Determining and comparing the heats of combustions of alcohols

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Anupma Raj-12i

May 7, 2007

WHICH ALCOHOL IS THE BEST FEUL BETWEEN METHANOL, ETHANOL AND PROPANOL?

INTRODUCTION: 

In this experiment I will determine the amount of heat energy involved in a chemical change. When an alcohol burns it produces carbon dioxide and water as products. Energy is also released in the reaction. I will be determining the amount of heat liberated when three alcohols burn, and compare their energy output, i.e. their heat of combustion. We will be using methanol CH3OH , ethanol C2H5OH , and propan-1-ol CH3CHOHCH3/C 3H 7OH.

RESEARCH QUESTION:

To investigate which alcohol gives out most energy per gram/mol/cm3 and hence, is the best fuel.

HYPOTHESIS:

I think that propan-1-ol will give out the most energy during combustion followed by ethanol and then methanol and hence, propan-1-ol will be the best fuel. During complete combustion of an alcohol, the energy is produced from formation of combustion products CO2 and H2O. Thus, Heat of Combustion should increase approximately linearly with the number of Alcohol Carbon atoms and as the formula suggests, propan-1-ol has more carbon atoms than methanol and ethanol. Therefore, it has more bonds. So more energy will be given out when these bonds are broken since there are more bonds to break.

We must also remember that the Oxygen atom in Alcohols is present with a single bond to the Carbon atom. This means Alcohols are already "partially oxidized" and some heat energy is absorbed in breaking Oxygen bonds during Alcohol combustion. However, the Heats of Formation for all the CO2 and H2O produced are much greater in magnitude than the absorbed energy related to Oxygen bonds, resulting in a net release of heat energy.

Therefore, I predict, that deciding on the basis of total energy given out per mol, propan-1-ol will be the best fuel.

VARIABLES:

INPUT VARIABLE: Different alcohols (methanol, ethanol, propan-1-ol)

OUTPUT VARIABLE: temperature of water (°C)

CONTROLLED VARIABLE: time for reaction

MATERIALS NEEDED: 

  • Alcohol samples (methanol, ethanol, and propan-1-ol) in 3 different spirit lamps
  • copper calorimeter with stirrer
  • clamp stand along with metal holder
  • electronic balance (+0.0005g )
  • 100-ml measuring cylinder (+0.5°C)
  • 100°C Thermometer (+0.5°C)
  • Distilled water
  • Stopwatch (+0.005sec)
  • Wooden board

SAFETY

  • The alcohols are highly flammable. Place the spirit lamp on a tray to contain any accidental spillage of alcohol.
  • Carefully use the cap of the alcohol lamp to smother its flame.
  • Avoid skin contact with the chemicals
  • Be careful as to not inhale vapor as it causes drowsiness.
  • WEAR EYE PROTECTION
  • Make sure room is well ventilated.

 PROCEDURE: 

1. Measure out 100 ml of water in a measuring cylinder.

2. Measure the temperature of the water.

3. Weigh the copper calorimeter.

4. Pour the measured water into the copper calorimeter.

5. Weigh the spirit lamp with the alcohol in it on your electronic balance.

6. Adjust the copper calorimeter right above the spirit lamp with your first alcohol in it with the help of the clamp stand and holders. Make sure that when you light the spirit lamp its flame will almost, but not quite, touch the calorimeter.

6. Light the spirit lamp and heat the water. Stir gently with the thermometer for 3 minutes.

8. Record the highest temperature that is reached after 3 minutes.

9. Now find the mass of the spirit lamp and alcohol on the same balance as before.

10. Carefully pour the water from the calorimeter, into the 100-ml measuring cylinder, and measure the volume. Record this volume.

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11. Repeat steps 1 to 10 once to obtain two different sets of results.

12. Repeat steps 1 to 11 with the other 2 alcohol samples.

RESULTS:

 Mass of cupper calorimeter = 186g + 0.0005g

CALCULATIONS:

METHANOL (CH 3OH):

Total Energy Change= Energy Change of Alcohol + Energy Change of Copper Calorimeter.

Energy Change of Alcohol = mass x specific heat capacity x change in temperature.                  

(Assuming change in temperature of water = change in temperature of alcohol)

Change in temperature = (16.4+15.9)/2 = 16.15°C or 16.15K     ...

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