$ is the zero-order rate constant.

5 Must Know Facts For Your Next Test

1. In a zero-order reaction, the rate remains constant even if the concentration of reactants changes, which sets it apart from first-order and higher-order reactions.
2. Common examples of zero-order kinetics include certain enzyme-catalyzed reactions where substrate saturation occurs, leading to a maximum reaction rate.
3. The graph of a zero-order reaction shows a straight line when plotting concentration versus time, indicating linearity.
4. Zero-order kinetics can occur under conditions such as high substrate concentrations in enzyme reactions or when the reaction surface is saturated.
5. The units for the zero-order rate constant $$k$$ are typically mol/(L·s), which reflects how much concentration changes per unit time.

Review Questions

• How does zero-order kinetics differ from first-order kinetics in terms of concentration dependence?
  • Zero-order kinetics differs from first-order kinetics because in zero-order reactions, the rate of reaction is constant and does not depend on the concentration of reactants. In contrast, first-order reactions have rates that are proportional to the concentration of one reactant. This means that while zero-order reactions maintain a steady rate regardless of how much reactant is present, first-order reactions will slow down as reactants are consumed.
• Discuss how zero-order kinetics can be identified experimentally and what significance it has in real-world applications.
  • Zero-order kinetics can be identified experimentally by observing a linear relationship between reactant concentration and time when plotted on a graph. This means that if you measure the concentration at regular intervals and plot these values against time, you will see a straight line. This concept is significant in real-world applications like drug metabolism, where certain drugs exhibit zero-order elimination at high concentrations, influencing dosage regimens for effective treatment.
• Evaluate the implications of zero-order kinetics in enzyme-catalyzed reactions under substrate saturation conditions.
  • In enzyme-catalyzed reactions under substrate saturation conditions, zero-order kinetics imply that the enzyme's active sites are fully occupied, leading to a maximum reaction rate that does not change with increasing substrate concentration. This understanding is crucial in biochemistry and pharmacology because it helps predict how enzymes behave in various physiological conditions. Additionally, it influences drug design and therapeutic strategies by highlighting potential saturation effects that can limit drug efficacy.

Related terms

First-order: A type of reaction kinetics where the rate of reaction depends on the concentration of one reactant raised to the first power, leading to an exponential decay in concentration over time.

Rate constant (k): A specific constant that quantifies the rate of a reaction for a given set of conditions; it varies with temperature and is crucial for determining how quickly a reaction occurs.

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