A system for modeling, simulating and analyzing chemical and biochemical reactions includes a modeling environment for constructing a model of a chemical or biochemical system comprising a plurality of chemical reactions. Each chemical reaction has a probability distribution associated therewith based on the kinetics of the particular chemical reaction. The probability distribution may be set by a user, determined automatically, or experimentally determined. The system also includes a simulation engine accepting as input said constructed model of the chemical or biochemical system and generating as output an expected result. The simulation engine calculates a reaction time for each chemical reaction based on the probability distribution associated with the particular chemical reaction. An analysis environment communicates with the simulation engine and displays the expected result.