Lecture 5

Flashcards based on lecture notes covering reaction rates, rate laws, and reaction orders.

Rate Law (Differential Rate Law)

A mathematical equation that expresses the relationship between the rate of a reaction and the concentration of reactant (and, in rare cases, the concentration of product).

Rate Law Determination

Must be experimentally determined.

Reaction Order and Balanced Coefficients

The order of the reactants in a rate law CANNOT be established from the balanced coefficients, except when dealing with elementary reactions of a reaction mechanism.

General form of the rate law (A → products)

rate = k [A]^n

k

Rate constant for the reaction.

[A]^n

The molar concentration of A raised to some power, n.

n

The order of the reactant.

Reaction Order

reflects the rate’s sensitivity to changing that reactant’s concentration

Rate Constant (k)

depends on the specific reaction and the temperature

Zero-Order Reaction

Reaction rate is constant as the reaction proceeds.

First-Order Reaction

The rate is directly proportional to the reactant concentration.

Second-Order Reaction

The rate is directly proportional to the square of the reactant concentration.

Method of Initial Rates

measure the initial rate of a reaction under a set of initial concentrations for the reactant(s); change the initial concentration of only one reactant (keeping the concentrations of the other reactants constant) and measure the initial rate under the new conditions; establish the order with respect to only that one reactant; repeat for all other reactants; calculate the value of the rate constant.