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 at which products are formed does not change, even as the concentration of reactants decreases. Zero-order kinetics typically occur under conditions where a reactant is saturated, such as when a catalyst is present or when one reactant is in large excess compared to others.

5 Must Know Facts For Your Next Test

1. In a zero-order reaction, the rate constant (k) has units of concentration/time, such as M/s, reflecting that the reaction proceeds at a constant rate.
2. Graphically, plotting concentration versus time for a zero-order reaction results in a straight line with a negative slope, indicating that reactant concentration decreases linearly over time.
3. Zero-order behavior can often be observed in enzymatic reactions when the enzyme is saturated with substrate, meaning adding more substrate does not increase the reaction rate.
4. The half-life of a zero-order reaction is dependent on the initial concentration and is given by the formula: t_{1/2} = [A]_{0}/(2k), where [A]_{0} is the initial concentration.
5. Common examples of zero-order reactions include certain catalytic reactions and reactions involving gas-phase reactants at high pressures.

Review Questions

• How does a zero-order reaction differ from first-order and second-order reactions in terms of concentration dependence?
  • In a zero-order reaction, the rate of reaction remains constant regardless of changes in reactant concentration, meaning it does not depend on the amount of reactant present. In contrast, first-order reactions have rates that are directly proportional to the concentration of one reactant, while second-order reactions depend on either the square of one reactant's concentration or the product of two reactants' concentrations. This key difference highlights how reaction order influences how concentrations affect reaction rates.
• Discuss the significance of the integrated rate law for zero-order reactions and how it helps in predicting reactant behavior over time.
  • The integrated rate law for zero-order reactions allows chemists to model how reactant concentrations change over time. For zero-order kinetics, this equation takes the form [A] = [A]_{0} - kt, showing a linear relationship between concentration and time. This linearity simplifies predictions about when certain amounts of reactants will be consumed, enabling better control over reaction conditions and product formation in practical applications such as pharmaceuticals or industrial processes.
• Evaluate how understanding zero-order kinetics can impact experimental design in chemical research or industrial applications.
  • Understanding zero-order kinetics is crucial for designing experiments and processes because it affects how reactants should be managed to optimize production. In scenarios where saturation occurs, researchers can control conditions to maintain zero-order behavior for consistent product formation rates. Additionally, knowing that factors like enzyme saturation or catalyst presence can lead to zero-order kinetics helps scientists tailor experiments to achieve desired outcomes while minimizing variability associated with changing concentrations.

Related terms

Rate law: An equation that relates the rate of a chemical reaction to the concentration of reactants, often expressed in the form: rate = k[A]^m[B]^n, where k is the rate constant.

Integrated rate law: A mathematical expression that relates the concentration of a reactant to time, which can be used to determine how the concentration changes over the course of a reaction.

Half-life: The time required for the concentration of a reactant to decrease by half; in zero-order reactions, half-life is directly proportional to the initial concentration.