In an endothermic reaction what is true of the enthalpy

a) is has increased

b) is has decreased

c) it has remained uncharged

d) it has at minimum been halved

Answer is: a) is has increased.

There are two types of reaction:

1) endothermic reaction (chemical reaction that absorbs more energy than it releases).

For example, the breakdown of ozone is an endothermic process. Ozone has lower energy than molecular oxygen (O₂) and oxygen atom, so ozone need energy to break bond between oxygen atoms.

2) exothermic reaction (chemical reaction that releases more energy than it absorbs).

For example, ΔH (reaction) = - 225 kJ/mol; this is exothermic reaction.