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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Nestea on February 19, 2012, 11:35:59 PM

Title: Calculate the enthalpy of reaction (in kJ/mol) of the combustion of ethanol?
Post by: Nestea on February 19, 2012, 11:35:59 PM

Calculate the enthalpy of reaction (in kJ/mol) of the combustion of ethanol USING Hess's Law?

Here is what I have...

The balanced equation I have for ethanol is: C2H5OH(l) + 3O2(g) -> 2CO2(g) + 3H2O(g)

And from that, the three equations I have are:

C + O2 -> CO2  ... deta H = -393.5
H2 + 0.5OH -> H2O  ... deta H = -241. 8
2C + 3H2 + 0.5O2 -> C2H5OH  ... deta H = -277.7

Then I got:

(277.7) - (2 x 393.5) - (3 x 241.8) = -1234.7 kJ/mol

Is that correct? I'm not sure if the heat change's are completely right. Thank you for the help.

Edit: Also please calculate the enthalpy of reaction for one gallon of ethanol (in kJ). I am confused by this. Thank you.

Title: Re: Calculate the enthalpy of reaction (in kJ/mol) of the combustion of ethanol?
Post by: sjb on February 20, 2012, 01:58:56 AM

Quote from: Nestea on February 19, 2012, 11:35:59 PM

Calculate the enthalpy of reaction (in kJ/mol) of the combustion of ethanol USING Hess's Law?

Here is what I have...

The balanced equation I have for ethanol is: C₂H₅OH(l) + 3O₂(g)  :rarrow: 2CO₂(g) + 3H₂O(g)

And from that, the three equations I have are:

C + O₂  :rarrow: CO₂  ...  :delta: H = -393.5
H₂ + 0.5O₂ :rarrow: H₂O  ...  :delta: H = -241. 8
2C + 3H₂ + 0.5O₂ :rarrow: C2H5OH  ...  :delta: H = -277.7

Then I got:

(277.7) - (2 x 393.5) - (3 x 241.8 ) = -1234.7 kJ/mol

Is that correct? I'm not sure if the heat change's are completely right. Thank you for the help.

Edit: Also please calculate the enthalpy of reaction for one gallon of ethanol (in kJ). I am confused by this. Thank you.

Sounds about right, yes. For the second part; how many moles are there in a gallon?