Question

calculate the enthalpy change when 4.00 mol Cl2O7 is produced according to the following balanced equation:
2Cl2(g) + 7O2(g) + 130kcal -> 2Cl2O7(g)
a. 1040 kcal
b. -260 kcal
c. 260 kcal
d. -1040 kcal

** if you could explain it as well, that would be much appreciated !! if not, thats okay too its multiple choice

Answer 1

So the equation is,

2Cl2(g) + 7O2(g) + 130kcal -> 2Cl2O7(g)

from this , ΔH°rxn=$130kcal.mol^{-1}$

$mol^{-1}$ is mentioned because it is for per mole of reaction. So for 4. moles of the product $2Cl_{2} O_{7}$ we need 4/2 moles of reaction to be used to calculate associated enthalphy change for the reaction.

Therefore$4/2*130=260 kcal$