Question

Given that ΔH^o for the thermochemical equation

2 SO₂(g) + O₂(g) → 2SO₃(g)

is – 198 kJ, what is the enthalpy change for the decomposition of 1 mole of SO₃ to give O₂ and SO₂, all in the gas state?

Method: Write down the equation of the reaction required (decomposition of SO₃ to give O₂ and SO₂):
SO₃(g) → SO₂(g) + ½O₂(g)
Compare this equation with the one for which the thermodynamic information is available, and decide what operations are necessary to make them identical.
If you reverse a reaction, you must change the sign of ΔH^o.
If you multiply a reaction through by a factor, you must multiply ΔH^o by that factor also.

Select one:

a. + 99 kJ

b. - 99 kJ

c. - 198 kJ

d. + 198 kJ

e. 0 kJ