• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
Page
  1. 1
    1
  2. 2
    2
  3. 3
    3
  4. 4
    4
  5. 5
    5
  6. 6
    6
  7. 7
    7
  8. 8
    8
  9. 9
    9
  10. 10
    10

To investigate the enthalpy change of combustion for various alcohols.

Extracts from this document...

Introduction

Chemistry Coursework P l a n n i n g Aim: To investigate the enthalpy change of combustion for various alcohols Alcohols will be burnt to heat up water. The aim is to find out how much energy is produced when burning the following alcohols : ethanol, propanol and butanol. Alcohols react with oxygen in the air to form carbon dioxide, water and energy is liberated (exothermic reaction), because the reactants' energy is higher than that of the products'. The alcohols form a series of compounds which are related to each other. This is called a homologous series and has the formula : Cn H 2n+1 OH In this investigation the alcohols used were: ethanol, propanol and butanol. Ethanol : C2H5OH Propanol : C3H7OH Butanol : C4H9OH Combustion Reactions: Ethanol : C2H5OH + 3O2 2CO2 + 3H2O + heat Propanol : C3H7OH + 4.5O2 3CO2 + 4H2O + heat Butanol: C4H9OH + 6O2 4CO2 + 5H2O + heat Heat (joules) = T x mass (g) x specific heat capacity Heat energy = rise in temperature x mass of water (g) x 4.18 The specific heat capacity is the number of joules required to raise the temperature of 1g of water by 1oC (1g of H2O raised by 1oC = 4.18 joules) The combustion of the alcohols is not exactly as shown in the equation because some carbon is deposited on the calorimeter base ie. C2H5OH + O2 2C + 3H2O Additionally, some carbon monoxide is produced ie. C2H5OH + 2O2 2CO + 3H2O Therefore the equation provided for the complete combustion is an over simplification. Prediction: When bonds are broken, energy is absorbed by the system (endothermic process); and when bonds are formed, energy is released to the external environment (exothermic process). When alcohols are burnt, the reaction is always overall exothermic. Therefore more energy is being released than is being consumed. Thus, a qualitative prediction is that each alcohol will burn exothermally and therefore the temperature of the water will rise. ...read more.

Middle

* The calorimeter was weighed again, making sure it is still the same weight. If the weight was more/ less, the new weight was recorded, taking it into account when working out the mass of water. * Experiment was then repeated 5 times for each alcohol. R e s u l t s Using the relationship: heat = temperature rise x mass water x 4.18 No. of moles = mass/ RFM ETHANOL: Experiment Temperature rise (oC) Mass of water(g) Heat (J) Number of moles ?Hc (kJmol-1) 1 30.0 54.2 6796.6800 0.01300 522.8 2 26.5 54.2 6003.7340 0.00978 613.9 3 26.3 54.2 5958.4228 0.01150 518.1 4 26.0 54.2 5890.4560 0.01130 521.3 5 27.0 54.2 6117.0120 0.01196 511.5 Method of calculating results obtained: 1.) 30.0 x 54.2 x 4.18 = 6796.68 joules energy produced by 0.6g ethanol no. of moles of ethanol = mass/RFM = 0.6 / 46 = 0.013 As 0.013 moles of ethanol liberate 6796.68 joules energy Therefore 1 mole of ethanol liberates 6796.68 / 0.013 = 522821.5 joules or 522.8 kJmol-1 2.) 26.5 x 54.2 x 4.18 = 6003.734 joules energy produced by 0.45g ethanol no. of moles of ethanol = mass/RFM =0.45 / 46 = 0.00978 As 0.00978 moles of ethanol liberate 6003.734 joules energy Therefore 1 mole of ethanol liberates 6003.734 / 0.00978 = 613878.7 joules or 613.9 kJmol-1 simply from comparing this result to the other results, I can see that it is anomalous. However, I would need to draw a graph to compare how abnormal the result is. However, comparing the result with the literary values, this result may be the closest to the true values (least amount of heat lost to the atmosphere). 3.) 26.3 x 54.2 x 4.18 = 5958.4228 joules energy produced by 0.53g ethanol no. of moles of ethanol = mass/RFM = 0.53 / 46 = 0.0115 As 0.0115 moles of ethanol liberate 5958.4228 joules energy Therefore 1 mole of ethanol liberates 5958.4228 / 0.0115 = 518123.7 joules or 518.1 kJmol-1 4.) ...read more.

Conclusion

Sufficiency of evidence: The experiment was repeated five times for each alcohol. This gave only five results to plot on a graph. If there had been more anomalous results, I would not have had enough data to compare them with so as to determine the anomalous results. Improvement: Obvious improvements would be to make the combustion more efficient so that no carbon was deposited and no carbon monoxide was produced. This could be achieved by designing a burner rather than using a wick. As with a gas oven, the fuel needs to be in gaseous form for the most efficient combustion. One reason why the results obtained were inaccurate is that some of the heat liberated was used to vaporise the liquid prior to its combustion. A suitably designed burner could get around this - presumably using several fine holes rather than one big hole to get better mixing of the vapour with the oxygen. Another modification might be to use oxygen enriched air or even pure oxygen to ensure the complete combustion of the alcohol. Perhaps a cylindrical reflective metal sheet could be placed around the burner and calorimeter to prevent the heat being lost to the surroundings e.g. a sheet of aluminium. Further work to provide additional evidence or extend enquiry: To further my enquiry I would investigate in the same way the combustion of methanol (CH3OH) and pentanol (C5H11OH). This would give me further evidence to conclude that: the larger the alcohol molecule, the more bonds will be broken and formed, and therefore the more heat will be produced. For this enquiry, I would predict that methanol would produce less heat than all of the alcohols, and that pentanol would produce the most heat. In conclusion, the experiment was worthwhile as it showed the relationship between different sized alcohol molecules in a combustion reaction. However, the evidence is not accurate enough to show any other information, other than the fact that the larger the alcohol molecule the more heat is produced during combustion. Tania Lapa ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Organic Chemistry section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Organic Chemistry essays

  1. Marked by a teacher

    Experiment to investigate the heat of combustion of alcohols.

    4 star(s)

    Therefore I predict that: * The longer the molecule of alcohol, the larger the amount kJ/mol is given out by burning the substance. To back this prediction, I have calculated some theoretical values to show how the amount of energy released increases as the number of carbon atoms rises.

  2. Comparing the heat energy produced by combustion of various alcohols

    It is because I want to make this experiment be a fair test. So that, every time, I raise 30 ? then gets the alcohols out. Prediction In this experiment, I will predict that as the weight of the alcohols is given more, then the temperature of the water goes

  1. Investigating the Combustion of Alcohols

    The safety precautions involved in this experiment include wearing goggles to avoid any injury to the eye and a lab coat to protect clothing and skin. Since alcohols are toxic and flammable when spilt or handled incorrectly, can be a severe hazard.

  2. Titration experiment - write up

    The volumetric flask has a percentage error of 0.24%. During my experiment I made sure to shake the volumetric flask, so that, I could ensure that the standard solution was mixed thoroughly. In addition if the equipment was not properly cleaned then my solution would have been contaminated resulting in inaccurate results.

  1. To measure and compare the enthalpy change of combustion for four different types of ...

    When moving equipment make sure that it is moved slowly and carefully as broken equipment can cause damage. More importantly is not to move the top pan balance as it could change the readings. Simple things like no sitting down and hair being tied back has to be taken into account as well.

  2. Comparing the enthalpy changes of combustion of different alcohols.

    * Safety goggles and lab coat * Box of matches * Pen and paper to record the results * Paper towels to help clean soot off the bottom of the can Variables. * Draught * Amount of water * Material of can * Starting temperature of water * Temperature rise

  1. The Combustion of Alcohols and the factors affecting these reactions

    Therefore the number of carbon atoms should be proportional to the energy released per mole. Alcohol Enthalpy (kJ/mol) Methanol 1007 Ethanol 1281 Propanol 1901 Butanol 2521 Pentanol 3141 The larger the molecule the more energy needed to break more bonds, but more energy is released when more new bonds are formed.

  2. GCSE Chemistry Revision Notes - everything!

    follows: Potassium, Sodium, Lithium, Calcium, Magnesium, Aluminium, (Carbon), Zinc, Iron, Tin, Lead, (Hydrogen), Copper, Silver, Gold and Platinum. This order is with decreasing reactivity. Any metal higher in the series will displace one lower down from its compound. For example, if you heated magnesium and copper (II)

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work