• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Enthalpy of Combustion of Alcohols Lab

Extracts from this document...

Introduction

MOLAR ENTHALPY OF COMBUSTION OF ALCOHOLS Lab Asad Ali Tayyab IB HL Chemistry 2 Grade 12 Lab Work Block 8 Mr. Graham MOLAR ENTHALPY OF COMBUSTION OF ALCOHOLS AIM: The purpose of this investigation is to use calorimeter to determine the molar enthalpy change in the combustion of each of a series of alcohols (Methanol, Ethanol and Butan-1-ol) RESEARCH QUESTION: How do the molar enthalpies of combustion change as the alcohol molecules become larger from methanol to ethanol to butan-1-ol? HYPOTHESIS: I think that as the molecules become larger, the enthalpy of combustion will increase. This hypothesis is based on my assumption that as the molecule becomes larger, more bonds are added to a substance. The more the bonds, the harder it is to separate the molecule and the more energy is required to combust the substance. INTRODUCTION: The molar enthalpy of combustion (?H) of a substance is the change of enthalpy, when 1 mole of a substance in its standard state (298 K and 1 atm pressure) is burnt to form products in their standard states. ?Hc may be calculated from standard enthalpies for formation of each of the substances involved in the combustion reaction, or can be estimated from bond enthalpies. Enthalpies of formation are usually obtained directly from combustion experiments. ?Hc is measured in calories. ...read more.

Middle

+ (5 x 1) + (16) + (1) M = 46.0 gmol-1 m = 1.06 g n = 1.06g/46.0 gmol-1 n = 0.0230 mol Step 2: Calculating heat energy given out Q = mC?T m = 100g C = 4.186 Jg-1k-1 ?T = 11.0k Q = (100g) (4.186 Jg-1k-1) (11.0k) Q = 4604.6 J Q = 4.60 kJ Step 3: Calculating the enthalpy of combustion ?HC = Q/mol ?HC = 4.60kJ 0.0230mol = 200 kJ/mol However it is exothermic, that is why it has to be negative = - 200 kJ/mol Step 4: Calculating the uncertainties Uncertainty for mass of alcohol combusted = (0.02g/1.06g) x 100 1.78% Uncertainty for volume of water: (0.05cm3/100cm3) * 100 = 0.05 % Therefore uncertainty for mass of water: 0.05% Uncertainty for change in temperature = (0.02/11.0) x 100 = 0.18% Total Uncertainty = 2.01 % ENTHALPY OF COMBUSTION OF ETHANOL = - 200 kJ/mol � 2.01 % BUTAN-1-OL: Step 1: Calculating the number of moles of Butanol combusted n = m/M C4H9OH M = (4 x 12) + (9 x 1) + (16) + (1) M = 74.0 gmol-1 m = 0.29 g n = 0.29g/74.0 gmol-1 n = 0.00390 mol Step 2: Calculating heat energy given out Q = mC?T m = 100g C = 4.186 Jg-1k-1 ?T = 11.0k Q = (100g) ...read more.

Conclusion

This was an error as methanol and ethanol are volatile liquids and the fact that the alcohol lamps were hot after the combustion indicates that some of the alcohols would have escaped which increases the uncertainty in the labs. In addition, one other reason that could affect the results of our lab is that the beaker might have absorbed some heat. The beaker was made of Pyrex glass and certainly absorbed some heat. This means that before the temperature of the water started to change, the beaker might have absorbed some heat and this affects the results as some energy is wasted in this process. Similar to this was the stirring rod and the thermometer which absorbed some heat as well further making the experiment less accurate. Furthermore, random errors certainly played a part in affecting the results as we had uncertainties for mass, temperature and volume. Even though random errors were comparatively small to affect the result, nevertheless, all these uncertainties add up to be large enough to affect the results of the lab. For random errors, we can take certain measures to reduce the uncertainty and increase the accuracy of our lab. Also, we can measure the mass of water to try and reduce the uncertainty due to our assumption made of the density of water. For lowering the uncertainties even more, we can use a digital thermometer so that if the thermometer has a lower uncertainty, the percentage uncertainty will decrease. ?? ?? ?? ?? ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our International Baccalaureate 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 International Baccalaureate Chemistry essays

  1. Combustion of alcohols lab report

    4638 65.22 Octanol 11336.91 130 4210.85 5294 79.54 Nonanol 7341.63 144 5564.18 5947 93.56 Table to show energy differences between preceding alcohols Name of alcohol Number of Carbon atoms Energy liberated (J) Energy difference between preceding alcohol Ethanol 2 7952.37 Propanol 3 8587.89 635.52 Butanol 4 7984.47 603.42 Pentanol 5

  2. The Enthalpy of Neutralization

    + H2SO4(aq)--> Na2SO4(aq) + 2H2O(l) Finding the Moles of Water Moles of sulfuric acid: [Volume x Concentration] 0.025dm3 x 2.00mol�dm-3 = 0.050mol H2SO4 Moles of sodium hydroxide: [Volume x Concentration] 0.025dm3 x 4.00mol�dm-3 = 0.100mol NaOH (x2) = 0.200mol NaOH Moles of water: [Equal to moles of limiting reagent] 0.050mol H2SO4 --> 0.050mol H2O(x2)

  1. A comparison of various proprieary antacids

    Moles of sodium hydroxide=0.0118 moles �0.21% Initial moles of HCl= 0.0125 moles (� 0.24%) Moles of HCl that reacted with 1.25cm3 NaOH=0.0118 moles ( �0.21%) Moles of HCl that react with the antacid = 0.0125 moles (� 0.24%)-0.0118 moles ( �0.21%)

  2. Enthalpy of Combustion Lab Report

    The stopwatch used for each trial has also been kept constant throughout the experimental procedure. 4. The thermometer used for each trial has also been kept constant throughout the experimental procedure. Observations: 1. The ethanol was burnt with a yellow flame.

  1. Thermodynamics: Enthalpy of Neutralization and Calorimetry

    of Neutralization of NaOH kcal/mol ?H neutralization kcal/mol = ?H neutralization kcal/mol = ?H neutralization kcal/mol = -30.65 -30.65 �.072 kcal Enthalpy of Neutralization of NaOH and HCl kJ/mol -30.65 �.072 kcal -128.24 �. 072 kJ/mol Heat Capacity of Calorimeter -Table 1 Trial 1 Trial 2 Trial 3 Measured Average

  2. Determination of Heat of Combustion of Ethanol

    To improve this, I could have used a calorimeter so as to reduce the heat loss and so that I could calculate the amount of heat lost to the surroundings.

  1. Chemistry Lab Report- Determining the Enthalpy of Enthalpy Change, H, for a Redox Reaction ...

    Evaluating procedure(s): : There are weaknesses and limitations in this experiment. Systematic error, such as poor insulation of calorimeter has caused the results to be inaccurate in relation to the accepted value. From the graph, we see that there was a temperature decrease, which logically means that the insulation from

  2. Bomb calorimetry. The goal of this experiment was to use temperature data over ...

    no inflow or outflow of heat and its insulated jacket serves as an ideal environment for the bomb. All the conditions surrounding the bomb and its calorimeter, allow for an adiabatic reaction to take place. Hence, the ΔU is equal to the work (w = -pâV)

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