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The thermochemical equation for solid and liquid rocaket fuel are given below 2Al(s) + 1(1)/(2)O_(g) rarr Al_(2)O_(3)(s) , Delta H = - 1667.8 kJ mol^(-1) H_(2)(g) + (1)/(2) O_(2)(g) rarr H_(2)O(l) , Delta H = - 285.9 kJ mol^(-1) (a) If equal masses fo aluminiumand hydrogen are used, which is a better rocket fuel? (b ) Determine Delta H for the reaction : Al_(2)O_(3)(s)rarr 2Al(s) + 1(1)/(2)O_(2)(g) |
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Answer» Solution :(a) From the first given equation. 2 moles of Al `( i.e., 2 xx 27 g = 54G)` on combustion GIVE heat `= 1667.8 KJ` `:. 1 g` of Al combustion givesheat ` = (1667.8 ) / ( 54) = 30.9kJ` From the second given equation, 1 mole of `H_(2)( = 2g) ` on combustion gives heat `= 285.9 kJ` `:.` 1 g of `H_(2)` on combustion gives heat `= (285.9) /( 2) = 142.95kJ` Thus, `H_(2)` is a better rocket fuel. (b) Writing the reverse of the first REACTION, we have `Al_(2)O_(3)(s) rarr2Al(s) +1(1)/(2) O_(2)(g), DeltaH = + 1667.8 kJ mol^(-1)` Thus, for the reaction given in part (b) of the problem, `Delta H = + 1667.8 kJ mol^(-1)` |
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