THE LINK BETWEEN CARBON ATOMS IN A FUEL AND THE ENERGY IT RELEASES.

ENAJITE JASMNIE AGESE 02/05/2007 PAGE

CHEMISTRY COURSEWORK

PLANNING

INTRODUCTION

Alcohols generally belong to compounds whose molecules are based on chains of carbon atoms. They usually contain one oxygen atom, which is joined to a carbon atom by a singular bond. This makes them different to other compounds. The oxygen atom is joined to the hydrogen atom as well as the carbon atom, which makes the oxygen a part of a hydroxyl group. These atoms are generally a part of a hydrocarbon chain. These alcohols can take away water from the body, in which a hydrocarbon chain has replaced a hydrogen atom. Alcohols have a general structure of CnH2n+1OH

The aim of this investigation is to see the link between the numbers of carbon atom in a fuel with the amount of energy it releases. There would be a change in the amount of energy given off that is getting greater, the more carbon atoms in the fuel, the more there are more bonds to be broken and formed, thus producing more energy. ‘In a chemical reaction, bonds in the reactant molecule are broken and new ones are formed. Atoms are rearranged. Energy has to be put in to break bonds, and energy is given out when bonds are formed.’ When the total energy put in is greater than the energy put out, the substance cools down (it is endothermic). This is expressed as Δ +ve (delta positive). If the total energy put in is less than the energy created, then the substance warms up (it is exothermic). This is expressed as Δ -ve (delta negative).

I will investigate eight different alcohols using an alcohol or spirit burner, to measure the energy change during burning them by measuring the change in temperature of some water held by a container. This container must have a value of specific heat capacity so I could calculate heat transferred to it as well. Probably the most conductive container available for use in the classroom is a calorimeter. As well as not wasting energy in the heating of the container, I could also try to stop heat from escaping the top and edges of the container by covering it with a fitting lid. I will try to prevent the wind from blowing the flames to a different direction so all the windows must be shut.

HYPOTHESIS

More energy is released as more bonds are formed, below is the list of approximate energy required to break and form all bond involved in burning alcohols

TYPE OF BOND ENERGY REQUIRED TO BREAK THE BOND (j)
C-H 412
C-O 360
O-H 463
C-C 348

O-O 496

C=O 743

Below is the calculation of all the alcohols I have decided to use. They are as follows:

Methanol has three C-H bonds, one C-O bond and one O-H bond therefore the calculation would be: (3×412) + 360 + 463 = 2059
Ethanol has five C-H bonds, one C-O bond, one C-C bond and one O-H bond therefore the calculation would be: (5×412) + 360 + 348 + 463 = 3231
Propan-1-ol has seven C-H bonds, 2 C-C bond, one C-O bond and one O-H bond therefore the calculation would be: (7×412) + 360 + (2× 348) + 463 = 4403
Butan-1-ol has nine C-H bonds, 3 C-C bond, one C-O bond and one O-H bond therefore the calculation would be: (9×412) + 360 + (3×348) + 463 = 5575
Pentan-1-ol has eleven C-H bonds, 4 C-C bonds, 1 C-O bond and one O-H bond therefore the calculation would be: (11×412) + (4×348)+ 360 + 463 = 6747
Hexan-1-ol has 13 C-H bonds, 5 C-C bonds, one C-O bond and one O-H bond therefore the calculation would be: (13×412) + 360 + (5×348) + 463 = 7919
Heptan-1-ol has 15 C-H bonds, 6 C-C bonds, one C-O bond and one O-H bond therefore the calculation would be: (15×412) + 360 +(6×348) + 463 = 9091
Octan-1-ol has 17 C-H bonds, 7 C-C bonds, one C-O bond and one O-H bond therefore the calculation would be: (17×412) + 360 + (7×348) + 463 = 10263

From the above, I would find out who much energy how much energy is released. To find it I would use this formula: total energy involved to break bond – total energy involved to form bonds.

Methanol + Oxygen ⇒ Carbon dioxide + Water
2CH3OH + 3O2=> 2CO2 + 4H2O
2(2059)+3(496)=>2(2×743)+4(2×463) =

5606-6676= -1070joules

Ethanol + Oxygen⇒ Carbon dioxide + Water
2C2H5OH + 6O2 => 4CO2 + 6H2O
2 (3231)+6(496)=>4(1486)+6(926)

9438-11500= -2062joules

Propan-1-ol + Oxygen ⇒ Carbon dioxide + Water
2C3H7OH + 9O2 ⇒ 6CO2 + 8H2O
2(4403)+9(496)⇒6(1486)+8(926)

13270-16324= -3054joules

Butan-1-ol + Oxygen ⇒ Carbon dioxide + Water
2C4H9OH + 12O2 ⇒ 8CO2 + 10H2O
2(5575) + 12(496) ⇒ 8(1486) + 10(926)
17102 + 21148 = - 4046joules
Pentan-1-ol + Oxygen ⇒ Carbon dioxide + Water
2C5H11OH + 15O2 ⇒ 10CO2 + 12H2O
2(6747) + 15(496) ⇒ 10(1486) + 12(926)
20934-25972= -5038joules
Hexan-1-ol + Oxygen ⇒ Carbon dioxide + Water
2C6H13OH + 18O2 ⇒ 12CO2 + 14H2O
2(7919) + 18(496) ⇒ 12(1486) + 14(926)
24766-30796= -6030juoles
Heptan-1-ol + Oxygen ⇒ Carbon dioxide + Water
2C7H15OH +21O2 ⇒ 14CO2 + 16H2O
2(9091) + 21(496) ⇒ 14(1486) + 16(926)
28598+ 35620=-7022joules
Octan-1-ol+ Oxygen ⇒ Carbon dioxide + Water
2C8H17OH + 24O2 ⇒ 16CO2 + 18H2O
2(10263) + 24(496) ⇒ 16(1486) + 18(926)

32430-40444= -8014joules

The reactions are negative because reactions are exothermic and in exothermic reactions, ΔH is always negative. I have decided on my prediction it would be “the higher the number of carbon atoms the higher the energy released” so this means there is a link between the number of carbon atoms in a fuel and the energy released. Consequently, since the alcohols of my choice ranges from methanol to octan-1-ol I also predict that “octan-1-ol would release energy the most among all the alcohols because it has the highest number of carbons and methanol would release energy the least because it ...