In chemistry, the active mass of a substance refers to the concentration of that substance in a reaction. It is related to the number of particles or moles of the substance that are available to participate in a chemical reaction. The active mass is a crucial concept because it determines the rate of the reaction.
The active mass is used instead of the total mass of a substance because not all particles of a substance are available or capable of participating in a reaction. In any given sample of a substance, only a fraction of the total mass consists of particles that have the appropriate energy and orientation to react with other substances. The remaining portion may be unreactive due to factors such as the physical state (e.g., solid, liquid, or gas), molecular structure, or lack of exposure to the reactants.
When determining the rate of a chemical reaction, it is essential to consider only the particles that can actively participate in the reaction. By focusing on the active mass, chemists can accurately analyze and predict the behavior of reactants in a system. The active mass allows for a more precise understanding of the kinetics and thermodynamics of chemical reactions.
Additionally, the concept of active mass aligns with the principles of stoichiometry, where reactants combine in specific ratios. By considering only the active mass, chemists can apply stoichiometry to calculate the amount of product formed or reactant consumed accurately.
In summary, the active mass of a substance is used in chemical reactions because it represents the concentration of the substance's particles that are available and capable of reacting. The whole mass of the substance is not used because not all particles within it can actively participate in the reaction.