PRACTICAL SCIENCE 3 TOPIC Purposes : FUEL : 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,c
H is negative. By definition, the heat of combustion is minus thec
enthalpy change for the combustion reaction, ie, -
H. 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/m. 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)
: 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 Whereas, m = molar v = volume q = msT Whereas, q = heat m = mass T = changes in temperature = mv 1000
Results : Kerosene: Initial temperature of water (oC) 28.0OC
Highesat temperature of water (oC) Increase in temperature (oC) Mass of lamp before burning (g) Mass of lamp after burning (g) Mass of kerosene burnt (g) Table 1 : The result of kerosene LPG: Initial temperature of water (oC) Highest temperature of water (oC) Increase in temperature (oC) Mass of lamp before burning (g) Mass of lamp after burning (g) Mass of LPG burnt (g) Table 2 : The result of LPG Wax: Initial temperature of water (oC) Highest temperature of water (oC) Increase in temperature (oC) Mass of lamp before burning (g) Mass of lamp after burning (g) Mass of wax burnt (g) Table 3 : The result of Wax
58.0OC 30.0OC 163.52 g 161.25 g 2.27 g
32.5OC 63.0OC 31.5OC 443.58 g 441.48 g 2.10 g
31.5OC 61.5OC 30.0OC 16.85 g 15.16 g 1.74 g
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
Fuel value for Kerosene C12H26 (l) + 37/2O2 q = m s T m = 200 g s = 4.18 Jg-1 0C T = 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) 12CO2 (g) + 13H2O (g)
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 H = -1929 KJ mol-1 Fuel value for LPG (Propane and Butane) 1. Propane C3H8 (l) + 5O2 (g) q = m s T m = 200 g s = 4.18 Jg-1 0C T = 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) 3CO2 (g) + 4H2O (l)
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 H = -522.5 KJ mol-1 2. Butane 2C4H10 + 13O2 q = m s T m = 200 g s = 4.18 Jg-1 0C T = 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 H = 696.6 KJ mol-1 8CO2 + 10H2
Fuel value of Wax C25H52 (s) + 38O2 (g) q = m s T 25CO2 (g) + 26H2O (g)
m = 200 g s = 4.18 Jg-1 0C T = 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 H = -5016 KJ mol-1 Overall fuel values: Types of fuel Kerosene LPG Wax Fuel value (KJmol-1) -1929 propane = -522.5 butane = -696.6 -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°C; and 275°C; (302°F; 527°F;). 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
1. 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. 2. If a LPG c