684 words - 3 pages

The order of a reaction is the power to which the concentration of a reactant must be raised to give the experimentally observed relationship between concentration and rate

The rate of a reaction depends in part on the concentrations of the reactants. For a reaction in which reactant A forms product B in one step, you can write a simple equation.

A→B

The rate at which A forms B can be expressed as the change in A (∆A) with time, where concentration A1 is the initial concentration of A at time t1 and concentration A2 is the concentration of A at a later time, t2.

Rate= - ∆A/∆t = -concentration A2 - concentration A1 / t2-t1

Because A, the reactant, is decreasing, the concentration of A is smaller at a later time than initially and so ∆A will always be negative. The negative sign in the expression is needed to make the rate positive, as all rates must be. The rate of disappearance of A is proportional to the concentration of A.

-∆A/∆t [A]

The proportionality becomes an equation with the insertion of a constant (k).

Rate = -∆A/∆t = k x [A]

This equation, called a rate law, is an expression for the rate of a reaction on terms of the concentration of reactants. The specific rate constant (k) for a reaction is a proportionality constant relating the concentrations of reactants to the rate of the reaction. The magnitude of the specific rate constant depends on the conditions of the reaction and is determined experimentally. The value of the specific rate constant, k, is large if the products form quickly; the value is small if the products form slowly.

The order of a reaction is the power to which the concentration of a reactant must be raised to give the experimentally observed...

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