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# To calculate the energy per mole of substance

Extracts from this document...

Introduction

The Tables To calculate the energy per mole of substance, simply divide the number of moles which you calculated were burned into 1. because you only burned a fraction of a mole of each alcohol in each test, the answer you get when you divide 1 by the number of moles tells you how many times you must multiply the energy result in you table by, to get the energy per 1mole of substance. For this reason you should use s formulae of this form: 1 . number of moles of substance burned * energy value in table = energy per mole of substance. So energy per mole = energy value from table(1/number of moles burned) The structural formula: The letter corresponds to the element it represents from the periodic table. The single line which links it to another letter signifies a single bond between it and the other element. The structural formula: C3H7OH The letter represents it's corresponding element from the periodic table, the subscripted number on the lower right side of the letter signifies how many of those similar elements there are in the compound. ...read more.

Middle

1 2 3 mean average total mass of burner before burning (g) 102.45 102.55 106.35 103.78 total mass of burner after burning (g) 102.20 102.30 106.10 103.53 mass of alcohol burned (g) 0.25 0.25 0.25 0.25 mass of water (kg) 0.1400 0.1405 0.1395 0.1400 starting temperature (deg. Centigrade) 17.00 17.00 17.00 17.00 final temperature (deg. Centigrade) 28.00 28.00 28.00 28.00 change in temperature (deg. Centigrade) 11.00 11.00 11.00 11.00 RMM 60.00 60.00 60.00 60.00 moles of substance burned =Mass/RMM 0.0042 0.0042 0.0042 0.0042 energy=mc 6.47 6.49 6.44 6.47 energy per mole = energy value from table(1/number of moles burned) =6.47(1/0.0042) =1540.4762kj/mole so an alcohol with a chain length three carbons long will release 1540.4762kj/mole when burnt. Structural formula: Molecular formula: C3H7OH Total number of bonds between elements:10 Combustion of propanol: C3H7OH + 4.5O2 --> 4H2O + 3CO2 Butanol (C4H9OH) 1 2 3 mean average total mass of burner before burning (g) 83.90 89.40 77.40 83.57 total mass of burner after burning (g) 83.60 89.10 77.10 83.27 mass of alcohol burned (g) 0.30 0.30 0.30 0.30 mass of water (kg) ...read more.

Conclusion

From this table it is possible to conclude that as the number of carbons in the alcohol increases, so does the energy of the reaction. This is because during any reaction bonds are broken, so all the atoms are left unattached to each other, then in the end of the reaction the atoms re-attach, forming a different compound than that which was present in the beginning. In any reaction, energy is required to break bonds, and energy is released bonds are made. The amount of energy required or released depends upon the types of bonds being made or broken. In an exothermic reaction, there is more energy released from the formation of the bonds than was required to break the bonds. This extra energy is released as thermal (heat) energy. In an endothermic reaction, heat is "Taken in" from the surroundings, because less energy is released when the bonds were made than was required to break the bonds, the extra energy required is taken from the environment around the reactants. The amount of energy required may be displayed in a chart called a reaction profile. This tracks the energy change through the course of the reaction. The energy profiles for the five alcohols are displayed: Methanol: Ethanol: Propanol: Butanol: Pentanol: Reaction profiles: ...read more.

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