Respuesta :
does it mean the reaction was exothermic (I am not too sure but that's what I think)
Answer:
The reaction releases 400 kJ of heat.
Explanation:
Hello,
In this case, the meaning of such -400 kJ in a reaction aims to the released energy once the chemical reaction goes to completion, it means that -400 kJ are realsed in form of heat, therefore, the products have 400 kJ less energy than the rectants, considering the attached picture.
Best regards.