Investigate and compare the amount of energy released during the combustion of alcohols with practical and theoretical combustions.

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Chemistry Coursework                                        

Objective

My aim is to investigate and compare the amount of energy released during the combustion of alcohols with practical and theoretical combustions. Combustion (burning) is the reaction of substance with oxygen.

I aimed to use four different alcohols, these being:

  • Ethanol
  • Butanol
  • Proponol
  • Methanol

Method

I set up the apparatus as the diagram shows:

To start the experiment I weighed the empty burner using electronic scales, and then added 75ml of the alcohol I was using, and then weighed it again. I then calculated the mass of alcohol in the burner. I then took the temperature of the water, and then lit the burner. I decided to keep the experiment running each time until the water had risen 200c. when this had happened I blew out the burner, and re-weighed it, so that I could calculate how much alcohol had been burned.

At this point I used the formula:

Energy = Mass of Water x Temperature Rise x Specific heat Capacity

                (g)                (0C)

To calculate the practical results for change in chemical energy I had to first convert the amount of alcohol type burnt into KJ/mol. This was done using the following formula:

Amount of energy given off [Energy]

___________________________________ x     number of grams per mol

Amount Burned (g)

I was given the following bond values as below:

Results

Ethanol

C2H5OH                         +               3O2                                          2CO2    +    3H2O

       H    H                        O=O                        O            H-O-H        

        |      |                                                ||

H – C – C – O – H                O=O                        C=O            H-O-H        

        |      |                                                O

       H    H                        O=O                        ||            H-O-H        

                                                        C=O

Theoretical

H-C x5 = (412x5)        O=O  x3                                O=C x4                H-O x 6

C-C x1 = 348                (496 x 3)                                +                

O-C x1 = 360                -------------                        (743 x4)                (463 x6)

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O-H x1 = 463                   1488                                ----------                -----------

        --------                                                2972                2778

        3231

4719                                                        5750

4719 – 5750 = -1031

Practical

50g x 200 x 4.2                        92000

-------------------        x 46  =                 ---------                  = 92

  1. 1000

50g x 290 x 4.2                        114811.4754

--------------------        x 46  =                -----------------        = 114.8114754

  1. 1000

Butanol

C4H9OH                         +               6O2                                          4CO2    ...

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