Analysis of the Standard Enthalpy of Combustion for Alcohols Essay

purportTo investigate the standard heat content diversity of combustion for 5 consecutive alcoholic beverages in the alcohol homologic series, methanol, ethanol, propan-1-ol, butan-1-ol and pentan-1-ol, by use a calorimetric method to calculate the heat gained by the 100cm3 water in the experiment, and thus the heat lost by the alcohol lamp at standard temperature and pressing (298 K and 101.3 kPa). circumstance KnowledgeAlcohols are organic compounds containing Oxygen, Hydrogen and Carbon. The alcohols are a homologous series containing the functional OH group. As we move down the homologous series of alcohols, the number of Carbon atoms increase. Each alcohol molecule differs by CH2 a single Carbon atom and two Hydrogen atoms.Combustion is the oxidation of carbon compounds by oxygen in air to form CO2 and H2O. Combustion produces heat as well as carbon dioxide and water. The heat content change of combustion is the enthalpy change that occurs when 1 mole of a enkindle is b urned completely in oxygen.When alcohol undergoes complete combustion it produces carbon dioxide and water as products, and vim is released. The standard enthalpy of combustion of an alcohol (Hcomb) is the enthalpy change when one mole of an alcohol completely reacts with oxygen under standard thermodynamic conditions (temperature of 25C and pressure of 101.3 kPa). The standard enthalpy change of combustion of alcohols varies depending on their molecular size. The greater the number of carbons, the higher the standard enthalpy of combustion, as there is the presence of more bonds. The larger the alcohol molecule, the more bonds entrusting be broken and formed, and then more heat will be produced. apply experiments, the standard enthalpy of combustion of an alcohol hatful be found, buy first finding the heat released during the reaction employ the equationHeat= chaw of water item heat capacity of water rise in temperature of waterNote The specific heat capacity of water is 4.1 8 Jg-1C-1.and then finding the number of moles of alcohol burnt, and dividing the heat by this number.Equipment1. 250 cm3 conical flask2. 100 cm3 0.08 cm3 pipette3. Loggerpro thermometer4. 5 x different consecutive alcohol spirit burners (eg. methanol, ethanol, propanol, butyl alcohol and pentanol)5. Stand6. 2 x hugs7. Scales8. 1500 cm3 distilled water9. Heat proof mat10. MatchesMethod1. Connect the temperature detector to the datalogger. Connect the datalogger to the computer. Ensure the datalogging software is loaded and set to record the temperature of the sensor. Set the sampling rate to 1 sample per second for 210 seconds.2. Using the pipette, pipette 100 cm3 distilled water into the conical flask.3. Set up the stand, and clamp the conical flask 25 cm from the table. Also clamp the temperature probe 30 cm from the table, so that it is submerged in the distilled water but not in contact with the conical flask w eithers.4. bid the alcohol lamp (including its cap) using the scales and record the people.5. Place alcohol lamp directly under the conical flask on a heat proof mat.6. Click collect on datalogger to start recording the temperature. After 30 seconds, light the alcohol lamp.7. When the datalogger reaches 210 seconds immediately extinguish the flame by replacing the cap. Store the latest incline in loggerpro.8. Re-weigh the alcohol lamp (including cap) as soon as possible after extinguishing the lamp.9. Repeat go 2 8 with the analogous alcohol to obtain trail 2, and trial 3 results.10. Repeat move 2 9 for 4 other consecutive alcohols.11. Calculate the average change in mass of each alcohol and calculate the change in temperature of water for each trial.12. Calculate energy thoughtless by this using q=mcT then calculate Hcomb=qn13. Plot the chart of Hcombversus number of carbons in alcohol.Apparatustemperature probedatalogger device5 cm25 cmalcohol lamploggerpro collector on computerheatproof mat100 cm3 distilled waterconical flaskclampc lampVariables1. IndependentThe alcohol used to heat water will be changed, however each(prenominal) alcohols will be primary.The range of alcohols will be 5 consecutive alcohols from the homologous series methanol, ethanol, propan-1-ol, butan-1-ol, pentan-1-ol.1. interdependentThe change in temperature of the 100cm3 distilled water when heated by an alcohol lamp.1. Measure the initial temperature and final temperature using loggerpro. The change in temperature can be calculated by T=T(final)-T(initial)1. ControlledFinding the H using Hcomb=qnControlled VariablesHow is it controlled?Effect on experiment if uncontrolledType of liquidUsing completely distilled water for all trials throughout the experiment.Different liquids could result in a difference in the susceptibility of attractive forces between particles, meaning a different specific heat capacity which would affect the weighing of energy gain to water using the equation q=mcT, and thus an inaccurate enthalpy change value .Volume of liquid usedMeasure 100cm3 of distilled water by using 100 cm3 0.08 cm3 graduated pipette for each trial.If the volume was not exactly 100 cm3 it would directly affect the mass of the water which will affect the q=mcT value and thus the H value.Material glasswareUse the same brand and materials of a conical flask for all trials.Different materials have different conductivity and may absorb more heat from the alcohol lamp, affecting the overall heat absorbed by the distilled water. Using the same material and brand of conical flask ensures that this is the same for each experiment.Temperature of surroundingsFor standard enthalpy of combustion, the temperature must be 25C however in a classroom this is hard to control, so for each experiment the temperature will stay constant at 19C.If the surrounding temperature was to be changing, the distilled water could be losing more, or gaining more heat energy from the surroundings, directly affecting the temperature change and the refore, q=mcT and the H value.Distance between the conical flask and alcohol lampA clamp will be set at a distance of 25 cm from the table, and this the flask will sit at the same height each trial.If the distance changes, the heat lost to the surroundings varies and the heat that reaches the bottom of the calorimeter in like manner varies. This will lead to a difference in rise in temperature of water (T), and therefore an incorrect calculation for q=mcT and H value.Pressure of surroundingsFor standard enthalpy of combustion the pressure must be 1 atm, however in a classroom this is hard to obtain, so all experiments will be done in a room with the same pressure.Might influence the vaporisation pressure point, which will affect the q=mcT value, and thus the H.Duration of heatingThe water will be headed for 180 seconds.This ensures that all experiments have the same time to heat the water which directly do the change in temperature and thus the q=mcT calculation and the H value.R eferenceshttp//gandhijkt.org/blog/wp-content/uploads/2011/03/chemistry-sample-lab-report.pdfhttp//www.ausetute.com.au/heatcomb.htmlhttp//www.s-cool.co.uk/a-level/chemistry/chemical-energetics/revise-it/enthalpy-changes