Chemical Reaction Orders

Chemical reactions can be classified based on their reaction kinetics. The general reaction form is:

aA + bB --> cC + dD

Reactions are categorized as zero-order, first-order, second-order, or mixed-order (higher-order) reactions.

1. Zero-Order Reactions

   Zero-order reactions (order = 0) have a constant rate. This rate is independent of the concentration of the reactants. The rate law is:

   rate = k, with k having the units of M/sec.

2. First-Order Reactions

   A first order reaction (order = 1) has a rate proportional to the concentration of one of the reactants. A common example of a first-order reaction is the phenomenon of radioactive decay. The rate law is:

   rate = k[A] (or B instead of A), with k having the units of sec^-1

3. Second-Order Reactions

   A second-order reaction (order = 2) has a rate proportional to the concentration of the square of a single reactant or the product of the concentration of two reactants:

   rate = k[A]² (or substitute B for A or k multiplied by the concentration of A times the concentration of B), with the units of the rate constant M^-1sec^-1

4. Mixed-Order or Higher-Order Reactions

   Mixed-order reactions have a fractional order for their rate:

   e.g., rate = k[A]^1/3

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