Saved Bookmarks
| 1. |
The thermochemical equation for solid and liquid rocket fuel are given below : 2Al (s) +1 1/2 O2 (g) →Al2 O3 s ;ΔH= -1667.8 kJ mol-1H2(g) +1/2 O2(g) →H2O(l);ΔH= -285.9 kJ mol-1(a) If equal masses of aluminium and hydrogen are used, which is a better rocket fuel ? (b) Determine ΔH for the reaction :Al2O3(s) 2Al (s) +1 1/2 O2 (g). |
|
Answer» (a) From the first given equation, 2 moles of Al (i.e., 2 × 27 g = 54 g) on combustion give heat = 1667.8 kJ ∴1 g of Al on combustion gives heat = (1667.8/54) = 30.9 kJ From the second given equation, 1 mole of H2 (= 2g) on combsution gives heat = 285.9 kJ ∴1 g of H2 on combustion gives heat = (285.9/2) = 142.95 kJ Thus, H2 is a better rocket fuel. (b) Writing the reverse of the first reaction, we have Al2O3 (s)→ 2Al (s)+ 1 1/2 O2 ΔH= +1667.8 kJ mol-1 Thus, for the reaction given in part (b) of the problem, ΔH = + 1667.8 kJ mol–1 |
|