If a balanced reaction takes place in a sealed container how should the mass before the reaction begins compare to the mass after the reaction ends?

The internal energy of the system we can term it as total potential energy and kinetic energy. energy flows out of the surrounding from the system then we can say that the internal energy of the final state is lower than its initials. the sign of  δesystem is negative.δesystem = efinal - einitial=-ve  efinal  ∠einitial.

Answerh2o

Solar thermal energy and solar electric energy