Heat of combustion H ^ for C (s), H ₂(g) and CH ₄(g) are -94,-68 and -213 kcal mol ⁻¹ , then, H ^ for C (s)+2 H ₂(g) CH ₄(g) is:

Step-by-step solution

(i) C _ ( s ) + O _ 2( ~g ) CO _ 2(g) ; H _i=-94 kcal / mole (ii) 2 H _ 2(g) + O _ 2(g) 2 H ₂ O _ (l) ; H _ ii =-68 2 kcal / mole (iii) CH _ 4(g) +2 O _ 2(g) CO _ 2(g) +2 H ₂ O _ (l) ; H _ iii =-213 kcal / mol (iv) C _ (s) +2 H _ 2(g) CH _ 4( ~g ) ; H _ IV = ? By applying Hess's law we can compute H _ iv . aligned & H _ iv = H _ i + H _ ii - H _ iii & =(-94-68 2+213) kcal & =-17 kcal aligned