Question

The standard heat of combustion of $Alis-837.8kJmo{l}^{-1}at{25}^{\circ }C$. If $Alreactswith{O}_{2}at{25}^{\circ }C$, which of the following release $250kJ$ of heat?

• A. the reaction of $0.624molofAl$
• B. the formation of $0.624molofA{l}_2{O}_3$
• C. the reaction of $0.312molofAl$
• D. the formation of $0.150molofA{l}_2{O}_3$

Answer 1

The correct option is D the formation of $0.150molofA{l}_2{O}_3$

$Al+\frac{3}{2}{O}_2\to \frac{1}{2}A{l}_2{O}_3$
$\stackrel{27g}{\Delta H}=\stackrel{51g}{-837.8kJmo{l}^{-1}}$
a) 0.624 mol of $Al=837.8\times 0.624$ on combustion gave $=523kJ$.
Hence, false.
b) Formation of 0.624 mol of $A{l}_2{O}_{3}gave=837.8\times 2\times 0.624=1045kJ$
Hence, false.
c) 0.312 mol of Al on combustion gave = 261 kJ
Hence, false.
d) Formation of 0.150 mol of $A{l}_2{O}_{3}gave=251.3kJ$
Hence, true.