If 3 moles of a compound use 12 J of energy in a reaction, what is the Hreaction in kJ/mol

Explanation:

Hello,

In this case, the molar enthalpy of reaction is obtained by dividing the involved energy by the reacting moles:

Thus, it is important to notice that the compound "uses" the energy, it means that it absorbs the energy, for that reason the sign is positive. Moreover, computing the result in kJ/mol we finally obtain:

Best regards.

on ap ex the answer would be 0.004 kJ/mol

pure substance: iron,copper

impure substance: water,charcoal