The following diagrams represent mixtures of NO(g) and O21g2. These two substances react as follows: 2 NO1g2 + O21g2¡2 NO21g2 It has been determined experimentally that the rate is second order in NO and first order in O2. Based on this fact, which of the following mixtures will have the fastest initial rate? [Section 14.3]

Key Concepts

Rate Law

The rate law expresses the relationship between the rate of a chemical reaction and the concentration of its reactants. It is determined experimentally and indicates how the rate depends on the concentration of each reactant raised to a power, which corresponds to its order in the reaction. For the given reaction, the rate law is rate = k[NO]^2[O2]^1, showing that the reaction is second order in NO and first order in O2.

Reaction Order

Reaction order refers to the exponent of a reactant's concentration in the rate law, indicating how the rate of reaction changes with varying concentrations. A second-order reaction in a reactant means that doubling its concentration will quadruple the reaction rate, while a first-order reaction means that doubling the concentration will double the rate. Understanding the order helps predict how different mixtures will affect the initial reaction rate.

Initial Rate of Reaction

The initial rate of reaction is the speed at which reactants are converted to products at the very beginning of the reaction, typically measured right after the reactants are mixed. It is influenced by the concentrations of the reactants and their respective orders in the rate law. To determine which mixture has the fastest initial rate, one must calculate the rate using the concentrations of NO and O2 in each mixture according to the established rate law.