The standard heat of formation of carbon disulphide (l) given that the standard

The standard heat of formation of carbon disulphide (l) given that the standard heat of combustion of carbon(s) , sulphur(s) and carbon disulphide(l) are -393.3, -293.72 and -1108.76 kJ mol⁻¹ respectively is

Options

(a) 128.02 kJ mol⁻¹
(b) 12.802 kJ mol⁻¹
(c) -128.02 kJ mol⁻¹
(d) -12.802 kJ mol⁻¹

Correct Answer:

128.02 kJ mol⁻¹

Explanation:

(i) C(s) + O₂(g) → CO₂(g); ΔH₁ = -393.3 kJ.
(ii) S(s) + O₂(g) → SO₂(g); ΔH₂ = -293.72 kJ.
(iii) CS₂(l) + 3O₂(g) → CO₂ + 2SO₂ ; ΔH₃ = -1108.76 kJ.
On adding (i) and (ii) and subtracting (iii), we get,
C(s) + 2S(s) → CS₂(g), ΔH = -393.3 + 2 (-293.72) + 1108.76 = +128.02 kJ mol⁻¹.

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