Zero-order reaction

Definition

A zero-order reaction is a type of chemical reaction where the rate of reaction is constant and independent of the concentration of the reactants. This means that the rate remains the same regardless of how much reactant is present, leading to a linear decrease in concentration over time. Zero-order reactions often occur under specific conditions, such as when a catalyst is saturated or when a surface reaction takes place.

5 Must Know Facts For Your Next Test

1. In zero-order reactions, the rate of reaction does not change as the concentration of reactants decreases; it remains constant over time.
2. The mathematical expression for a zero-order reaction can be represented as $$[A] = [A]_0 - kt$$, where $$[A]$$ is the concentration at time $$t$$, $$[A]_0$$ is the initial concentration, and $$k$$ is the rate constant.
3. Zero-order reactions often occur in enzyme-catalyzed reactions when all active sites are occupied, leading to saturation.
4. The units of the rate constant $$k$$ for a zero-order reaction are typically mol/(L·s), indicating its dependence on concentration and time.
5. In terms of half-life, for zero-order reactions, it can be expressed as $$t_{1/2} = [A]_0/(2k)$$, showing that as initial concentration increases, the half-life also increases.

Review Questions

• How does a zero-order reaction differ from first-order and second-order reactions in terms of rate dependence on reactant concentration?
  • A zero-order reaction has a constant rate that does not depend on the concentration of reactants, while first-order and second-order reactions have rates that vary with changes in reactant concentrations. In first-order reactions, the rate is directly proportional to the concentration of one reactant, whereas in second-order reactions, it can be proportional to either one or two reactants. This fundamental difference leads to distinct kinetics and graphs when analyzing the concentration versus time plots for each type.
• Explain how a zero-order reaction can be influenced by environmental factors such as temperature and pressure.
  • While zero-order reactions maintain a constant rate regardless of reactant concentrations, they can still be influenced by external factors like temperature and pressure. An increase in temperature typically accelerates chemical reactions due to higher kinetic energy, potentially increasing the rate constant $$k$$. Similarly, changes in pressure may affect gaseous reactants and their behavior at high concentrations. However, within those specific conditions that define zero-order behavior, any changes will still show that the rate remains constant despite fluctuations in reactant levels.
• Discuss how understanding zero-order reactions can be applied in real-world scenarios such as drug release or catalytic processes.
  • Understanding zero-order reactions is crucial in fields like pharmacology and catalysis. In drug release systems, zero-order kinetics can ensure a steady release rate over time, which leads to more predictable therapeutic effects. This is especially important for sustained-release formulations where maintaining consistent drug levels is essential for efficacy. Similarly, in catalytic processes, recognizing when a system behaves as a zero-order reaction allows chemists to optimize conditions for maximum efficiency by preventing saturation and ensuring that catalysts operate effectively without being overwhelmed by substrate concentrations.

Related terms

Rate constant: A proportionality factor in the rate equation that relates the rate of reaction to the concentration of reactants; for zero-order reactions, it indicates the constant rate.

Half-life: The time required for the concentration of a reactant to decrease to half of its initial value; in zero-order reactions, this half-life depends on the initial concentration.

Pseudo-zero-order reaction: A reaction that behaves like a zero-order reaction under certain conditions, typically when one reactant is in large excess compared to others.