REQUEST FOR PRACTICUM INDUSTRY ADVISER

CHM170L Physical Chemistry 1 Laboratory 4th Quarter SY 2009-2010

Heat of CombustionNieva, Aileen D.1, Arceo, Mary Anne V., Cuales, Jelline C., Kim, Sung Min, Ngan, Emil Joseph T., Rivera, Jainie Lynne B.21Professor, School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology; 2Student (s), CHM170L/A41, School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology

ABSTRACTIn this experiment, the objectives are to be familiar with the calibration of bomb calorimeter, to determine and compare the heat of combustion of a non-aromatic and an aromatic compound and to use calorimetry in studying compounds of differing aromaticity. Heat of combustion, or enthalpy of combustion, is one of the standard enthalpies of transition or the standard enthalpy changes that accompany a change of physical state. It is the energy liberated as heat when one mole of a substance is burned in oxygen. A bomb calorimeter is commonly used to determine this physical quantity. 1351 Parr Bomb Calorimeter, designed to provide rapid and reliable heat of combustion values for solid and liquid fuels will be used to determine the heat of combustion of benzoic acid and naphthalene, which are aromatic compounds, and sucrose, a type of sugar.

Samples were obtained in the solid form, weighed and subsequently, pelletized using the pellet press and about 0.01 to 0.02g of iron wire was used as ignition. The bomb calorimeter was then set up and naphthalene followed by sucrose and benzoic acid were tested to calibrate the equipment. After combustion, the bomb was cleaned for combustion products.

We have observed that the aromatic compounds, naphthalene and benzoic acid, have higher heat of combustion compared to non-aromatic compounds such as sucrose. All in all, the objectives of this experiment are achieved. Students were acquainted with the use of the Parr 1351 calorimeter and explained how the structure of a compound can affect its heat of combustion.

INTRODUCTIONThe heat of combustion is the energy released as heat when a compound undergoes complete combustion with oxygen under standard conditions. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat.

A combustion reaction is a reaction in which a substance reacts with oxygen, usually with the release of heat and light to produce a flame.Calorimetry is the branch of physical chemistry dealing with the measurement of heat effects accompanying chemical or physical transformations. If this process occurs at a constant pressure, the heat measured directly is qp; it is qv when measured at constant volume. Heat changes in physical and chemical processes are measured with a calorimeter, a closed container designed specifically for this purpose.

Heat of combustion is usually measured by placing a known mass of a compound in a steel container called a constant-volume calorimeter, which is filled with oxygen at about 30 atm of pressure.Bomb Calorimeter connotes the explosive nature of the reaction in the presence of excess oxygen gas. The heat given off by the sample is absorbed by the water and the bomb. The special design of the calorimeter enables us to assume that no heat (or mass) is lost to the surroundings during the time it takes to make measurements. By measuring the temperature change of the water, the heat evolved from the sample burned (qv) can be determined. It is the change in internal energy (U) from its final state.The Parr 1351 Oxygen Combustion Bomb Calorimeter has been designed to provide rapid and reliable heat of combustion values for solid and liquid fuels.There are three main parts of the oxygen bomb calorimeter:

1. A bomb, which houses the sample and the oxygen for the combustion reaction.

2. The steel bucket, which holds a measured amount of water, the thermometer and the bomb.

3. The outer jacket, which thermally insulates the entire apparatusAdiabatic calorimetry is used primarily for the study of thermal hazards and the consequences of a maloperation during a process, for instance a misfeed or loss of cooling. This is because on larger scales the effective natural cooling rates are negligible in comparison to heat generation, and many large process vessels can therefore be considered to be adiabatic.

An adiabatic calorimeter is designed to simulate the thermal behaviour of larger scale chemical reactors, especially when studying uncontrolled and run-away reactions. METHODOLOGYEXPERIMENTAL METHOD

Equipment and Glassware

Bomb Calorimeter, pelletizer, power supply and oxygen tank

Parts of bomb calorimeter

The Reagents used are the following:

Benzoic acid, naphthalene, sucrose

Benzoic Acid C7H6O2 (or C6H5COOH), is a colorless crystalline solid and the simplest aromatic carboxylic acid. The name derived from gum benzoin, which was for a long time the only source for benzoic acid. This weak acid and its salts are used as a food preservative.

Naphthalene also known as naphthalin, naphthaline, moth ball, tar camphor, white tar, or albocarbo, is a crystalline, aromatic, white, solid hydrocarbon, best known as the primary ingredient of mothballs. It is manufactured from coal tar, and converted to phthalic anhydride for the manufacture of plastics, dyes and solvents.

Sucrose also called saccharose, is a disaccharide with the molecular formula C12H22O11. Its systematic name is -D-glucopyranosyl-(12)--D-fructofuranose. It is best known for its role in human nutrition and is formed by plants but not by higher organisms.

Experimental Procedure

You will perform the combustion of benzoic acid twice to calibrate the bomb.

You will determine the heat of combustion of naphthalene. Do an absolute minimum of two runs.

You will use calorimetry to study compounds with differing aromaticity.

Prepare a pellet of sample (sucrose, benzoic acid or naphthalene). Use less than one gram of solid to do this. Then weigh the pellet accurately and place in the dish inside the bomb. Weigh a ten cm. piece of ignition wire and then connect this to terminals inside the bomb.

Assemble the bomb adding exactly 2000 ml of distilled H2O using the large graduated cylinder provided for this purpose.

Using the bomb calorimeter is used to determine the enthalpy of combustion which is consists primarily of 25 atm of oxygen gas and the stainless steel bomb reaction vessel containing a weighed sample of the compound surrounded by a liquid, such as water, that absorbs the heat of the reaction and thus increases in temperature to insure complete combustion. The combustion reaction is initiated by passing an electrical current through an iron fuse wire in contact with the sample. The reaction vessel is immersed in an insulated water bath. The heat released in the combustion reaction is absorbed by the water and the other parts of the calorimeter, thereby causing the temperature of the calorimeter to rise.

Upon completion of the run, remove the bomb and place it in the steel receptacle. CAREFULLY release the pressure by loosening the needle valve on top of the bomb. Weigh the remnants of the ignition wire.

Clean up the bomb and prepare it for the next run. The 2000 ml of distilled H2O is to be reused for all succeeding runs. Since some loss of H2O occurs during a run, it is necessary to re-measure .Record the room temperature as this will be necessary to calculate the stem correction.Samples

Benzoic AcidNaphthaleneSucrose

Sample mass,g1.047 g0.518 g1.059 g

Mass of fuse wire before combustion, g0.016 g0.015 g0.017 g

Mass of fuse wire after combustion, g0.002 g0.003 g0.003 g

Mass of wire that combusted0.014 g 0.012 g0.014 g

Change in Temperature2.071716 C2.06438 C1.75468 C

Measured H of combustion, cal/g6143.07 cal/ g9070.67 cal/ g3763.51 cal/ g

Corrected H of combustion, cal/g7543.084 cal/g10470.602 cal/ g5163.52 cal/ g

Literature value of H of combustion, cal/g6318 cal/ g9617 cal/ g3944 cal/ g

Percentage Error19.3%8.8%28%

RESULTS AND DISCUSSIONThrough the experiment it shows that with the combustion of benzoic acid with mass of 1.047 g, it shows that the measured H of combustion is 6143.0 cal/g. with this value the percentage of error was 19.3 percent. The next sample was the naphthalene and through the combustion of 0.518grams of this sample the H for was 9070.6 which is relatively has a small difference as to compare it to its corrected value and for it the percentage error was only 8.8 percent. The last sample was the sucrose. The sample gathered weighed 1.059 g and through combustion, the delta H measured was 3763.51 cal /g and for it the corrected value is 5163.52 in which the percent error became a little bit high. The reason behind is perhaps because of the wire place inside the bomb. For instance the wire placed for the sucrose and benzoic acid left a 0.014g because in getting the corrected values we also need to take into consideration the mass of the wire. The main purpose of the wire is to know whether the placed sample is combustible or not. In getting the amount of mass combusted, one must weigh first the mass of the wire before the combustion then minus it to the mass of the wire after combustion. All of the data such as the delta H of combustion were gathered from bomb calorimeter machine.

Comparing the three compounds, as observed, the mass wire combusted for the benzoic acid and sucrose was a little bit bigger than the mass of the naphthalene it only means that naphthalene is more combustible, this is because naphthalene is less stable than the other two. It has been stated that a compound that is less stable will become more energy released. Naphthalene is a less stable compound it is because the structure was composed of two aromatic benzene ring which has been fused together. While sucrose is a cycloalkane which can be easily be broke the OH bonds.

Benzoic Acid

Naphthalene

SucroseREFERENCES1. General Chemistry The Essential Concepts by Raymond Chang2. Experiment in Physical Chemistry by Shoemaker, D.P.

3. Oelke, W.C. and Zuehlke, R.W. (1969) Laboratory Physical Chemistry, Van Nostrand Reinhold Company, New York, NY.

4. Physical Chemistry Laboratory Manual, Part 1 (2006) by Alvin R. Caparanga, John Ysrael G. Baluyut and Allan N. Soriano

5. Physical Chemistry by Silbey and Alberty

6. Physical Chemistry by David W. BallAPPENDICES

SAMPLE COMPUTATIONSCorrected H of combustion

= measured H of combustion + 1400 x mass of wire that combusted

For benzoic acid:

= 6143.07 cal / g + 1400 + 0.014 g

= 7543.084 cal /g

% error = AV-EV x 100

AV

= 19.3%

Oxygen tank

bomb calorimeter

Power supply

pelletizer

Experiment 06 Group No. 4 01 June 2010

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