Use the following information to determine the enthalpy for the reaction shown below.

Question

CO₂(g) + 2SO₂(g) --> CS₂(l) + 3O₂(g)     ΔH^o = ?

C(graphite) + O₂(g) --> CO₂(g)            ΔH^o = −393.5 kJ

S(s) + O₂(g) --> SO₂(g)                        ΔH^o = −296.8 kJ

C(graphite) + 2S(s) --> CS₂(l)             ΔH^o = 87.9 kJ

Answer 1

Hess' Law:

CO2(g) + 2SO2(g) ==> CS2(l) + 3O2(g) ... TARGET EQUATION

Given:

(1). C(graphite) + O₂(g) --> CO₂(g)            ΔH^o = −393.5 kJ

(2). S(s) + O₂(g) --> SO₂(g)                        ΔH^o = −296.8 kJ

(3). C(graphite) + 2S(s) --> CS₂(l)             ΔH^o = 87.9 kJ

Procedure:

copy (3) to get CS₂ on right: C(graphite) + 2S(s) --> CS₂(l) ... ΔH^o = 87.9 kJ

reverse (2)x2 to get 2SO₂ on left: 2SO₂(g) --> 2S(s) + 2O₂(g) ... ΔH^o = +593.6 kJ (change sign and x2)

reverse (1) to get CO2 on left: CO₂₍g) --> C(graphite) + O₂(g) ... ΔH^o = +393.5 kJ (change sign)

Add them together to get and combine and/or cancel like terms to get...

C(graphite) + 2S(s) + 2SO₂(g) + CO₂(g) --> CS₂(l) + 2S(s) + 2O₂(g) + C(graphite) + O₂(g)

2SO₂(g) + CO₂(g) --> CS₂(l) + 3O₂(g) ... TARGET EQUATION

∆H = 87.9 + 593.6 + 393.5 = 1866 kJ