Final answer:
Chemists define the potential energy as zero when charged particles are infinitely far apart with no interaction. This reference point allows the use of conservation of energy principles to describe changes as potential energy is converted to kinetic energy when particles interact.
Step-by-step explanation:
Chemists define the potential energy (PE) of a system of charged particles to be zero when the particles are infinitely far apart, leading to no interaction between them. This is a convenient choice of reference, similar to assigning the ground as zero potential energy in a gravitational potential energy problem. The conservation of energy principle is applied, stating that the mechanical energy (the sum of kinetic and potential energy) of a system remains constant if only conservative forces are present. When an electron is accelerated in a vacuum and all of the electrical potential energy is converted into kinetic energy, the initial potential energy (PEi = qV) becomes zero at the final point (PEf = 0). In essence, the internal energy of a two-charge system does not change due to the absence of external forces. Initially, the internal energy is the kinetic energy of the smaller charge, while the potential energy at a significant distance is effectively zero. This region is the reference point where potential energy is defined to be zero. Once the smaller charge starts moving towards the larger one, its kinetic energy increases as its potential energy decreases, maintaining the principle of energy conservation.