Ask Singapore Homework?
Upload a photo of a Singapore homework and someone will email you the solution for free.
Question
junior college 1 | H2 Maths
One Answer Below
Anyone can contribute an answer, even non-tutors.
h2 chem ! i need help part b :(
Date Posted: 3 years ago
Views: 435
There is a mistake in the equation. It should be 9/2 O₂ and not 8/2.
Answer will be shown shortly
Answer will be shown shortly
See 1 Answer
①In 1 mol of propene, (CH₃CH=CH₂)
number of C-H bonds to be broken = 6 mol (6 C-H bonds per molecule so 6 mol of bonds per mol of propene)
number of C=C bonds to be broken = 1 mol
number of C-C bonds to be broken = 1 mol
bond energy (C-H) = 410 kJ/mol, bond energy (C=C) = 610 kJ/mol, bond energy (C-C) = 350 kJ/mol
② In 9/2 mol of O₂, (O=O)
number of O=O bonds to be broken = 9/2 mol (for ½ mol we always consider half the bond energy) ,bond energy (O=O) = 496 kJ/mol
③ In 3 mol of CO₂ , (O=C=O)
number of C=O bonds to be formed = 6 mol, bond energy (each C=O in CO2) = 805 kJ/mol
④ In 3 mol of H₂O, (H-O-H)
number of O-H bonds to be formed = 6 mol, bond energy (O-H) = 460 kJ/mol
Enthalpy change of combustion of propene
= energy required to break bonds in the reactants - energy released from forming bonds in the products
= 6 B.E (C-H) + B.E (C=C) + B.E (C-C) + 9/2 B.E (O=O) - 6 B.E (C=O) - 6 B.E (O-H)
= 6(410 kJ/mol) + 610 kJ/mol + 350 kJ/mol + 9/2 (496 kJ/mol) - 6(805 kJ/mol) - 6(460 kJ/mol)
= -1938 kJ/mol
Do note that for the given answer they have used the value of 740 kJ/mol for B.E (C=O) instead, which results in -1548 kJ/mol ≈ -1550 kJ/mol
It might have been due to the older version of the Data Booklet used in 2004 (since its a 2004 question), which may not have distinguished between C=O of CO2 and a typical C=O from other compounds.
number of C-H bonds to be broken = 6 mol (6 C-H bonds per molecule so 6 mol of bonds per mol of propene)
number of C=C bonds to be broken = 1 mol
number of C-C bonds to be broken = 1 mol
bond energy (C-H) = 410 kJ/mol, bond energy (C=C) = 610 kJ/mol, bond energy (C-C) = 350 kJ/mol
② In 9/2 mol of O₂, (O=O)
number of O=O bonds to be broken = 9/2 mol (for ½ mol we always consider half the bond energy) ,bond energy (O=O) = 496 kJ/mol
③ In 3 mol of CO₂ , (O=C=O)
number of C=O bonds to be formed = 6 mol, bond energy (each C=O in CO2) = 805 kJ/mol
④ In 3 mol of H₂O, (H-O-H)
number of O-H bonds to be formed = 6 mol, bond energy (O-H) = 460 kJ/mol
Enthalpy change of combustion of propene
= energy required to break bonds in the reactants - energy released from forming bonds in the products
= 6 B.E (C-H) + B.E (C=C) + B.E (C-C) + 9/2 B.E (O=O) - 6 B.E (C=O) - 6 B.E (O-H)
= 6(410 kJ/mol) + 610 kJ/mol + 350 kJ/mol + 9/2 (496 kJ/mol) - 6(805 kJ/mol) - 6(460 kJ/mol)
= -1938 kJ/mol
Do note that for the given answer they have used the value of 740 kJ/mol for B.E (C=O) instead, which results in -1548 kJ/mol ≈ -1550 kJ/mol
It might have been due to the older version of the Data Booklet used in 2004 (since its a 2004 question), which may not have distinguished between C=O of CO2 and a typical C=O from other compounds.
360 Tutoring Program