Investigating the Link between Enthalpy of Combustion and Quantity of Carbons in Simple Alcohols of Identical Homologous Series

Alcohols have varied uses in today’s world, especially as fuels. Burning of alcohols produces water as well as energy which can be harnessed and used as biofuels. When used as biofuels, they are utilized in powering motor vehicles and in cooking (Wade 550-700). Ethanol is the most commonly used alcohol in the industrial level but recent studies have suggested that there are better options which are less corrosive and more efficient (Wade 550-700).. This mainly applies to branched alcohols but this paper will mainly look at straight chain alcohols for an easy and simplified analysis. This study would give an introductory phase for further studies. The paper delves into establishing a link between the energy output of various simple alcohols when they are subjected to heat and their structure. The study will precisely keep an eye on the numerical influence of carbon atoms forming the chain of homologous sequence of alcohols on the enthalpy variation of combustion.
Hypothesis
The initial phase of the hypothesis is that the enthalpy of combustion intensifies with the increase in the numerical quantities of carbon atoms. Variation in enthalpy comes about due to the variation in the energy levels needed for breaking the bonds in the alcohol chain and also from the energy released when forming new bonds. If the broken bonds are weaker than the newly-formed bonds, the released energy will be greater than the energy utilized (Wade 550-700).; as a result, this resultant energy will be released to the surroundings.

This is the energy that can be harnessed and used as biofuels.
Combustion of alcohols in the presence of oxygen results in the formation of carbon dioxide and water. When alcohols react with oxygen in the air, they form carbon dioxide and water. The newly-formed bond between oxygen and carbon has a double bond and hence stronger than single bonds between carbons and hence energy is released. As a result, double bonds will be formed for every carbon atom and hence the enthalpy should directly intensify as the number of carbon atoms increase.
The second part of this investigation is also geared towards the aspect of bonds and deals with the alterations prevailing between enthalpy variations experimentally obtained compared to those worked out by use of bond energies. The worked out values are the averages of a number of compounds with the same structure. As for alcohols like methanol, the energy levels required to break the bond between a Carbon and Oxygen atom (C) when the carbon atom is bonded to Hydrogen atoms should be dissimilar to other carbons. According to my hypothesis, the value for methanol will be a bit lower since methyl group has a greater inductive influence in comparison to other alkyl groups. Moreover, the variation between other alcohols will be lesser since the carbon atom bonded to Oxygen atom has another carbon atom bonded to it and hence more electronegativity; this means no inductive effect and only the hydrogen atoms will be the ones providing the effect.
Results and Analysis
So at to prove the hypothesis, values from the (“RSC: Advancing The Chemical Sciences: Hydration Enthalpies Of Selected Ions”) Royal Society of Chemistry was my database of choice as an alternative of doing the actual experiment. The data obtained from the database for various alcohols was represented in a tabular form as shown below in Table The various balanced chemical reactions that occur are shown below:
016344Table 1: Table showing enthalpy changes of combustion based on Bond energies
Table 1: Table showing enthalpy changes of combustion based on Bond energies

The comparison between the theoretical values and those obtained from calculation using bond energies gives a clear picture of the experiment. The illustrated bond energies are the average values got from numerous related compounds. The main dissimilarity between them and hypothetical experimental is that they do not precisely take into consideration the changes coming from variations in the chemical environment near the specific bonds. The table below shows the comparison.

Graphically, the enthalpy of combustion released per moles in terms of carbon atoms in the structure can be represented as shown below. The graphs compare the theoretical value and the calculated value.

Discussion
From the results, it can be seen that both the calculated vale and the theoretical value have a positive relative which authenticates my hypothesis. The calculated values are a bit lesser than the experimental ones. The database used gives the HO value conforming to water which ought to be dissimilar from that in hydroxyls as the chemicals extensively differ. It is worth noting that the ethanol’s experimental value seems to be lower than that of other alcohols. However, this is not seen in the values calculated from band energy where all the energy values are seamlessly aligned.
The value of ethanol is evidently inferior as compared to methanol and somewhat lower in comparison to other higher alcohols. Consequently, it seems there are some structural variations between other alcohols and ethanol. The first member of the homologous series is different from the rest. My belief is that this is due to the significantly inferior inductive influence that the ethyl group member has the CO bond in comparison to the methyl group. The lower the effect of induction, the bond becomes less polar and hence there is an increased covalence which leads to a stronger bond.
When the bond gets stronger, it means that more energy is required to break it and hence the enthalpy of combustion change would be lesser. The effect of induction is not affected by adding a CH2 in higher alcohols but there is still some induction effect. The inductive effect in higher alcohols is lower than that of methanol. The inductive effect is not changed by adding CH2 in the higher alcohols since they are perfectly aligned to each other (Wade 550-700). The other possibility that can bring about differences is experimental errors which are inevitable.
The obtained outcomes may indicate that the variation in the bond OH maybe influencing the alcohols to a certain degree. More research is needed to investigate why the second CH2 influences the CO bond in ethanol and in the rest. The established values of bond energies agree to both reactants and products in gaseous states although the experimental values handle the liquid states for water and alcohols.
Conclusion
In a nutshell, my hypothesis has been authenticated by both the calculated value and the experimental values in cited sources. The study has shown that there is a positive linear relationship between the enthalpy of combustion and the number of carbon atoms in a homologous sequence of normal alcohols. Moreover, the study has indicated that the calculated values based on bond energies are slightly inferior to the ones obtained experimentally and this underlines the need to put into account the chemical surroundings.
Works Cited
“Datasheets Hydration Enthalpies of Selected Ions.” RSC: Advancing the Chemical Sciences : Hydration Enthalpies of Selected Ions. N.p., n.d. Web. 10 Nov. 2016.
Wade, L. G. Organic Chemistry. Upper Saddle River, NJ: Pearson Prentice Hall, 2006. Print.