• 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

# Comparing The Enthalpy Change OfCombustion Of Different Alcohols

Extracts from this document...

Introduction

Comparing The Enthalpy Change Of Combustion Of Different Alcohols The aim of my experiment is to investigate the enthalpy of combustion of a range of alcohols. The standard enthalpy of combustion is the enthalpy change that occurs when 1 mole of a fuel is burned completely in oxygen under standard conditions - 1 atmosphere pressure and 298K. All combustion reactions are exothermic which is why I am expecting all the values for the enthalpy change of combustion to always be negative. Prediction I predict that the greater the number of carbon atoms there are in the alcohol molecule, the greater the enthalpy change of combustion it will have. This is because in a chemical reaction energy is needed in order to break bonds and energy is released when bonds are made. If I were to look at these two values; the energy required to break the bonds of the reactants and the energy released when the bonds of the product are made then I am able to work out the enthalpy change of combustion of the alcohol. In order to do this we need to know the bong enthalpies of the bonds in the process. The quantity of energy needed to break a particular bond in a molecule is called the bond enthalpy. Below is a table containing the bond enthalpies of the bonds that occur in the combustion of an alcohol. Bonds Average bond enthalpy/kJ mol-1 C-C +347 C-H +413 C-O +358 O-H +464 O=O +498 C=O +805 By looking at the equation for the reaction that occurs when an alcohol burns, we realise that the reaction involves both breaking bonds and making new ones. From the equation of the process we can tell how many of the different number of bonds are broken and made and so work out the enthalpy change of combustion. We can work out the enthalpy of combustion of methanol by using the bond enthalpy values: We can use the enthalpy cycle above to work out the value for the enthalpy change of combustion of methanol, represented by ?H1. ...read more.

Middle

d) I will use 5 different alcohols, which is a sensible range in order to gather sufficient data to find a relationship between the enthalpy change of combustion and the number of carbon atoms in the alcohol. e) wait for the temperature to stay 5 alcohol which will give me a good range and so my results being more reliable Results Alcohol Temperature of water at start Temperature of water at end Temperature Change of water Mass of water (g) Mass of copper container and aluminium can (g) Total mass (g) Start mass of burner (g) End mass of burner (g) Mass of fuel used methanol 19 84 65 96.98 68.20 165.18 142.48 137.94 4.54 23 80 57 102.44 68.20 170.64 142.90 139.08 3.82 Ethanol 24 84 60 88.29 68.20 156.49 159.08 156.32 2.76 18 87 69 102.16 68.20 170.36 153.53 150.20 3.33 propan-1ol 21 83 62 103.47 68.20 171.67 141.85 139.97 1.88 15 79 64 109.5 68.20 177.70 170.39 167.55 2.84 butan-1-ol 18 84 66 94.45 68.20 162.65 135.35 132.47 2.88 16 92 76 90.76 68.20 158.96 170.69 167.50 3.19 Pentanol 27 86 59 103.17 68.20 171.37 143.41 140.90 2.51 24 82 58 100.58 68.20 168.78 138.15 135.71 2.44 I have chosen to repeat the experiments for each alcohol twice. Also I have taken results over a large temperature range. This means than all the values in my results will be greater and as values increase so does their accuracy and therefore I am expecting more reliable results. To work out the enthalpy change of combustion for the alcohols, I need to first work out the energy transferred to both the copper container and the water. I do this by using two constants; the specific heating capacity of water and copper. I also use the temperature rise of the water. So I use the relationship: Energy transferred = m1c1?T + m2c2?T Where c1 is the heating capacity of water (4.17Jg-1K-1) ...read more.

Conclusion

We can see that the error will be small in comparison to the whole value and so I do not feel that this error is significant enough to incorporate into my graph. Therefore the total error due to measurements was 3.09% which is not a significant amount to affect my results or my graph dramatically so I did not take into account theses errors in my calculations. But I could have reduced the error due to temperature change using the thermometer by using a data logger as it is more accurate and also gives almost instant temperature readings. There were also errors due to calculations of the change in enthalpy of combustion value. This error is shown below: The change in enthalpy of combustion of ethanol (CH3CH2OH) for my first experiment was -679KJmol-1 which is 600 plus or minus 10 because the value is in its hundreds. So the percentage error for each of these values is 1.7%, not a significant amount to change my graph by a large amount. Modifications of preliminary work justified: I used a cork lid on the can which greatly reduced the amount of energy loss through the top of the container and also kept in some evaporating vapour inside the container. This meant that my measurements of temperature could be more reliable. I used a tin foil draft excluder which reduced the draft from getting to the burner flame but I found that not enough oxygen was being supplied and so the flame went out a couple of times. To combat this problem I could have used an oxygen generator to supply to the flame. The tin foil resulted in my experiment to be less accurate because not enough oxygen was being supplied to the flame which in turn would have lead to a lower enthalpy change of combustion value. I used a tin can to insulate the copper container. This did not work and the heat energy from the flame was transferred to the water, then to the copper container and also then to the tin can. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level 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

# Related AS and A Level Organic Chemistry essays

1. ## Comparing the enthalpy changes of combustion of different alcohols

3 star(s)

lap coat and keep a distance between the flames Use the fire extinguisher and seek for help or call 911 Glassware Breaking/stabbing Do not touch Clean up with dustpan and brush = highly flammable. Ref: http://www.proshieldsafetysigns.co.uk/signs/4467_Hazchem_Signs_Labels_highly_flammable.html = irritant. Ref: http://nathalie1992.borsatoweblog.nl/log.php?id=85381 = toxic.

2. ## Experiment to measure the enthalpy change of combustion for hexane and methanol

equipment this would have affected the results of mass and temperature given lower values as not all the heat would have heated the water. 2. Also the heat may have not reached the calorimeter as the wind may have changed the direction of heat meaning that it couldn't have heated

1. ## Find the enthalpy change of combustion of a number of alcohol's' so that you ...

There are much more bonds to make and break in bigger alcohol's this therefore means that bigger alcohol's will have a high bond breaking enthalpy and therefore will have a very high bond making enthalpy. This in turn means that they will have a high enthalpy change of combustion.

2. ## The aim of this experiment is to produce Aspirin. This is an estrification in ...

16.10 cm3 16.15 cm3 16.05 cm3 Concordant results 16.10 cm3 16.15 cm3 Mass of aspirin used Accurate 1 = 0.3050g Accurate 2 = 0.3038g Accurate 3 = 0.3007g Pure aspirin Volume cm3 Accurate 1 Accurate 2 Accurate 3 Final 16.90 cm3 16.70 cm3 16.75 cm3 Start 0.00cm3 0.00cm3 0.00cm3 NaOH

1. ## Comparing the enthalpy changes of combustion of different alcohols

In other words, the enthalpy change of combustion of an alcohol increases as the length of the carbon chain is increased, due to an addition of a CH2 group. Risk Assessment As during this experiment I will be handling potentially harmful chemicals, several safety precautions must be made to ensure the safety of myself and others around me.

2. ## Investigating the Enthalpy Changes of Combustion of Alcohols.

the enthalpy is positive. The total energy needed to break the bonds is: (3 x 413) + 336 + 464 + (1.5 x 498.3) = +2786.45 kJmol-1 This is the amount of energy needed to atomise one mole of methanol.

1. ## The aim of this experiment is to investigate the enthalpy change of combustion for ...

Dipoles are caused by the difference in electronegativity between two atoms. Elecctronegativity is the ability of an atom to attract the bonding electrons from within a covalent bond towards itself. Oxygen is more electronegative than hydrogen and carbon and therefore attracts the electrons towards itself creating a partially negative charge

2. ## Experiment Hypothesis: The energy released by an alcohol increases as the number of carbon ...

The initial temperature of water was recorded (this has given the thermometer time to adjust) 4. The copper calorimeter was shielded to prevent heat loss to the environment and then clamped to a stand to keep it in the same position in the room and the same distance from the flame if possible.

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