When C2H2 is burned in air, carbon dioxide and water are formed in the following

Question

When C2H2 is burned in air, carbon dioxide and water are formed in the following reaction: C2H2+O2(g)rightarrow C02(g) +H20(l) Delta ? = -1300. kJ C(s) + O2(g)Right arrow CO2(g) Delta ? = 1300. kJ H2(g) +1/2 O2(g) Rightarrow H2O(l) Delta ? = - 286. Calculate Delta for 2C(s) + H2(g) Rightarrow C2H2(g) Using the data in #14 what is the Heat of Formation of H2O(l). Delta Hf = Delta ? for melting sulfur (S) is 17. 7 kJ/mol. How many grams of sulfur can be melted by 22. 5 kJ of energy? a) 9. 8 g b) 19. 5 g c) 26. 2 g d) 40. 7 g e) 52. 5 g ·

Explanation / Answer

(14)   (i) C2H2 (g) + 5/2O2 (g) = 2CO2 (g) + H2O (l), H = - 1300 kJ

          (ii) 2C(s) + 2O2 (g) = 2CO2 (g), H = - 394 kJx2

          (iii) H2 (g) +1/2O2(g) = H2O (l) H = - 286 kJ

2C (s) + H2 (g) = C2H2 (g) H=?

By applying, Hess’s law

(ii) – (i) 2C(s) + 2O2 – C2H2(g) - 5/2O2 = - H2O(l), H = - 2*394-(-1300)= 512 kJ or (iv) 2C(s) - 1/2O2 = C2H2(g) + H2O(l), H=512 kJ

(iii) + (iv), 2C (s) + H2 (g) = C2H2 (g) H= -286 +512 kJ = 226 kJ

(15) Equation (iii) actually gives us the heat formation of water = - 286 kJ/mol

(16) H for melting of S = 17.7 kJ

So, by using 22.5 kJ energy 22.5/17.7 moles = 1.27 moles

Molar mass of S = 32g

So, 1.27 m of S = 1.27*32 g = 40.7 g. Answer is (d)

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