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Solved: Pentaborane-9, B5H9, is a colorless, highly
Chapter 6, Problem 58P(choose chapter or problem)
Pentaborane-9, \(\text{B}_5\text{H}_9\), is a colorless, highly reactive liquid that will burst into flame when exposed to oxygen. The reaction is
\(2\text{B}_5\text{H}_9(l)+12\text{O}_2(g)\rightarrow 5\text{B}_2\text{O}_3(s)+9\text{H}_2\text{O}(l)\)
Calculate the kilojoules of heat released per gram of the compound reacted with oxygen. The standard enthalpy of formation of \(\text{B}_5\text{H}_9\) is 73.2 kJ/mol.
Questions & Answers
QUESTION:
Pentaborane-9, \(\text{B}_5\text{H}_9\), is a colorless, highly reactive liquid that will burst into flame when exposed to oxygen. The reaction is
\(2\text{B}_5\text{H}_9(l)+12\text{O}_2(g)\rightarrow 5\text{B}_2\text{O}_3(s)+9\text{H}_2\text{O}(l)\)
Calculate the kilojoules of heat released per gram of the compound reacted with oxygen. The standard enthalpy of formation of \(\text{B}_5\text{H}_9\) is 73.2 kJ/mol.
ANSWER:Step 1 of 3
Here, we are going to determine the kilojoules of heat released per gram of the compound reacted with oxygen.
The standard enthalpy change of a reaction \(\Delta H_{\text {reaction }}\), is defined as the difference between the enthalpies of the products and the enthalpies of the reactants.
\(\Delta H_{f}^{0}=\sum n \Delta H_{f}^{o}(\text { product })-\sum n \Delta H_{f}^{o}(\text { reactant }) \ldots \ldots \ldots(1)\)
Given reaction:
\(2 \mathrm{~B}_{5} \mathrm{H}_{9}(l)+12 \mathrm{O}_{2}(g) \rightarrow 5 \mathrm{~B}_{2} \mathrm{O}_{3}(\mathrm{~s})+9 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})\)
Given that,
\(\Delta H_{f}^{o}\left[H_{2} O(l)\right]=-285.8 \mathrm{~kJ} / \mathrm{mol}\)
\(\Delta H_{f}^{o}\left[\mathrm{O}_{2}(g)\right]=0\)
\(\Delta H_{f}^{o}\left(B_{5} H_{9}, l\right)=73.2 \mathrm{~kJ} / \mathrm{mol}\)
\(\Delta H_{f}^{o}\left(B_{2} \mathrm{O}_{3} \mathrm{~s}\right)=-1263.6 \mathrm{~kJ} / \mathrm{mol}\)