Answer:
[tex]\Delta _RH=4x10^{-3}\frac{kJ}{mol}[/tex]
Explanation:
Hello,
In this case, the molar enthalpy of reaction is obtained by dividing the involved energy by the reacting moles:
[tex]\Delta _RH=\frac{12J}{3mol} =4\frac{J}{mol}[/tex]
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:
[tex]\Delta _RH=4\frac{J}{mol}*\frac{1kJ}{1000J} =4x10^{-3}\frac{kJ}{mol}[/tex]
Best regards.
