Question

A____H means that energy is ____ from a reaction.

Answer 1

Answer:

A  negative ∆H means that energy is given off  from a reaction

Explanation:

$2NO_2 (g)N_2 O_4 (g)\\\\\Delta H=-58 KJ per mol$

If the reaction has negative ∆H value then the reaction is exothermic

$N_2 O_4 (g)2NO_2 (g)\\\\\Delta H=+58 KJ per mol$

If the reaction has positive ∆H value then the reaction is endothermic

When Heat energy is given in the equation itself

If it is present on the left side it means that heat is absorbed and the reaction is Endothermic

If it is present on the right side it means heat is given off and the reaction is exothermic