dimethyle chemical composition: C2H60. (Chemists call these structural isomers -
ID: 1086368 • Letter: D
Question
dimethyle chemical composition: C2H60. (Chemists call these structural isomers -molecules with the same composition, but different connectivity of atoms.) Determine the energy released in the combustion of dimethyl ether. Average Bond Energies (k]/mol) C-N 29:3 C-0 358 C-C 347 C-H 414 N-0 201 N-H 389 N-N 163 0-0 142 0-H 464 H-H 436 C-C 614 C-N 615 C-0 799 N-N 418 N=0 607 0-0 498 C C 839 N=N 941 b. Which fuel releases more energy per mole - ethanol (from the first page) or dimethyl ether? 6. Of the three bonds labelled X, Y, and Z in acetic acid at right: - Which is the shortest? Why? - Which is the weakest? Why?Explanation / Answer
5. Balanced equation,
CH3OCH3 + 3O2 --> 2CO2 + 3H2O
a. using bond energies,
dHrxn = dH(reactants) - dH(products)
= (6 x 414 + 2 x 358) + (3 x 498) - (2 x 2 x 799 + 3 x 2 x 464)
= -1286 kJ/mol
Energy released -1286 kJ/mol
b. Energy released in ethanol combustion,
dHrxn = dH(reactants) - dH(products)
= (5 x 414 + 1 x 358 + 1 x 464) + (3 x 498) - (2 x 2 x 799 + 3 x 2 x 464)
= -1594 kJ/mol
Ethanol (fuel) releases more heat per mole than dimethylether (fuel).
6. Of the three bonds labelled X, Y and Z in acetic acid,
- the shortest one is C=O with a sigma and a pi-bond. two bonds together makes this bond the shortest of all the other single bonds.
- Weakest bond is O-H, as oxygen pulls shared electron towards itself making H electropositive and readily ionizable.
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