What characterizes heterogeneous reactions?

Heterogeneous reactions are characterized by the presence of reactants in at least two different phases, which could include combinations of solids, liquids, and gases. This distinction is significant because the phase of the reactants affects how the reaction occurs and its rate. For example, in a heterogeneous catalysis scenario, a solid catalyst interacts with gaseous or liquid reactants, leading to a reaction that is influenced by the surface area of the solid and the concentration of the reactants in the other phases.

This contrasts with homogeneous reactions, where all reactants are in the same phase, allowing for more uniform interaction among the molecules. The differentiation between phases plays a crucial role in reaction dynamics, kinetics, and the pathways through which reactions proceed, making this aspect fundamental for understanding various chemical processes, particularly in industrial applications.

The other options misrepresent the nature of heterogeneous reactions. Reactions that occur in a single phase refer to homogeneous reactions, while focusing solely on gases does not encompass the wider range of phase interactions present in heterogeneous systems. Furthermore, the concept of a reaction involving only one reactant does not align with the definition of heterogeneous reactions, which typically involve multiple substances interacting across different phases.