In a mass balance, what is necessary for total mass changes?

For total mass changes in a mass balance, it is essential that the inputs and outputs must be equal to ensure that the system is in a steady state. In a mass balance, the principle relies on the conservation of mass, which states that mass cannot be created or destroyed in a closed system. Therefore, the total mass entering the system must equal the total mass leaving the system, plus any accumulation or depletion of mass inside the system over time.

When inputs and outputs are balanced, it indicates that the system is stable, and any change in mass can be accounted for by observing how much mass is being added or removed. This relationship is crucial in various applications, such as chemical processes, environmental studies, and manufacturing, where maintaining mass balance is necessary for efficiency and safety.

Other options do not align with the fundamental principles of mass balance. Monitoring only outputs disregards the inputs that might be contributing to changes in total mass. Neglecting accumulation would fail to account for transient changes within the system, and stating that mass can be created or destroyed contradicts the core concept of mass conservation. Thus, the recognition that inputs and outputs must be equal is pivotal for accurate mass balance analysis.