Zero-order

Definition

Zero-order refers to a reaction rate that is independent of the concentration of the reactants. In zero-order reactions, the rate remains constant and does not change even if the concentration of the reactant increases or decreases. This behavior typically occurs when a catalyst is involved, or when a surface reaction is taking place, where saturation has been reached.

5 Must Know Facts For Your Next Test

1. In a zero-order reaction, the rate is expressed as: Rate = k, where k is the rate constant.
2. The concentration vs. time plot for a zero-order reaction is a straight line with a negative slope.
3. Half-life for zero-order reactions is calculated using the formula: t_{1/2} = [A]_0 / (2k), indicating it is directly proportional to the initial concentration.
4. Common examples of zero-order reactions include certain enzyme-catalyzed processes and reactions occurring on solid surfaces.
5. If a zero-order reaction starts with an initial concentration of A, the concentration will decrease linearly over time until A is depleted.

Review Questions

• How does the rate of a zero-order reaction compare to that of first-order and second-order reactions?
  • The rate of a zero-order reaction is constant and does not depend on the concentration of reactants, while first-order reactions have rates that are directly proportional to the concentration of one reactant, and second-order reactions depend on either the square of one reactant's concentration or the product of two reactants' concentrations. This means that in zero-order reactions, increasing the concentration has no effect on the rate, unlike in first- and second-order reactions where changes in concentration significantly impact how quickly the reaction proceeds.
• Explain how you would determine whether a reaction follows zero-order kinetics based on experimental data.
  • To determine if a reaction follows zero-order kinetics, you would plot concentration versus time. If the plot yields a straight line with a negative slope, this indicates a zero-order process. Additionally, calculating the rate constant from experimental data should yield a consistent value regardless of changes in reactant concentrations. Comparing these results against predictions from first or second order kinetics would further confirm zero-order behavior.
• Critically assess how zero-order kinetics might impact real-world chemical processes such as drug metabolism or industrial catalysis.
  • Zero-order kinetics can significantly impact both drug metabolism and industrial catalysis by indicating that rates remain constant despite variations in substrate concentrations. In drug metabolism, this can lead to predictable elimination rates at high concentrations, but may also cause drug accumulation if dosing exceeds metabolic capacity. In industrial catalysis, understanding zero-order behavior allows for efficient design of reactors where maximum efficiency can be achieved without being limited by substrate availability. Recognizing these dynamics is crucial for optimizing processes and ensuring safety in practical applications.

Related terms

Rate constant: A coefficient that relates the reaction rate to the concentrations of reactants in a rate law, specific to each reaction and temperature.

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

Integrated rate law: An equation that relates the concentrations of reactants to time for a given reaction order, allowing for the determination of concentration at any point in time.