write a balanced equation for the combustion of gasesous methanol and use bond e
ID: 839045 • Letter: W
Question
write a balanced equation for the combustion of gasesous methanol and use bond energies to calculate the enthalpy of combustion of methanol in kJ/mol (CH3OH)
I did the balanced equation and the calculation and i god 1175 kj/mol but the answer wasd 641kj/mol. i attached how i did it. let me know in which step i got wrong
CH3OH + 2-3 O2 rightarrow CO2 + 2H2O C - H = 414 C - O = 360 O - H = 464 O - O = 142 C - O = 799 H - O = 434 H-C-H-H - - O - H 3(414) + 360 + 464 3/2 (142) (C-H) (C-O) (O-H) 0-0) -2(799) - 4(464) (C - O) (H - O) = - 1175KJExplanation / Answer
Well bond breaking requires energy while bond making releases energy. Look up the bond energy and mean bond energy for the bonds in the reactants and products.
Consider the reaction
CH4 + 2O2 ---> CO2 + 2H2O
Bond breaking (endothermic)
Each mole of CH4 has 4 moles of C-H bond. So look up the mean bond energy for C-H bonds and multiply the value by 4.
Each mole of O2 has 1 mole of O=O bonds. 2 moles O2 has 2 moles of O=O bonds. Look up the bond enthalpy value for O=O and double it.
Add the values for these two bond breaking steps together to give the total energy needed.
Bond making (exothermic)
Each mole CO2 has 2 moles of C=O bonds in it (O=C=O). Use the C=O energy and double it.
Each mole H2O has 2 moles of O-H bonds. 2 moles H2O has 4 moles of O-H. Lookup the O-H energy and multiply it by 4.
Add these values together.
Now the energy for the overall reaction is the difference between what you put in and what you get back. As this reaction is exothermic, you must get more back than you put it. So subtract the values and you have the value.
You need to apply this to your reaction.
Hint
CH3OH has 3 moles of C-H bonds, 1 mole of C-O bonds and 1 mole of O-H bonds.
1.5 moles O2 has 1.5 moles of O=O bonds
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