The thermochemical equations for solid and liquid rocket fuels are given below : (i) 2AI(s) 3/2O_(2)(g) to AI_(2)O_(3)(s), DeltaH = -1667.8 kJ (ii)H_(2)(g) + 1/2O_(2)(g) to H_(2)O(l), DeltaH = -285.9 kJ (a) If equal masses of aluminium and hydrogen are used, which is better rocket fuel? (b) Determine DeltaH for the reaction, AI_(2)O_(3)(s) to 2AI(s) + 3/2 O_(2)(g).

The thermochemical equations for solid and liquid rocket fuels are giv

1.	The thermochemical equations for solid and liquid rocket fuels are given below : (i) 2AI(s) 3/2O_(2)(g) to AI_(2)O_(3)(s), DeltaH = -1667.8 kJ (ii)H_(2)(g) + 1/2O_(2)(g) to H_(2)O(l), DeltaH = -285.9 kJ (a) If equal masses of aluminium and hydrogen are used, which is better rocket fuel? (b) Determine DeltaH for the reaction, AI_(2)O_(3)(s) to 2AI(s) + 3/2 O_(2)(g).
Answer» Solution :According to reaction (i) `2AI (s) + 3/2O_(2)(g) to AI_(2)O_(3)(s)DeltaH = -1667.8 kJ` Heat evolved in the combustion of `(2 XX 27) 54` g ofAI = 1667.8 kJ. According to reaction(ii) `H_(2)(g) + 1/2O_(2)(g) to H_(2)O(l) DeltaH = -285.9 kJ` Heat evolved in the combustion of 2 g of hydrogen = 285.9 k.J MAKIN equal masses, (a)Heat evolved in the combustion of 54 g of hydrogen ` = (285.9 xx 54)/(2) = 7719.3 kJ`. `therefore` Hydrogen is a better rocket fuel because heat evolvedfrom 54 g of`H_(2)` is more than that `DeltaH` for the reaction: `AI_(2)O_(3)(s) to 2AI(s) + 3/2 O_(2)(g) DeltaH = `? This is the reverse of equation (i). Therefore, `DeltaH` for this reaction is `DeltaH = + 1667.8 kJ`.