M Ch. 10 (Hybridization and x A piece of silver with a ma x ezto.mheducation.com
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M Ch. 10 (Hybridization and x A piece of silver with a ma x ezto.mheducation.com /hm.tpx Chemistry 1320: Spring 2015 CHEMISTRY ridization and Delocalized Bonds) and Ch. 6 Thermochemistry v next pre Question #7 (of 10) value 20 points 1 out of 5 attempts NetCalculator Enter your answer in the provided box. Pentaborane-9 (B5H9) is a colorless, highly reactive liquid that will bur into flames when Assistance Check My Work exposed to oxygen. The reaction is Print BSH 9H3O 19 Question Help Report a Problem Calculate the kilojoules of heat released per gram of the compound reacted with oxygen. The standard enthalpy of formations of BsHo(l), B203(s), and H20(l) are 73.2,-1271.94, and 285.83 kJ/mol, respectively. kJ/g released references Hill Education. All rights reserved. Allison Mikesell save & exit b43 instructions I help submit assignment 5:49 PM 5/5/2015Explanation / Answer
Hrxn = Hf (products) - Hf (reactants)
Hrxn = [5Hf (B2O3) + 9Hf (H2O)] - [2Hf (B5H9) + 12Hf (O2)]
Hrxn = [(5)(-1271.94 kJ/mol) + (9)(-285.83 kJ/mol)] - [(2)(73.2 kJ/mol) + (l2)(0 kJ/mol)]
Hrxn = -8835.57 kJ/mol
To convert into KJ/gram:
The calculated one is the amount of heat released for every 2 moles of B5H9 reacted.
The molar mass of B5H9 is 63.12 g
Heat released per gram = (-8835.57/63.12)/2 = 69.99 KJ/gram (almost 70 KJ/g)
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