A new concept for the representation of knowledge about dynamic systems in the context of reasoning about actions and change is introduced. It is based on the equational logic programming approach, which has proven to be an adequate foundation for representing knowledge for planning problems. The basic new idea is the reification of both actions and facts, allowing them to be handled as resources which can be produced and consumed during the planning process. The concept uses a chemical metaphor in which situations are represented as solutions in which floating molecules can interact freely according to interaction rules. Situations can be stratified by encapsulating subsituations within membranes such that reactions can occur locally. The membrane mechanism enables us to deal with abstraction and hierarchical planning. Using a simple example, we illustrate step by step how conventional, as well as hierarchical, planning problems can be solved with the new concept. As a concrete deductive approach to reasoning about actions, we show that and how the equational logic programming approach can be extended to the new concepts. We also show that this approach coupled with the new concept can be mapped onto an extended version of the Chemical Abstract Machine. As this machine is a model for parallel processes this may lead to a parallel computational model for reasoning about situations, actions, and causality.