How can you be sure a chemical reaction is happening? 1. a solid dissolves
2. a new substance is formed
3. water turns into steam
4. a mixture is made ​

Answerspecies;

H tricky one let me think and get back to u

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.