Given the following thermo chemical equations 

(i) S(rhombic) + O2(g) -----> SO2(g), ∆H = - 297.5 kj mol-1 

(ii) S(monoclinic) + O2 ------> SO2(g),∆H = - 300.0 kj mol-1 

Calculate ∆H for the transformation of one gram atom of rhombic sulphur into monoclinic sulphur.

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1 Answers

 Required equation 

S(rhombic) ------> S(monoclinic), ∆H = ? 

Subtract equation (ii) from (i) it gives 

S(rhombic) – S(monoclinic) ----> 0, ∆H =297.5 – (-300.0) = 2.5 KJmol-1 

                   OR 

S(rhombic)------> S(monoclinic), ∆H = +2.5 kj mol-1 

Thus for the transformation of one gram atom of rhombic sulphur into monoclinic sulphur, 2.5 kj mol-1 of heat is absorbed.

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