PRACTICAL SCIENCE 3

TOPIC : FUEL

Purposes : To determine the fuel values for kerosene, LPG and wax.

Theoretical background:

Heat of Combustion of a substance is the heat liberated when 1 mole of the substance

undergoes complete combustion with oxygen at constant pressure. Combustion is

always exothermic, cH is negative. By definition, the heat of combustion is minus the

enthalpy change for the combustion reaction, ie, - cH. By definition, the heat of

combustion is a positive value. Heat of Combustion can be measured experimentally.

The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon

dioxide, water and heat. The heating value or calorific value of a substance, usually a

fuel or food, is the amount of heat released during the combustion of a specified amount

of it. The calorific value is a characteristic for each substance. It is measured in units of

energy per unit of the substance, usually mass, such as: kcal/kg, kJ/kg, J/mol, Btu/m³.

Heating value is commonly determined by use of a bomb calorimeter.

Apparatus :

Copper can

Tripod stand

100cm3 measuring cylinder

Thermometer

Spririt lamp

Electronic balance

Pipe-clay triangle

Windshield

Wooden block

Chemical materials : Kerosene

LPG (Laboratory gas)

Wax (candle)

Diagram :

Procedures : 1. Using a measuring cylinder, 200 cm3 of water was poured into a

copper can.

2. The copper can was placed on a tripod stand.

3. The initial temperature of the water was measured and recorded.

4. A windshield was placed as in the diagram.

5. 50 cm3 of kerosene was poured into a spirit lamp and the mass of

the lamp and its content was recorded.

6. The lamp was put under the copper can as shown in the diagram

and the wick of the lamp was lighted up immediately.

7. The water was stirred throughout the experiment.

8. The flame was put off when the temperature of the water increases

by 30oC. The highest temperature reached by the water was

recorded.

9. The mass of the lamp and its content was weighed and recorded

immediately.

10.Steps 1 to 9 was repeated using wax (candle).

11.Steps 1 to 9 were repeated using LPG.

Formula for calculation:

No of mol = mv

1000

Whereas,

m = molar

v = volume

q = ms∆T

Whereas,

q = heat

m = mass

∆T = changes in temperature

Results :

Kerosene:

Initial temperature of water (oC) 28.0OC

Highesat temperature of water (oC) 58.0OC

Increase in temperature (oC) 30.0OC

Mass of lamp before burning (g) 163.52 g

Mass of lamp after burning (g) 161.25 g

Mass of kerosene burnt (g) 2.27 g

Table 1 : The result of kerosene

LPG:

Initial temperature of water (oC) 32.5OC

Highest temperature of water (oC) 63.0OC

Increase in temperature (oC) 31.5OC

Mass of lamp before burning (g) 443.58 g

Mass of lamp after burning (g) 441.48 g

Mass of LPG burnt (g) 2.10 g

Table 2 : The result of LPG

Wax:

Initial temperature of water (oC) 31.5OC

Highest temperature of water (oC) 61.5OC

Increase in temperature (oC) 30.0OC

Mass of lamp before burning (g) 16.85 g

Mass of lamp after burning (g) 15.16 g

Mass of wax burnt (g) 1.74 g

Table 3 : The result of Wax

Observation:

Figure 2 : Initial and final temperature of water was taken

Figure 3 : Use candle to determine its fuel values

Figure 4 : The aluminum can was closed by lit to avoid heat releases to surrounding

Calculation:Fuel value for Kerosene

C12H26 (l) + 37/2O2 12CO2 (g) + 13H2O (g)

q = m s ΔT

m = 200 g

s = 4.18 Jg-1 0C

ΔT = 30.0 0C

q = (200) g x (4.18) Jg-1 0C-1 x (30 .0) 0C

= 25080 J

=25.08 KJ

Molar mass of kerosene, C12H26 (C=12, H=1)

No. of mol of kerosene, C12H26 = mass/molecular Relative Mass, Mr

= 2.27 / 12(12 + 26(1)

= 0.013 mol

1 mol of kerosene = 25.08

0.013

ΔH = -1929 KJ mol-1

Fuel value for LPG (Propane and Butane)

1. Propane

C3H8 (l) + 5O2 (g) 3CO2 (g) + 4H2O (l)

q = m s ΔT

m = 200 g

s = 4.18 Jg-1 0C

ΔT = 30.0 0C

q = (200) g x (4.18) Jg-1 0C-1 x (30 .0) 0C

= 25080 J

=25.08 KJ

Molar mass of Propene, C3H8 (C=12, H=1)

No. of mol of Propane, C3H8 = mass/molecular Relative Mass, Mr

= 2.10 / 3(12 + 8(1)

= 0.048 mol

1 mol of Propane = 25.08

0.048 mol

ΔH = -522.5 KJ mol-1

2. Butane

2C4H10 + 13O2 8CO2 + 10H2

q = m s ΔT

m = 200 g

s = 4.18 Jg-1 0C

ΔT = 30.0 0C

q = (200) g x (4.18) Jg-1 0C-1 x (30 .0) 0C

= 25080 J

=25.08 KJ

Molar mass of Butane, C4H10 (C=12, H=1)

No. of mol of Butane, C4H10 = mass/molecular Relative Mass, Mr

= 2.10 / 4(12 + 10(1)

= 0.036 mol

1 mol of Butane = 25.08

0.036

ΔH = 696.6 KJ mol-1

Fuel value of Wax

C25H52 (s) + 38O2 (g) 25CO2 (g) + 26H2O (g)

q = m s ΔT

m = 200 g

s = 4.18 Jg-1 0C

ΔT = 30.0 0C

q = (200) g x (4.18) Jg-1 0C-1 x (30 .0) 0C

= 25080 J

= 25.08 KJ

Molar mass of wax, C25H52 (C=12, H=1)

No. of mol of kerosene, C25H52 = mass/molecular Relative Mass, Mr

= 1.74 / 25(12 + 52(1)

= 0.005 mol

1 mol of kerosene = 25.08

0.005

ΔH = -5016 KJ mol-1

Overall fuel values:

Types of fuel Fuel value (KJmol-1)

Kerosene -1929

LPG propane = -522.5

butane = -696.6

Wax -5016

Discussion:

In this experiment, I have used 3 substances which is kerosene, LPG and wax in

which we needed to find its fuel values. First, we used kerosene or kerosine, colorless,

thin mineral oil whose density is between 0.75 and 0.85 grams per cubic centimeter. A

mixture of hydrocarbons, it is commonly obtained in the fractional distillation of

petroleum as the portion boiling off between 150&degC; and 275&degC; (302&degF;–

527&degF;). Kerosene has been recovered from other substances, notably coal (hence

another name, coal oil), oil shale, and wood. At one time kerosene was the most

important refinery product because of its use in lamps. Now it is most noted for its use

as a carrier in insecticide sprays and as a fuel in jet engines. The fuel value of kerosene

that I obtained in this experiment is -1929 KJ mol-1.

Second, we used liquefied petroleum gases(LPG). The LPG comprise propane

and butane or a mixture of these two hydrocarbons. They can be liquefied under low

pressure (5-10 atmospheres). In the liquid state and at a temperature of 38 degrees C

they have a relative vapour pressure less than or equal to 24.5 bars. Their specific

gravity ranges from 0.50 to 0.58. These are the light hydrocarbons fraction of the

paraffin series, derived from refinery processes, crude oil stabilisation plants and natural

gas processing plants comprising propane and butane or a combination of the two.

They are normally liquefied under pressure for transportation and storage. The fuel

value of propane that was used in this experiment is -522.5 KJ mol-1 while for butane is -

696.6 KJ mol-1.

And lastly, we used wax. Chemically, a wax is a type of lipid that may contain a

wide variety of long-chain alkanes, esters, polyesters and hydroxy esters of long-chain

primary alcohols and fatty acids. They are usually distinguished from fats by the lack of

triglyceride esters of glycerin (propan-1,2,3-triol) and three fatty acids. In addition to the

esters that contribute to the high melting point and hardness of carnauba wax, the

epicuticular waxes of plants are mixtures of substituted long-chain aliphatic

hydrocarbons, containing alkanes, fatty acids, primary and secondary alcohols, diols,

ketones, aldehydes. Paraffin waxes are hydrocarbons, mixtures of alkanes usually in a

homologous series of chain lengths. Waxes are used to make wax paper, impregnating

and coating paper and card to waterproof it or make it resistant to staining, or to modify

its surface properties. Waxes are also used in shoe polishes, wood polishes, and

automotive polishes, as mold release agents in mold making, as a coating for many

cheeses, and to waterproof leather and fabric. Wax has been used since antiquity as a

temporary, removable model in lost-wax casting of gold, silver and other materials. The

fuel value of wax that we obtained from this experiment is -5016 KJ mol-1.

The theoretical fuel values of these three substance, kerosene, butane and

propane is -7513 KJ mol-1, -527 KJ mol-1 and -683 KJ mol-1 respectively. The values

that we obtained are slightly lower due to its major possibilities, which is the occurrence

of incomplete combustion. Incomplete combustion mainly occurs due to lack of oxygen

surrounding the combustion area. This is unparallel with the theoretical values that are

based on full or completed combustion.

There are some precautionary steps that need to be taken while doing this

experiment, such as:

The fans have to be turned off to make sure the reading of the weight of the

substances is correct.

The kerosene and LPG have to be handle carefully because it is highly

flammable.

The eyes have to be place in parallel with the reading scale of the thermometer

to avoid any parallax error.

The thermometer have to be make sure is not touching the copper can while

combustion is occurring to prevent the thermometer from showing the incorrect

reading.

Beware of the sooth produced during the combustion due to its danger to health.

Questions:

1. State the 6 factors that affect the selection of a fuel to be used in industries.

a. Cost

b. Fuel values

c. Availability

d. Effect to environment

e. Storage space to store fuel

f. Technology used to harness the energy from the fuel

g. Have a moderate rate of combustion

2. If you are given wax, kerosene and LPG, which one would you choose to use for your camping trip for cooking your meals? Explain.

I will choose LPG in my camping trip for cooking my ameals. There are several

reasons why I chose this substance. First of all, is because it is very light and

user-friendly. I said it that way is because it is stored in a can, which is very

portable and it is also very easy to use. Besides that, LPG also did not produce

any kind of smoke and soot. Not to forget, LPG also is the substance that has the

highest fuel values compared to these 3 substances.

3. If a LPG contains only butane and propane, write equations for the combustion of these two hydrocarbons.

Combustion of Butane =

C4H10 + 132 O2 4CO2 + 5H2O

Combustion of Propane =

C3H8 + 5O2 3CO2 + 4H2O

4. Explain why the fuel values obtained are less than theoretical values.

It gives different values and less than the exact value because of some heat will

lost to the environment when the burning process. Besides that not all the heat

absorb by the water, it is also absorbed by the copper can. Other reason why the

values reach approximate values because during reading the thermometer, must

be error occurred which is parallax error where we read the reading, our eyes is

not parallel to the thermometer. We cannot determine where the highest

temperature is attained so the different in temperature will make the different in

temperature. We actually need to get even temperature so that we can get more

accurate result. Lastly, incomplete supply of oxygen throughout the combustion

also can make the heat values decrease its number.

Reflection:

While doing this experiment, there are several aspects that has to be taken

seriously. For example, the importance of making sure that the apparatus that you want

to use is in the correct condition. In this case, the copper case that we used is not fully

function for some of us and the apparatus and materials are not even enough for every

partner in the class. So, we have to share our apparatus and combines with other

groups and shares our result and calculation with them. Besides that, we have to make

sure that we take the correct reading of the weight of the candle, Bunsen burner and the

lamp to make sure that our readings and results did not run too far off the theoretical

fuel values.

Conclusion:

As a conclusion, every fuel substances has its own fuels values that differs from

one kind of another. The amount of fuel values ussualy deters by its amounts of carbon

in that particular substances. And we have found out in this experiment, wax has the

highest amount of fuel values and carbon per molecule in it meanwhile LPG has the

lowest and kerosene is in the middle.