Heat of Mixing: Ethanol and Water Abstract The temperature change when known amounts of water and ethanol were mixed was determined to see the enthalpy change in an isothermal and isobaric environment. Agreeable data was found compared to similar experiments. As the mole fraction increased of the solution so did the enthalpy until a certain limit of about 0. 32. Since water’s structure and unique properties affect many aspects of a solution, the solutions enthalpy’s decreased at a certain time due to ethanol’s non-electrolyte nature.

Introduction Johnson and Oatis (1) state that entropy is one of many reasons why a substance dissolves into another. Since nature tends to go towards a more random state, entropy is a significant factor. Other forces such as neutralization and changes in volume also play a role. As long as change in Gibbs free energy is negative a solution will be formed. An interest in the change of temperature of alcohol when dissolved in water is examined to determine the bonding interactions between ethanol and water. The interactions can either produce heat or absorb heat depending on many factors including a few mentioned before.

Theory Since an adiabatic system cannot be attained, heat calibrations are utilized by using known amounts of electrical energy into the solution and observing temperature rise. The electrical energy was found as follows assuming V is voltage and R is resistance: Qmix can then be put into a ratio form with equations 1 and 2 to produce: Another challenge arose since temperature change is affected by many factors which can leak heat in or out of the system. To overcome these challenges the temperature was taken over a period of 6 minutes total (2 before the mix, 2 during the mix, and 2 after the mix).

This is to obtain a linear plot with small changes to determine the ? T values. One last problem arose and that is temperature change must be measured very accurately. A thermistor was used to achieve this. A thermistor is a semi conductor device in which it is a sintered mix of metal oxides. At low temperatures the electrons in the semi metal band are bound tight together and do not conduct electricity. At higher temperatures the electrons can become excited by thermal energy and be promoted to the conduction band which they will conduct electricity.

Using a logarithmic derivation of Boltzmann’s equation and a calibration of the thermistor the following equation relates temperature to resistance: Experiment Discussion Conclusion The heat capacity and total enthalpy of the solution increased as the mole fraction of ethanol in a solution increased was seen. The heat capacity at approximately 0. 11 mole fraction of ethanol was seen to decrease where similarly at a mole fraction at about 0. 50 the solution’s enthalpy decreased. The nature of water tends to not let non electrolytes such as ethanol dissolve and allow an endothermic reaction.

There is a general agreement with Larkin with a few exceptions which have been noted and accounted for. References Larkin, J. A. , “thermodynamic properties of aqueous non-electrolyte mixture: I. Excess enthalpy for water+ethanol at 298. 15 to 383. 15 K”, J. Chem. Thermodynamics 7, 137-148 (1975). Johnson, P. ; Oatis, S. , “hot cocktails or cold? the heat of mixing of ethanol and water”, 1-10 (2009). Tables and Figures {draw:frame} Figure 1. Solution heated contained 3. 3398 g of ethanol and 51. 3473 g of water which, was then heated. {draw:frame} Figure 2. Solution heated contained 3. 398 g of ethanol and 51. 3473 g of water which, was then heated. {draw:frame} Figure 3. Solution heated contained 8. 09 g of ethanol and 51. 3473 g of water which, was then mixed. {draw:frame} Figure 4. Solution heated contained 8. 09 g of ethanol and 51. 3473 g of water which, was then heated. {draw:frame} Figure 5. Solution heated contained 15. 96 g of ethanol and 51. 3473 g of water which, was then mixed. {draw:frame} Figure 6. Solution heated contained 15. 96 g of ethanol and 51. 3473 g of water which, was then heated. {draw:frame} Figure 7. Solution heated contained 27. 80 g of ethanol and 51. 473 g of water which, was then mixed. {draw:frame} Figure 8. Solution heated contained 27. 80 g of ethanol and 51. 3473 g of water which, was then heated. {draw:frame} Figure 9. Solution heated contained 50. 0676 g of ethanol and 5. 02 g of water which, was then mixed. {draw:frame} Figure 10. Solution heated contained 50. 0676 g of ethanol and 5. 02 g of water which, was then heated. {draw:frame} Figure 11. Solution heated contained 50. 0676 g of ethanol and 12. 06 g of water which, was then mixed. {draw:frame} Figure 12. Solution heated contained 50. 0676 g of ethanol and 12. 6 g of water which, was then heated. {draw:frame} Figure 13. Solution heated contained 50. 0676 g of ethanol and 24. 07 g of water which, was then mixed. {draw:frame} Figure 14. Solution heated contained 50. 0676 g of ethanol and 24. 07 g of water which, was then heated. {draw:frame} Figure 15. Solution heated contained 50. 0676 g of ethanol and 42. 09 g of water which, was then mixed. {draw:frame} Figure 16. Solution heated contained 50. 0676 g of ethanol and 42. 09 g of water which, was then heated. {draw:frame} Figure 17. All eight heat of mixing trials. {draw:frame} Figure 18.

All eight electric heating trials. Table 1. Mass and moles of water and ethanol in the solutions. Table 2. Mole fractions of water and ethanol in the solutions. {draw:frame} Figure 19. When ethanol’s mole fraction reaches about 0. 10 the heat capacity decreases; any fraction less than 0. 10 the heat capacity increases. Table 3. Data for Figure 19. {draw:frame} Figure 20. The relationship of total enthalpy and ethanol’s mole fraction based on Larkin’s data. Table 4. Data for Figure 20. {draw:frame} Figure 21. The relationship between total enthalpy and the mole fraction of ethanol Table 5. Data for Figure 21.