[arbitrandomuser]

The bond energy is also mass . Energy is mass , If you had a nuclear reactor surrounded by gas and this setup ran a turbine which compressed a humungous spring and this whole setup was completely sealed and sits on a gigantic weighing scale. You run the nuclear reactor, the spring compresses gaining potential energy, waste heat goes into the gas molecules as kinetic energy. As the reactor progresses converting "mass to energy" does the weighing scale become lighter ?

[deepsun]

Well, weighing scale doesn't measure mass, it measures weight. It's just scales' UI converts it to kg/lb for usability, instead of showing N it actually measures (weight is a force, and force is measured in newtons).