Question

S(rhombic)+O2(g)--->SO2(g)
change in H(rxn)= -296.06 kJ/mol

S(monoclinic)+O2(g)--->SO2(g)
change in H(rxn)= -296.36 kJ/mol

1. Calculate the enthalpy change for the transformation. S(rhombic)-->S(monoclinic)

Our goal is to calculate the enthalpy change for the formation of monoclinic sulfur from the rhombic sulfur. To do soo, we must arrange the equations that are given in the problem in such a way that they will sum to the desired overall equation.

So which equation should be reversed: 1st or 2nd?

What is the sign of change in H for the reversed equation: positive or negative?

Answer 1

Use equation 1 as is.
Reverse equation 2 (changer sign, too) and add to equations. Add delta Hs.
Cancel ions common to each side. You should have
S(rhombic) ==> S(monoclinic)

Answer 2

Thank you so much